Risk of developing gallbladder cancer in patients with gallbladder polyps detected on transabdominal ultrasound: a systematic review and meta-analysis

OBJECTIVE

To estimate the risk of malignancy in gallbladder polyps of incremental sizes detected during transabdominal ultrasound (TAUS).

METHODS

We searched databases including MEDLINE, Embase, and Cochrane Library for eligible studies recording the polyp size from which gallbladder malignancy developed, confirmed following cholecystectomy, or by subsequent follow-up. Primary outcome was the risk of gallbladder cancer in patients with polyps. Secondary outcome was the effect of polyp size as a prognostic factor for cancer. Risk of bias was assessed using the Quality in Prognostic Factor Studies (QUIPS) tool. Bayesian meta-analysis estimated the median cancer risk according to polyp size. This study is registered with PROSPERO (CRD42020223629).

RESULTS

82 studies published since 1990 reported primary data for 67,837 patients. 67,774 gallbladder polyps and 889 cancers were reported. The cumulative median cancer risk of a polyp measuring 10 mm or less was 0.60% (99% credible range 0.30-1.16%). Substantial heterogeneity existed between studies (I2 = 99.95%, 95% credible interval 99.86-99.98%). Risk of bias was generally high and overall confidence in evidence was low. 13 studies (15.6%) were graded with very low certainty, 56 studies (68.3%) with low certainty, and 13 studies (15.6%) with moderate certainty. In studies considered moderate quality, TAUS monitoring detected 4.6 cancers per 10,000 patients with polyps less than 10 mm.

CONCLUSION

Malignant risk in gallbladder polyps is low, particularly in polyps less than 10 mm, however the data are heterogenous and generally low quality. International guidelines, which have not previously modelled size data, should be informed by these findings.

ADVANCES IN KNOWLEDGE

This large systematic review and meta-analysis has shown that the mean cumulative risk of small gallbladder polyps is low, but heterogeneity and missing data in larger polyp sizes (>10 mm) means the risk is uncertain and may be higher than estimated.Studies considered to have better methodological quality suggest that previous estimates of risk are likely to be inflated.

Measuring and exploring mental health determinants: a closer look at co-residents’ effect using a multilevel structural equations model

Objective

Previous research has demonstrated that individual risk of mental illness is associated with individual, co-resident, and household risk factors. However, modelling the overall effect of these risk factors presents several methodological challenges. In this study we apply a multilevel structural equation model (MSEM) to address some of these challenges and the impact of the different determinants when measuring mental health risk.

Study design and setting

Two thousand, one hundred forty-three individuals aged 16 and over from 888 households were analysed based on the Household Survey for England-2014 dataset. We applied MSEM to simultaneously measure and identify psychiatric morbidity determinants while accounting for the dependency among individuals within the same household and the measurement errors.

Results

Younger age, female gender, non-working status, headship of the household, having no close relationship with other people, having history of mental illness and obesity were all significant (p < 0.01) individual risk factors for psychiatric morbidity. A previous history of mental illness in the co-residents, living in a deprived household, and a lack of closeness in relationships among residents were also significant predictors. Model fit indices showed a very good model specification (CFI = 0.987, TLI = 0.980, RMSEA = 0.023, GFI = 0.992).

Conclusion

Measuring and addressing mental health determinants should consider not only an individual’s characteristics but also the co-residents and the households in which they live.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12874-022-01711-9.

Comparing outcomes from tailored meta-analysis with outcomes from a setting specific test accuracy study using routine data of faecal calprotectin testing for inflammatory bowel disease

Background

Meta-analyses of test accuracy studies may provide estimates that are highly improbable in clinical practice. Tailored meta-analysis produces plausible estimates for the accuracy of a test within a specific setting by tailoring the selection of included studies compatible with a specific setting using information from the target setting. The aim of this study was to validate the tailored meta-analysis approach by comparing outcomes from tailored meta-analysis with outcomes from a setting specific test accuracy study.

Methods

A retrospective cohort study of primary care electronic health records provided setting-specific data on the test positive rate and disease prevalence. This was used to tailor the study selection from a review of faecal calprotectin testing for inflammatory bowel disease for meta-analysis using the binomial method and the Mahalanobis distance method. Tailored estimates were compared to estimates from a study of test accuracy in primary care using the same routine dataset.

Results

Tailoring resulted in the inclusion of 3/14 (binomial method) and 9/14 (Mahalanobis distance method) studies in meta-analysis. Sensitivity and specificity from tailored meta-analysis using the binomial method were 0.87 (95% CI 0.77 to 0.94) and 0.65 (95% CI 0.60 to 0.69) and 0.98 (95% CI 0.83 to 0.999) and 0.68 (95% CI 0.65 to 0.71), respectively using the Mahalanobis distance method. The corresponding estimates for the conventional meta-analysis were 0.94 (95% CI 0.90 to 0.97) and 0.67 (95% CI 0.57 to 0.76) and for the FC test accuracy study of primary care data 0.93 (95%CI 0.89 to 0.96) and 0.61 (95% CI 0.6 to 0.63) to detect IBD at a threshold of 50 μg/g. Although the binomial method produced a plausible estimate, the tailored estimates of sensitivity and specificity were not closer to the primary study estimates than the estimates from conventional meta-analysis including all 14 studies.

Conclusions

Tailored meta-analysis does not always produce estimates of sensitivity and specificity that lie closer to the estimates derived from a primary study in the setting in question. Potentially, tailored meta-analysis may be improved using a constrained model approach and this requires further investigation.

Long-term impact of pre-incision antibiotics on children born by caesarean section: a longitudinal study based on UK electronic health records

BACKGROUND

Since changes in the national guidance in 2011, prophylactic antibiotics for women undergoing caesarean section are recommended prior to skin incision, rather than after the baby's umbilical cord has been clamped. Evidence from randomised controlled trials conducted outside the UK has shown that this reduces maternal infectious morbidity; however, the prophylactic antibiotics also cross the placenta, meaning that babies are exposed to them around the time of birth. Antibiotics are known to affect the gut microbiota of the babies, but the long-term effects of exposure to high-dose broad-spectrum antibiotics around the time of birth on allergy and immune-related diseases are unknown.

OBJECTIVES

We aimed to examine whether or not in-utero exposure to antibiotics immediately prior to birth compared with no pre-incisional antibiotic exposure increases the risk of (1) asthma and (2) eczema in children born by caesarean section.

