Computationally efficient methods for fitting mixed models to electronic health records data

Motivated by two case studies using primary care records from the Clinical Practice Research Datalink, we describe statistical methods that facilitate the analysis of tall data, with very large numbers of observations. Our focus is on investigating the association between patient characteristics and an outcome of interest, while allowing for variation among general practices. We explore ways to fit mixed-effects models to tall data, including predictors of interest and confounding factors as covariates, and including random intercepts to allow for heterogeneity in outcome among practices. We introduce (1) weighted regression and (2) meta-analysis of estimated regression coefficients from each practice. Both methods reduce the size of the dataset, thus decreasing the time required for statistical analysis. We compare the methods to an existing subsampling approach. All methods give similar point estimates, and weighted regression and meta-analysis give similar standard errors for point estimates to analysis of the entire dataset, but the subsampling method gives larger standard errors. Where all data are discrete, weighted regression is equivalent to fitting the mixed model to the entire dataset. In the presence of a continuous covariate, meta-analysis is useful. Both methods are easy to implement in standard statistical software.

Label-invariant models for the analysis of meta-epidemiological data

Rich meta‐epidemiological data sets have been collected to explore associations between intervention effect estimates and study‐level characteristics. Welton et al proposed models for the analysis of meta‐epidemiological data, but these models are restrictive because they force heterogeneity among studies with a particular characteristic to be at least as large as that among studies without the characteristic. In this paper we present alternative models that are invariant to the labels defining the 2 categories of studies. To exemplify the methods, we use a collection of meta‐analyses in which the Cochrane Risk of Bias tool has been implemented. We first investigate the influence of small trial sample sizes (less than 100 participants), before investigating the influence of multiple methodological flaws (inadequate or unclear sequence generation, allocation concealment, and blinding). We fit both the Welton et al model and our proposed label‐invariant model and compare the results. Estimates of mean bias associated with the trial characteristics and of between‐trial variances are not very sensitive to the choice of model. Results from fitting a univariable model show that heterogeneity variance is, on average, 88% greater among trials with less than 100 participants. On the basis of a multivariable model, heterogeneity variance is, on average, 25% greater among trials with inadequate/unclear sequence generation, 51% greater among trials with inadequate/unclear blinding, and 23% lower among trials with inadequate/unclear allocation concealment, although the 95% intervals for these ratios are very wide. Our proposed label‐invariant models for meta‐epidemiological data analysis facilitate investigations of between‐study heterogeneity attributable to certain study characteristics.

Is Achenbach's syndrome a surgical emergency? A systematic review

AIM

The aim of this study is to establish the nature (urgent vs. non-urgent), demographics, presentation and management of Achenbach's syndrome and to formulate an algorithmic approach for their diagnosis and management.

MATERIALS AND METHODS

A systematic review and met-aggregation of literature from 1944 to 2015 in English language in MedLine, Embase and Cochrane database were conducted.

RESULTS

Achenbach's syndrome is a female-dominant disease with median age of 49.5 years (range 22-76) (age ≤60, n = 11/12, 91 %). It presents with unilateral volar discoloration of a finger (100 %). It is associated with pain (n = 7/12, 58. %), edema (n = 7/12, 58 %), and paresthesia (n = 3/12, 25 %). The median time to resolution of symptoms without any intervention was 4 days (range 2-14).

CONCLUSION

AS is self-limiting and a non-urgent surgical condition. It can be differentiated from other pathologies by clinical spectrum, patient demographics and in doubtful circumstances (acute limb ischemia) by Doppler sonography. An algorithmic approach can avoid hospital admissions, partially unnecessary investigation and assist in patient assurance.

A test of insulator interactions in Drosophila

Insulators are a class of elements that define independent domains of gene function. The Drosophila gypsy insulator is proposed to establish regulatory isolation by forming loop domains that constrain interactions between transcriptional control elements. This supposition is based upon the observation that insertion of a single gypsy insulator between an enhancer and promoter blocks enhancer function, while insertion of two gypsy insulators promotes enhancer bypass and activation of transcription. To investigate this model, we determined whether non-gypsy insulators interacted with each other and with the gypsy insulator. Pairs of scs or scs' insulators blocked enhancer function. Further, an intervening scs insulator did not block gypsy insulator interactions. Taken together, these data suggest that not all Drosophila insulators interact, with this property restricted to some insulators, such as gypsy. Three gypsy insulators inserted between an enhancer and promoter blocked enhancer function, indicating that gypsy insulator interactions may be restricted to pairs. Our studies imply that formation of loop domains may represent one of many mechanisms used by insulators to impart regulatory isolation.

Amyloidosis in Vanuatu

Thirteen cases of amyloidosis are reported from Vanuatu between 1983 and 1985. There appears to be a high incidence of the disease similar to that found in Papua New Guinea. The role of malaria as an aetiological agent is discussed although most cases had a history of past or active tuberculosis. Most patients presented as either nephrotic syndrome or a syndrome of abdominal pain, diarrhoea, weight loss and proteinuria.

Effects of mitral valve surgery on static lung function and exercise performance

Lung function at rest was assessed in 50 patients before and six months after mitral valve surgery. There were small increases in spirometric volumes (FEV1 and vital capacity) with decreases in total lung capacity and residual volume, but no change in carbon monoxide transfer factor or transfer coefficient (KCO). Progressive exercise tests performed before and after operation in 19 of the patients confirmed an improved exercise capacity after surgery. The patients with the greatest symptomatic improvement in breathlessness were also those who achieved the greatest increase in maximum work load and the greatest decrease in ventilation for a given oxygen consumption. Depression of the ST segment of the electrocardiogram and frequent ventricular ectopic beats on exercise remained common after surgery and may have been due to digoxin treatment.

Relation between severity of mitral valve disease and results of routine lung function tests in non-smokers

The effects of mitral valve disease on lung function have been studied in 26 non-smoking patients by relating values for lung volumes and carbon monoxide transfer factor (TLCO) to various indices of cardiac function measured at catheterisation. In general, more severe mitral disease was associated with greater abnormalities of lung function. Reductions of the one-second forced expiratory volume, vital capacity, TLCO and transfer coefficient, and increase in residual volume were all significantly related to the severity of mitral valve disease. In addition, the cardiothoracic ratio, measured radiographically, showed an inverse correlation with both vital capacity and total lung capacity. Although some of the consequences of mitral valve disease on lung function resemble those of primary airway disease, useful distinguishing points are the relative normality of the forced expiratory ratio and the absence of an increase in total lung capacity.