DESIGN

This was a controlled interrupted time series study.

SETTING

The study took place in primary and secondary care.

PARTICIPANTS

Children born in the UK during 2006-18 delivered by caesarean section were compared with a control cohort delivered vaginally.

INTERVENTIONS

In-utero exposure to antibiotics immediately prior to birth.

MAIN OUTCOME MEASURES

Asthma and eczema in children in the first 5 years of life. Additional secondary outcomes, including other allergy-related conditions, autoimmune diseases, infections, other immune system-related diseases and neurodevelopmental conditions, were also assessed.

DATA SOURCES

The Health Improvement Network (THIN) and the Clinical Practice Research Datalink (CPRD) primary care databases and the Hospital Episode Statistics (HES) database. Previously published linkage strategies were adapted to link anonymised data on mothers and babies in these databases. Duplicate practices contributing to both THIN and the CPRD databases were removed to create a THIN-CPRD data set.

RESULTS

In the THIN-CPRD and HES data sets, records of 515,945 and 3,945,351 mother-baby pairs were analysed, respectively. The risk of asthma was not significantly higher in children born by caesarean section exposed to pre-incision antibiotics than in children whose mothers received post-cord clamping antibiotics, with an incidence rate ratio of 0.91 (95% confidence interval 0.78 to 1.05) for diagnosis of asthma in primary care and an incidence rate ratio of 1.05 (95% confidence interval 0.99 to 1.11) for asthma resulting in a hospital admission. We also did not find an increased risk of eczema, with an incidence rate ratio of 0.98 (95% confidence interval 0.94 to1.03) and an incidence rate ratio of 0.96 (95% confidence interval 0.71 to 1.29) for diagnosis in primary care and hospital admissions, respectively.

LIMITATIONS

It was not possible to ascertain the exposure to pre-incision antibiotics at an individual level. The maximum follow-up of children was 5 years.

CONCLUSIONS

There was no evidence that the policy change from post-cord clamping to pre-incision prophylactic antibiotics for caesarean sections during 2006-18 had an impact on the incidence of asthma and eczema in early childhood in the UK.

FUTURE WORK

There is a need for further research to investigate if pre-incision antibiotics have any impact on developing asthma and other allergy and immune-related conditions in older children.

STUDY REGISTRATION

This study is registered as researchregistry3736.

FUNDING

This project was funded by the National Institute for Health and Care Research (NIHR) Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 26, No. 30. See the NIHR Journals Library website for further project information.

Long term impact of prophylactic antibiotic use before incision versus after cord clamping on children born by caesarean section: longitudinal study of UK electronic health records

OBJECTIVE

To investigate the impact on child health up to age 5 years of a policy to use antibiotic prophylaxis for caesarean section before incision compared with after cord clamping.

DESIGN

Observational controlled interrupted time series study.

SETTING

UK primary and secondary care.

PARTICIPANTS

515 945 children born in 2006-18 with linked maternal records and registered with general practices contributing to two UK primary care databases (The Health Improvement Network and Clinical Practice Research Datalink), and 7 147 884 children with linked maternal records in the Hospital Episode Statistics database covering England, of which 3 945 351 were linked to hospitals that reported the year of policy change to administer prophylactic antibiotics for caesarean section before incision rather than after cord clamping.

INTERVENTION

Fetal exposure to antibiotics shortly before birth (using pre-incision antibiotic policy as proxy) compared with no exposure.

MAIN OUTCOME MEASURES

The primary outcomes were incidence rate ratios of asthma and eczema in children born by caesarean section when pre-incision prophylactic antibiotics were recommended compared with those born when antibiotics were administered post-cord clamping, adjusted for temporal changes in the incidence rates in children born vaginally.

RESULTS

Prophylactic antibiotics administered before incision for caesarean section compared with after cord clamping were not associated with a significantly higher risk of asthma (incidence rate ratio 0.91, 95% confidence interval 0.78 to 1.05) or eczema (0.98, 0.94 to 1.03), including asthma and eczema resulting in hospital admission (1.05, 0.99 to 1.11 and 0.96, 0.71 to 1.29, respectively), up to age 5 years.

CONCLUSIONS

This study found no evidence of an association between pre-incision prophylactic antibiotic use and risk of asthma and eczema in early childhood in children born by caesarean section.

Clustering functional data using forward search based on functional spatial ranks with medical applications

Cluster analysis of functional data is finding increasing application in the field of medical research and statistics. Here we introduce a functional version of the forward search methodology for the purpose of functional data clustering. The proposed forward search algorithm is based on the functional spatial ranks and is a data-driven non-parametric method. It does not require any preprocessing functional data steps, nor does it require any dimension reduction before clustering. The Forward Search Based on Functional Spatial Rank (FSFSR) algorithm identifies the number of clusters in the curves and provides the basis for the accurate assignment of each curve to its cluster. We apply it to three simulated datasets and two real medical datasets, and compare it with six other standard methods. Based on both simulated and real data, the FSFSR algorithm identifies the correct number of clusters. Furthermore, when compared with six standard methods used for clustering and classification, it records the lowest misclassification rate. We conclude that the FSFSR algorithm has the potential to cluster and classify functional data.

The incidence and prevalence of inflammatory bowel disease in UK primary care: a retrospective cohort study of the IQVIA Medical Research Database

BACKGROUND

Our knowledge of the incidence and prevalence of inflammatory bowel disease (IBD) is uncertain. Recent studies reported an increase in prevalence. However, they excluded a high proportion of ambiguous cases from general practice. Estimates are needed to inform health care providers who plan the provision of services for IBD patients. We aimed to estimate the IBD incidence and prevalence in UK general practice.

METHODS

We undertook a retrospective cohort study of routine electronic health records from the IQVIA Medical Research Database covering 14 million patients. Adult patients from 2006 to 2016 were included. IBD was defined as an IBD related Read code or record of IBD specific medication. Annual incidence and 12-month period prevalence were calculated.

RESULTS

The prevalence of IBD increased between 2006 and 2016 from 106.2 (95% CI 105.2-107.3) to 142.1 (95% CI 140.7-143.5) IBD cases per 10,000 patients which is a 33.8% increase. Incidence varied across the years. The incidence across the full study period was 69.5 (95% CI 68.6-70.4) per 100,000 person years.

CONCLUSIONS

In this large study we found higher estimates of IBD incidence and prevalence than previously reported. Estimates are highly dependent on definitions of disease and previously may have been underestimated.

Preferred reporting items for journal and conference abstracts of systematic reviews and meta-analyses of diagnostic test accuracy studies (PRISMA-DTA for Abstracts): checklist, explanation, and elaboration

For many users of the biomedical literature, abstracts may be the only source of information about a study. Hence, abstracts should allow readers to evaluate the objectives, key design features, and main results of the study. Several evaluations have shown deficiencies in the reporting of journal and conference abstracts across study designs and research fields, including systematic reviews of diagnostic test accuracy studies. Incomplete reporting compromises the value of research to key stakeholders. The authors of this article have developed a 12 item checklist of preferred reporting items for journal and conference abstracts of systematic reviews and meta-analyses of diagnostic test accuracy studies (PRISMA-DTA for Abstracts). This article presents the checklist, examples of complete reporting, and explanations for each item of PRISMA-DTA for Abstracts.

Test accuracy of faecal calprotectin for inflammatory bowel disease in UK primary care: a retrospective cohort study of the IMRD-UK data

OBJECTIVE

To estimate the test accuracy of faecal calprotectin (FC) for inflammatory bowel disease (IBD) in the primary care setting using routine electronic health records.

DESIGN

Retrospective cohort test accuracy study.

SETTING

UK primary care.

PARTICIPANTS

5970 patients (≥18 years) without a previous IBD diagnosis and with a first FC test between 1 January 2006 and 31 December 2016. We excluded multiple tests and tests without numeric results in units of µg/g.

INTERVENTION

FC testing for the diagnosis of IBD. Disease status was confirmed by a recorded diagnostic code and/or a drug code of an IBD-specific medication at three time points after the FC test date.

MAIN OUTCOME MEASURES

Sensitivity, specificity, and positive and negative predictive values for the differential of IBD versus non-IBD and IBD versus irritable bowel syndrome (IBS) at the 50 and 100 µg/g thresholds.

RESULTS

5970 patients met the inclusion criteria and had at least 6 months of follow-up data after FC testing. 1897 had an IBS diagnosis, 208 had an IBD diagnosis, 31 had a colorectal cancer diagnosis, 80 had more than one diagnosis and 3754 had no subsequent diagnosis. Sensitivity, specificity, and positive and negative predictive values were 92.9% (88.6% to 95.6%), 61.5% (60.2% to 62.7%), 8.1% (7.1% to 9.2%) and 99.6% (99.3% to 99.7%), respectively, at the threshold of 50 µg/g. Raising the threshold to 100 µg/g missed less than 7% additional IBD cases. Longer follow-up had no effect on test accuracy. Overall, uncertainty was greater for specificity than sensitivity. General practitioners' (GPs') referral decisions did not follow the anticipated clinical pathways in national guidance.

CONCLUSIONS

GPs can be confident in excluding IBD on the basis of a negative FC test in a population with low pretest risk but should interpret a positive test with caution. The applicability of national guidance to general practice needs to be improved.

Long-term impact of giving antibiotics before skin incision versus after cord clamping on children born by caesarean section: protocol for a longitudinal study based on UK electronic health records

INTRODUCTION

In the UK, about a quarter of women give birth by caesarean section (CS) and are offered prophylactic broad-spectrum antibiotics to reduce the risk of maternal postpartum infection. In 2011, national guidance was changed from recommending antibiotics after the umbilical cord was cut to giving antibiotics prior to skin incision based on evidence that earlier administration reduces maternal infectious morbidity. Although antibiotics cross the placenta, there are no known short-term harms to the baby. This study aims to address the research gap on longer term impact of these antibiotics on child health.

METHODS AND ANALYSIS

A controlled interrupted time series study will use anonymised mother-baby linked routine electronic health records for children born during 2006-2018 recorded in UK primary care (The Health Improvement Network, THIN and Clinical Practice Research Datalink, CPRD) and secondary care (Hospital Episode Statistics, HES) databases. The primary outcomes of interest are asthma and eczema, two common allergy-related diseases in childhood. In-utero exposure to antibiotics immediately prior to CS will be compared with no exposure when given after cord clamping. The risk of outcomes in children delivered by CS will also be compared with a control cohort delivered vaginally to account for time effects. We will use all available data from THIN, CPRD and HES with estimated power of 80% and 90% to detect relative increase in risk of asthma of 16% and 18%, respectively at the 5% significance level.

ETHICS AND DISSEMINATION

Ethical approval has been obtained from the University of Birmingham Ethical Review Committee with scientific approvals obtained from the independent scientific advisory committees from the Medicines and Healthcare products Regulatory Agency for CPRD and the data provider, IQVIA for THIN. The results will be published in peer-reviewed journals, presented at national and international conferences and disseminated to stakeholders.

Maximum likelihood estimation based on Newton-Raphson iteration for the bivariate random effects model in test accuracy meta-analysis

A bivariate generalised linear mixed model is often used for meta-analysis of test accuracy studies. The model is complex and requires five parameters to be estimated. As there is no closed form for the likelihood function for the model, maximum likelihood estimates for the parameters have to be obtained numerically. Although generic functions have emerged which may estimate the parameters in these models, they remain opaque to many. From first principles we demonstrate how the maximum likelihood estimates for the parameters may be obtained using two methods based on Newton-Raphson iteration. The first uses the profile likelihood and the second uses the Observed Fisher Information. As convergence may depend on the proximity of the initial estimates to the global maximum, each algorithm includes a method for obtaining robust initial estimates. A simulation study was used to evaluate the algorithms and compare their performance with the generic generalised linear mixed model function glmer from the lme4 package in R before applying them to two meta-analyses from the literature. In general, the two algorithms had higher convergence rates and coverage probabilities than glmer. Based on its performance characteristics the method of profiling is recommended for fitting the bivariate generalised linear mixed model for meta-analysis.

Faecal calprotectin to detect inflammatory bowel disease: a systematic review and exploratory meta-analysis of test accuracy

OBJECTIVE

Test accuracy of faecal calprotectin (FC) testing in primary care is inconclusive. We aimed to assess the test accuracy of FC testing in primary care and compare it to secondary care estimates for the detection of inflammatory bowel disease (IBD).

METHODS

Systematic review and meta-analysis of test accuracy using a bivariate random effects model. We searched MEDLINE, EMBASE, Cochrane Library and Web of Science until 31 May 2017 and included studies from auto alerts up until 31 January 2018. Eligible studies measured FC levels in stool samples to detect IBD in adult patients with chronic (at least 6-8 weeks) abdominal symptoms in primary or secondary care. Risk of bias and applicability were assessed using the Quality Assessment of Diagnostic Accuracy Studies-2 criteria. We followed the protocol registered as PROSPERO CRD 42012003287.

RESULTS

38 out of 2168 studies were eligible including five from primary care. Comparison of test accuracy by setting was precluded by extensive heterogeneity. Overall, summary estimates of sensitivity and specificity were not recorded. At a threshold of 50 µg/g, sensitivity from separate meta-analysis of four assay types ranged from 0.85 (95% CI 0.75 to 0.92) to 0.94 (95% CI 0.75 to 0.90) and specificity from 0.67 (95% CI 0.56 to 0.76) to 0.88 (95% CI 0.77 to 0.94). Across three different definitions of disease, sensitivity ranged from 0.80 (95% CI 0.76 to 0.84) to 0.97 (95% CI 0.91 to 0.99) and specificity from 0.67 (95% CI 0.58 to 0.75) to 0.76 (95% CI 0.66 to 0.84). Sensitivity appears to be lower in primary care and is further reduced at a revised threshold of 100 µg/g.

CONCLUSIONS

Conclusive estimates of sensitivity and specificity of FC testing in primary care for the detection of IBD are still missing. There is insufficient evidence in the published literature to support the decision to introduce FC testing in primary care. Studies evaluating FC testing in an appropriate primary care setting are needed.

Visual and radiographic caries detection: a tailored meta-analysis for two different settings, Egypt and Germany

Background

Diagnostic meta-analyses on caries detection methods should assist practitioners in their daily practice. However, conventional meta-analysis estimates may be inapplicable due to differences in test conduct, applied thresholds and assessed population between settings. Our aim was to demonstrate the impact of tailored meta-analysis of visual and radiographic caries detection to different settings using setting-specific routine data.

Methods

Published systematic reviews and meta-analyses on the accuracy of visual and radiographic caries detection were used. In two settings (a private practice in Germany and a public health clinic in Egypt), routine data of a total of 100 (n = 50/practice) consecutive 12–14 year-olds were collected. Test-positive rates of visual and radiographic detection for initial and advanced carious lesions on occlusal or proximal surfaces of molars were used to tailor meta-analyses. If prevalence data were available, these were also used for tailoring.

Results

From the original reviews, 210 and 100 heterogeneous studies on visual and radiographic caries detection were included in our meta-analyses. For radiographic detection, sensitivity and specificity estimates derived from conventional and tailored meta-analysis were similar. For visual detection of advanced occlusal carious lesions, the conventional meta-analysis yielded a sensitivity and specificity (95% CI) of 64.6% (57–71) and 90.9% (88–93), whereas the tailored estimates for Egypt were 75.1% (70–81) and 84.9% (82–89), respectively, and 43.7% (37–51) and 96.5% (95–97) for Germany, respectively.

Conclusion

Conventional test accuracy meta-analyses may yield aggregate estimates which are inapplicable to specific settings. Routine data may be used to produce a meta-analysis estimate which is tailored to the setting and thereby improving its applicability.

Electronic supplementary material

The online version of this article (10.1186/s12903-018-0561-z) contains supplementary material, which is available to authorized users.

Preferred Reporting Items for a Systematic Review and Meta-analysis of Diagnostic Test Accuracy Studies: The PRISMA-DTA Statement

Importance

Systematic reviews of diagnostic test accuracy synthesize data from primary diagnostic studies that have evaluated the accuracy of 1 or more index tests against a reference standard, provide estimates of test performance, allow comparisons of the accuracy of different tests, and facilitate the identification of sources of variability in test accuracy.

Objective

To develop the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) diagnostic test accuracy guideline as a stand-alone extension of the PRISMA statement. Modifications to the PRISMA statement reflect the specific requirements for reporting of systematic reviews and meta-analyses of diagnostic test accuracy studies and the abstracts for these reviews.

Design

Established standards from the Enhancing the Quality and Transparency of Health Research (EQUATOR) Network were followed for the development of the guideline. The original PRISMA statement was used as a framework on which to modify and add items. A group of 24 multidisciplinary experts used a systematic review of articles on existing reporting guidelines and methods, a 3-round Delphi process, a consensus meeting, pilot testing, and iterative refinement to develop the PRISMA diagnostic test accuracy guideline. The final version of the PRISMA diagnostic test accuracy guideline checklist was approved by the group.

Findings

The systematic review (produced 64 items) and the Delphi process (provided feedback on 7 proposed items; 1 item was later split into 2 items) identified 71 potentially relevant items for consideration. The Delphi process reduced these to 60 items that were discussed at the consensus meeting. Following the meeting, pilot testing and iterative feedback were used to generate the 27-item PRISMA diagnostic test accuracy checklist. To reflect specific or optimal contemporary systematic review methods for diagnostic test accuracy, 8 of the 27 original PRISMA items were left unchanged, 17 were modified, 2 were added, and 2 were omitted.

Conclusions and Relevance

The 27-item PRISMA diagnostic test accuracy checklist provides specific guidance for reporting of systematic reviews. The PRISMA diagnostic test accuracy guideline can facilitate the transparent reporting of reviews, and may assist in the evaluation of validity and applicability, enhance replicability of reviews, and make the results from systematic reviews of diagnostic test accuracy studies more useful.

Measuring the statistical validity of summary meta-analysis and meta-regression results for use in clinical practice

An important question for clinicians appraising a meta‐analysis is: are the findings likely to be valid in their own practice—does the reported effect accurately represent the effect that would occur in their own clinical population? To this end we advance the concept of statistical validity—where the parameter being estimated equals the corresponding parameter for a new independent study. Using a simple (‘leave‐one‐out’) cross‐validation technique, we demonstrate how we may test meta‐analysis estimates for statistical validity using a new validation statistic, Vn, and derive its distribution.

We compare this with the usual approach of investigating heterogeneity in meta‐analyses and demonstrate the link between statistical validity and homogeneity. Using a simulation study, the properties of Vn and the Q statistic are compared for univariate random effects meta‐analysis and a tailored meta‐regression model, where information from the setting (included as model covariates) is used to calibrate the summary estimate to the setting of application. Their properties are found to be similar when there are 50 studies or more, but for fewer studies Vn has greater power but a higher type 1 error rate than Q. The power and type 1 error rate of Vn are also shown to depend on the within‐study variance, between‐study variance, study sample size, and the number of studies in the meta‐analysis. Finally, we apply Vn to two published meta‐analyses and conclude that it usefully augments standard methods when deciding upon the likely validity of summary meta‐analysis estimates in clinical practice. © 2017 The Authors. Statistics in Medicine published by John Wiley & Sons Ltd.

All-Cause Mortality in Patients With Diabetes Under Treatment With Dapagliflozin: A Population-Based, Open-Cohort Study in The Health Improvement Network Database

CONTEXT

Empagliflozin was found to decrease mortality in patients with type 2 diabetes mellitus (T2DM) and a prior cardiovascular disease (CVD) event.

OBJECTIVES

To establish whether these benefits can be replicated in a real-world setting, should be expected with the use of dapagliflozin, and apply to T2DM patients at low risk of CVD.

DESIGN

General practice, population-based, retrospective cohort study (January 2013 to September 2015).

SETTING

The Health Improvement Network database.

PARTICIPANTS

A total of 22,124 T2DM patients (4444 exposed to dapagliflozin; 17,680 unexposed T2DM patients) matched for age, sex, body mass index, T2DM duration, and smoking.

MAIN OUTCOME MEASURES

The primary outcome was all-cause mortality (high and low risk for CVD) in the total study population, expressed as the adjusted incidence rate ratio (aIRR) with 95% confidence intervals (CIs). As a secondary analysis in the low-risk population, all-cause mortality and incident CVD were considered.

RESULTS

Patients with T2DM exposed to dapagliflozin were significantly less likely to die of any cause (aIRR: 0.50; 95% CI: 0.33 to 0.75; P = 0.001). Similarly, in low-risk patients, death from any cause was significantly lower in the cohort exposed to dapagliflozin (aIRR: 0.44; 95% CI: 0.25 to 0.78; P = 0.002). The difference in the risk of incident CVD did not reach statistical significance between groups in low-risk patients (aIRR: 0.89; 95% CI: 0.61 to 1.31; P = 0.546).

CONCLUSIONS

Patients with T2DM who were exposed to dapagliflozin had a lower risk of death from any cause irrespective of baseline CVD status.

Type 1 diabetes mellitus and risk of incident epilepsy: a population-based, open-cohort study

AIMS/HYPOTHESIS

The aim of this research was to explore the relationship between incident epilepsy and type 1 diabetes in British participants.

METHODS

Using The Health Improvement Network database, we conducted a retrospective, open-cohort study. Patients who were newly diagnosed with type 1 diabetes mellitus at the age of ≤40 years were identified and followed-up from 1 January 1990 to 15 September 2015. These patients, identified as not suffering from epilepsy at the time of diagnosis, were randomly matched with up to four individuals without type 1 diabetes mellitus, based on age, sex and participating general practice. A Cox regression analysis was subsequently performed using Townsend deprivation index, cerebral palsy, head injury and learning disabilities as model covariates.

RESULTS

The study population consisted of a total of 24,610 individuals (4922 with type 1 diabetes and 19,688 controls). These individuals were followed up for a mean of 5.4 years (approximately 132,000 person-years of follow up). Patients with type 1 diabetes were significantly more likely to be diagnosed with epilepsy during the observation period compared with controls (crude HR [95% CI]: 3.02 [1.95, 4.69]). The incidence rate was estimated to be 132 and 44 per 100,000 person-years in patients and controls, respectively. This finding persisted after adjusting for model covariates (adjusted HR [95% CI]: 3.01 [1.93, 4.68]) and was also robust to sensitivity analysis, excluding adult-onset type 1 diabetes mellitus.

CONCLUSIONS/INTERPRETATION

Patients with type 1 diabetes are at approximately three-times greater risk of developing epilepsy compared with matched controls without type 1 diabetes. This should be considered when investigating seizure-related disorders in patients with type 1 diabetes mellitus.

Summarising and validating test accuracy results across multiple studies for use in clinical practice

Following a meta-analysis of test accuracy studies, the translation of summary results into clinical practice is potentially problematic. The sensitivity, specificity and positive (PPV) and negative (NPV) predictive values of a test may differ substantially from the average meta-analysis findings, because of heterogeneity. Clinicians thus need more guidance: given the meta-analysis, is a test likely to be useful in new populations, and if so, how should test results inform the probability of existing disease (for a diagnostic test) or future adverse outcome (for a prognostic test)? We propose ways to address this. Firstly, following a meta-analysis, we suggest deriving prediction intervals and probability statements about the potential accuracy of a test in a new population. Secondly, we suggest strategies on how clinicians should derive post-test probabilities (PPV and NPV) in a new population based on existing meta-analysis results and propose a cross-validation approach for examining and comparing their calibration performance. Application is made to two clinical examples. In the first example, the joint probability that both sensitivity and specificity will be >80% in a new population is just 0.19, because of a low sensitivity. However, the summary PPV of 0.97 is high and calibrates well in new populations, with a probability of 0.78 that the true PPV will be at least 0.95. In the second example, post-test probabilities calibrate better when tailored to the prevalence in the new population, with cross-validation revealing a probability of 0.97 that the observed NPV will be within 10% of the predicted NPV.

What is the test's accuracy in my practice population? Tailored meta-analysis provides a plausible estimate

OBJECTIVES

Diagnostic test accuracy studies and meta-analyses may, in some cases, provide estimates that are highly improbable in practice; tailored meta-analysis provides a potential solution. To investigate the utility of tailored meta-analysis in synthesizing estimates of a test's accuracy compared with conventional meta-analysis for three case examples.

STUDY DESIGN AND SETTING

MEDLINE, Embase, and CINAHL were searched for relevant studies, and routine data were collected on the test positive rate and disease prevalence from the case settings to define an applicable region for each setting. Three cases were evaluated: mammography in the NHS Breast Screening Programme, Patient Health Questionnaire-9 to screen for depression in general practice, and Centor's criteria used to diagnose group A β-hemolytic streptococcus in general practice. For conventional meta-analysis, studies were selected using standard systematic review methods; for tailored meta-analysis, this selection was refined to those with results compatible with the applicable region for the setting.

RESULTS

In each example, studies were excluded as a result of incorporating an applicable region for the setting. Comparing tailored with conventional meta-analysis, the positive likelihood ratios (with 95% confidence intervals in brackets) were 36.5 (23.0, 57.9) and 19.8 (12.8, 30.9), respectively, for mammography and 4.89 (2.02, 11.8) and 2.35 (1.51, 3.67), respectively, for Centor's criteria. This had the effect of increasing the positive predictive value from 17% to 27% for mammography and 23% to 38% for Centor's criteria.

CONCLUSION

Tailored meta-analysis has the potential to provide a plausible estimate for a test's accuracy, which is specific to the practice setting. When compared with conventional meta-analysis, the difference may, in some cases, be sufficient to lead to different decisions on patient management.

Philosophy of science and the diagnostic process

This is an overview of the principles that underpin philosophy of science and how they may provide a framework for the diagnostic process. Although philosophy dates back to antiquity, it is only more recently that philosophers have begun to enunciate the scientific method. Since Aristotle formulated deduction, other modes of reasoning including induction, inference to best explanation, falsificationism, theory-laden observations and Bayesian inference have emerged. Thus, rather than representing a single overriding dogma, the scientific method is a toolkit of ideas and principles of reasoning. Here we demonstrate that the diagnostic process is an example of science in action and is therefore subject to the principles encompassed by the scientific method. Although a number of the different forms of reasoning are used readily by clinicians in practice, without a clear understanding of their pitfalls and the assumptions on which they are based, it leaves doctors open to diagnostic error. We conclude by providing a case example from the medico-legal literature in which diagnostic errors were made, to illustrate how applying the scientific method may mitigate the chance for diagnostic error.

Empirical evidence that disease prevalence may affect the performance of diagnostic tests with an implicit threshold: a cross-sectional study

OBJECTIVE

To investigate the effects that prevalence has on the diagnostic performance of junior doctors in interpreting x-rays.

DESIGN

Two-armed cross-sectional design using systematic sampling.

SETTING

Emergency department in the UK.

PARTICIPANTS

From a sample of 2593 patients (1434 men and 1159 women) taken from an unselected attending cohort between January and April 2002, 967 x-rays were analysed. The sex distribution was 558 men and 409 women, and the mean age of those receiving an x-ray was 34.6.

INTERVENTIONS

The interpretation of x-rays by junior doctors after their triage into high- and low-prevalence populations by radiographers.

MAIN OUTCOME MEASURES

Sensitivity, specificity, likelihood ratios, diagnostic odds ratios and receiver operator characteristic curve.

RESULTS

There were statistically significant differences in the performance characteristics of junior doctors when interpreting high-probability and low-probability x-rays. For the high- and low-probability populations, respectively, the sensitivities were 95.8% (95% CI 91.1% to 98.1%) and 78.3% (95% CI 65.7% to 87.2%) and the specificities were 56.0% (95% CI 41.9% to 69.2%) and 92.3% (95% CI 90.0% to 94.2%). Hierarchical logistic regression showed that the sensitivity did depend on the type of x-ray being interpreted but the diagnostic odds ratios did not vary significantly with prevalence, suggesting that doctors were changing their implicit threshold between the two populations along a common receiver operator characteristic curve.

CONCLUSIONS

This study provides evidence on how the prevalence may affect the performance of diagnostic tests with an implicit threshold and potentially includes the clinical history and examination. This has implications both for clinicians applying research findings to their practice and the design of future studies.

The assessment of the quality of reporting of meta-analyses in diagnostic research: a systematic review

Background

Over the last decade there have been a number of guidelines published, aimed at improving the quality of reporting in published studies and reviews. In systematic reviews this may be measured by their compliance with the PRISMA statement. This review aims to evaluate the quality of reporting in published meta-analyses of diagnostic tests, using the PRISMA statement and establish whether there has been a measurable improvement over time.

Methods

Eight databases were searched for reviews published prior to 31^st December 2008. Studies were selected if they evaluated a diagnostic test, measured performance, searched two or more databases, stated the search terms and inclusion criteria, and used a statistical method to summarise a test's performance. Data were extracted on the review characteristics and items of the PRISMA statement. To measure the change in the quality of reporting over time, PRISMA items for two periods of equal duration were compared.

Results

Compliance with the PRISMA statement was generally poor: none of the reviews completely adhered to all 27 checklist items. Of the 236 meta-analyses included following selection: only 2(1%) reported the study protocol; 59(25%) reported the searches used; 76(32%) reported the results of a risk of bias assessment; and 82(35%) reported the abstract as a structured summary. Only 11 studies were published before 2000. Thus, the impact of QUOROM on the quality of reporting was not evaluated. However, the periods 2001-2004 and 2005-2008 (covering 93% of studies) were compared using relative risks (RR). There was an increase in the proportion of reviews reporting on five PRISMA items: eligibility criteria (RR 1.13, 95% CI 1.00 - 1.27); risk of bias across studies (methods) (RR 1.81, 95% CI 1.34 - 2.44); study selection results (RR 1.48, 95% CI 1.05 - 2.09); results of individual studies (RR 1.37, 95% CI 1.09 - 1.72); risk of bias across studies (results) (RR 1.65, 95% CI 1.20 - 2.25).

Conclusion

Although there has been an improvement in the quality of meta-analyses in diagnostic research, there are still many deficiencies in the reporting which future reviewers need to address if readers are to trust the validity of the reported findings.

Uptake of newer methodological developments and the deployment of meta-analysis in diagnostic test research: a systematic review

BACKGROUND

The last decade has seen a number of methodological developments in meta-analysis of diagnostic test studies. However, it is unclear whether such developments have permeated the wider research community and on which applications they are being deployed. The objective was to assess the uptake and deployment of the main methodological developments in the meta-analysis of diagnostic tests, and identify the tests and target disorders most commonly evaluated by meta-analysis.

METHODS

Design--systematic review. Data Sources--Medline, EMBASE, CINAHL, Cochrane, PsychInfo, Global health, HMIC, and AMED were searched for studies published before 31st December 2008. Selection criteria--studies were included if they satisfied all of the following: evaluated a diagnostic test; measured test performance; searched two or more databases; stated search terms and inclusion criteria; used a statistical method to summarise performance. Data extraction--included the following data items: year; test; reference standard; target disorder; setting; statistical and quality methods.

RESULTS

236 studies were included. Over the last 5 years the number of meta-analyses published has increased, but the uptake of new statistical methods lags behind. Pooling the sensitivity and specificity and using the SROC remain the preferred methods for analysis in 70% of studies, with the bivariate random effects and HSROC model being used in only 22% and 5% of studies respectively. In contrast, between 2006 and 2008 the QUADAS tool was used in 40% of studies. Broadly, radiological imaging was the most frequent category of tests analysed (36%), with cancer (22%) and infection (21%) being the most common categories of target disorder. Nearly 80% of tests analysed were those normally used in specialist settings.

CONCLUSION

Although quality assessment in meta-analyses has improved with the introduction of QUADAS, uptake of the newer statistical methods is still lagging behind. Furthermore, the focus of secondary research seems to be in evaluating specialist tests in specialist settings, in contrast to the more routine tests and settings encountered in the majority of clinical practice.

Spectrum bias--why clinicians need to be cautious when applying diagnostic test studies

When applying study results to their practice, the clinician is constrained by a number of factors, perhaps none more important than spectrum bias, which describes the effect a change in patient case mix may have on the performance of a test. Although the literature contains notable examples of spectrum bias, the emphasis has been to demonstrate its existence and its implications on study design rather than how it affects the clinician. Here a definition is proposed before considering it from a GP's perspective. As a patient's probability of disease is in part determined by the test's result, having reliable estimates of a test's performance is imperative to making good decisions on patient management. Knowing how the test performs on a patient usually means knowing its performance within a particular subgroup. Unfortunately, studies tend to report weighted average estimates of performance across broad populations. Such estimates may be inaccurate at an individual level and at a population level with the overall performance of the test in practice varying significantly from the average estimate reported, owing to differing case mixes. To avert such problems, investigators should design studies to evaluate tests over all relevant subgroups, and where this is not possible, to be explicit about the case mix in the study sample. Furthermore, GPs should endeavour to know both individual patients and practice populations as a whole in terms of demographics and co-morbidities before applying study results to their patients.

How good are emergency department Senior House Officers at interpreting X-rays following radiographers?? triage?

OBJECTIVE

To assess the accuracy of Senior House Officers at interpreting plain X-rays following their triage by radiographers in an emergency department.

METHOD

We collected 2593 patients' records by systematic sampling of all those seen by emergency physicians between January 2002 and April 2002 (ca 10 000 patients) in a UK emergency department. The variables recorded included evidence of X-ray investigations and, when present, the Senior House Officer's diagnosis, the presence (abnormal) or absence of a radiographers red dot and the reference standard diagnosis. A separate category of uncertain (inconclusive) was applied to the Senior House Officer and reference standard diagnosis where appropriate. Diagnostic performance was measured by likelihood ratios with associated pre-test and post-test probabilities.

RESULTS

Including the uncertain category as abnormal gave the following results: there were 967 X-rays and those with a red dot had a probability of an abnormality of 80%. Although a further opinion of abnormal by a Senior House Officer increased this probability to 89% when they overrode the red dot opinion of the radiographer, it was incorrect in 26% of cases.

CONCLUSION

Currently, the Senior House Officer contributes to the red dot system by improving on the radiographer in rates of diagnosis of both abnormal and normal X-rays. Further reductions in error rates, however, are unlikely to be achieved until there is a change to the existing system. This may ultimately involve removing some of the responsibility of X-ray interpretation from the Senior House Officer. Any future research should consider the methodological issues highlighted by this study.

Cervical screening programmes: can automation help? Evidence from systematic reviews, an economic analysis and a simulation modelling exercise applied to the UK

OBJECTIVES

To assess the effectiveness and cost-effectiveness of adding automated image analysis to cervical screening programmes.

DATA SOURCES

Searching of all major electronic databases to the end of 2000 was supplemented by a detailed survey for unpublished UK literature.

METHOD

Four systematic reviews were conducted according to recognised guidance. The review of 'clinical effectiveness' included studies assessing reproducibility and impact on health outcomes and processes in addition to evaluations of test accuracy. A discrete event simulation model was developed, although the economic evaluation ultimately relied on a cost-minimisation analysis.

RESULTS

The predominant finding from the systematic reviews was the very limited amount of rigorous primary research. None of the included studies refers to the only commercially available automated image analysis device in 2002, the AutoPap Guided Screening (GS) System. The results of the included studies were debatably most compatible with automated image analysis being equivalent in test performance to manual screening. Concerning process, there was evidence that automation does lead to reductions in average slide processing times. In the PRISMATIC trial this was reduced from 10.4 to 3.9 minutes, a statistically significant and practically important difference. The economic evaluation tentatively suggested that the AutoPap GS System may be efficient. The key proviso is that credible data become available to support that the AutoPap GS System has test performance and processing times equivalent to those obtained for PAPNET.

CONCLUSIONS

The available evidence is still insufficient to recommend implementation of automated image analysis systems. The priority for action remains further research, particularly the 'clinical effectiveness' of the AutoPap GS System. Assessing the cost-effectiveness of introducing automation alongside other approaches is also a priority.

Effect of femoral fracture and intramedullary fixation on lung capillary leak

BACKGROUND

Pulmonary injury is an important complication in the trauma patient with long-bone fractures. The purpose of this study was to determine the effect of femoral fracture or fracture and intramedullary fixation on lung capillary leak. The contribution of leukocytes to lung injury in this model was also determined.

METHODS

The pulmonary capillary filtration coefficient was determined in lungs of rats after femur fracture or fracture and reamed or unreamed intramedullary fixation. Pulmonary arterial vascular resistance and lung neutrophil content were also determined.

RESULTS

Fracture alone did not cause lung injury, whereas fracture and intramedullary fixation elicited lung capillary leak. Fracture alone and intramedullary fixation increased pulmonary vascular resistance, whereas unreamed intramedullary fixation caused lung leukosequestration.

CONCLUSION

Femoral fracture alone does not cause an increase in pulmonary microvascular permeability. Femoral fracture and intramedullary fixation causes lung capillary leak, which is not increased by reaming the femoral canal.

Aspiration of activated charcoal elicits an increase in lung microvascular permeability

BACKGROUND

Gastric decontamination with orally administered activated charcoal is the recommended treatment for many poisonings. However, ingestion of central nervous system depressants resulting in loss of protective airway reflexes may result in pulmonary aspiration of activated charcoal. Although activated charcoal has been reported to be an inert substance, evidence suggests that pulmonary aspiration of charcoal is associated with lung edema formation and pulmonary compromise. This study tested the hypothesis that intratracheal instillation of activated charcoal disrupts the integrity of the lung microvascular barrier.

METHODS

The capillary filtration coefficient (Kf,c), a sensitive measure of lung microvascular permeability, was determined isogravimetrically prior to and after intratracheal instillation of activated charcoal 0.04 g/kg (12% weight/vol solution, pH 7.4) or an equal volume of sterile water in isolated, perfused rat lungs. Arterial blood gas analysis was determined prior to and after tracheal instillation of activated charcoal or sterile water in a separate group of animals.

RESULTS

Intratracheal instillation of activated charcoal resulted in a significant increase in pulmonary microvascular permeability compared to lungs treated with sterile water or control lungs (delta Kf,c = +0.21 +/- 0.076; -0.014 +/- 0.04; and -0.041 +/- 0.02 mL/min/cm H2O/100 g lung tissue, respectively, p < 0.05 ANOVA). There was no significant difference in baseline blood gases in the 3 experimental groups. There was a significant decrease in arterial Po2, bicarbonate, and pH in animals administered activated charcoal compared to time-matched controls and animals administered sterile water.

CONCLUSIONS

Intratracheal instillation of activated charcoal is associated with a significant increase in lung microvascular permeability and arterial blood gas derangements. The effects of activated charcoal on pulmonary microvascular barrier integrity may contribute to the lung edema formation and pulmonary compromise observed following clinical aspiration of activated charcoal.

Neutrophil elastase promotes lung microvascular injury and proteolysis of endothelial cadherins

Intestinal ischemia-reperfusion (I-R) is associated with lung injury and the acute respiratory distress syndrome. The hypothesis of this study was that intestinal I-R activates circulating neutrophils to promote elastase-mediated lung injury. Isolated rat lungs were perfused with blood or plasma obtained after intestinal I-R, and lung neutrophil retention and injury and bronchoalveolar lavage (BAL) elastase were measured. Perfusion with I-R blood caused lung neutrophil accumulation and injury and increased BAL elastase. These effects were attenuated by the elastase inhibitor L-658758. Interference with neutrophil adherence before gut reperfusion blocked BAL elastase accumulation. The role of endothelial junction proteins (cadherins) in I-R-elicited lung damage was also evaluated. Activated human neutrophils proteolyzed cadherins in human umbilical vein endothelial cells. Furthermore, plasma of patients with acute respiratory distress syndrome contained soluble cadherin fragments. The results of this study suggest that the elastase released by systemically activated neutrophils contributes to lung neutrophil accumulation and pulmonary microvascular injury. Elastase-mediated proteolysis of endothelial cell cadherins may represent the mechanism through which lung microvascular integrity is disrupted after intestinal I-R.

An experimental study of lumbar destabilization. Restabilization and bone density

STUDY DESIGN

An investigation of the effects of bone density on lumbar spine stability using destabilizing and restabilizing procedures.

OBJECTIVES

To measure cadaveric vertebral bone densities computed tomographic scans and to correlate the measured densities with lumbar spine stability in the intact and during sequential destabilization and restabilization.

SUMMARY OF BACKGROUND DATA

The stabilizing effects of lumbar pedicle screw fixation have been widely described. Numerous construct failure mechanisms have been observed, including screw loosening in osteoporosis. Although previous studies have analyzed the effect of bone density on the compression strength of bone similar to that used in interbody fusion and the relationship of pedicle screw pull-out strength to vertebral bone density, a combined study of bone density and construct stability using an interbody bone spacer with pedicle fixation has not been performed.

METHODS

Bone densities were measured in 20 human cadaveric lumbar spines using computed tomography scans and a hydroxyapatite phantom. After the specimens were mounted in a testing frame, the L4-L5 motion segments were subjected to cyclic axial compression-torsional loads, and axial and rotational intervertebral displacements were monitored. Laminectomy, facetectomy, and pedicle screw-plate fixation were performed sequentially in three specimens. Ten others underwent these procedures with an additional destabilization procedure, discectomy, after facetectomy. Seven others underwent the same sequence as the previous group, followed by the insertion of interbody bone. Cyclic testing was resumed after each procedure.

RESULTS

Average bone densities varied widely among the specimens. Average bone densities of the pedicle and of the vertebral body for individual specimens were well-correlated (r = 0.897). Displacements were recorded as a percentage of the intact state before destabilization; average percentages are reported as follows: axial displacements increased after facetectomy (145%) and subsequent discectomy (251%), and rotational displacements increased after facetectomy (295%) and discectomy (390%). Instrumentation without interbody bone resulted in specimens with decreased axial (126%) and rotational (156%) displacements. The addition of interbody bone further decreased axial (111%) and rotational (117%) displacements. The rotational stabilization provided by instrumentation was well-correlated with vertebral bone density (r = 0.804). This correlation was enhanced by the use of interbody bone (r = 0.939).

CONCLUSION

The unstable lumbar spine can be partially stabilized using fixation. Interbody bone provides additional stability. The immediate stability provided by pedicle screws is greater in lumbar vertebrae with higher bone density.

Complement-mediated lung injury and neutrophil retention after intestinal ischemia-reperfusion

Complement-mediated neutrophil activation appears to play an important role in ischemia-reperfusion (I/R) injury in a variety of tissues, including the heart, lung, and small bowel. The objective of this study was to determine whether inhibition of the alternative and classic complement cascades by administration of soluble complement receptor 1 (sCR1) prevents the increased neutrophil stiffness, lung neutrophil retention, and pulmonary microvascular injury elicited by a systemic inflammatory insult. Isolated lungs were perfused with blood obtained from animals subjected to 2 h of intestinal ischemia and 20 min of reperfusion (I/R) or control (nonischemic) surgery. Intestinal I/R resulted in a significant increase in neutrophil stiffness, lung neutrophil retention, and increased pulmonary microvascular permeability, effects that were prevented by administration of sCR1 before intestinal reperfusion. The results of this study suggest that I/R injury in the gut is a potent systemic inflammatory stimulus that induces complement-mediated neutrophil stiffness, lung neutrophil entrapment, and pulmonary microvascular dysfunction.

Lack of weight gain of sheep following iodine supplementation in inland regions of the South Island

Weight gain response to iodine supplementation was investigated in five groups of sheep in different seasons. In only one spring period in one trial was a significant response obtained.