Reporting of occupational and environmental research: use and misuse of statistical and epidemiological methods

Mercury levels in human hair in South India: baseline, artisanal goldsmiths and coal-fired power plants

India is a major emitter of mercury to the environment, mainly due to emissions from coal-fired power plants. Consumption of fish and rice, two important pathways for human exposure to mercury, is particularly high in South India. Here, we report concentrations of total mercury in hair (THg_hair) in 668 participants from South India. Three cities were covered: (i) a city on the east coast with four active coal-fired thermal power plants (Nellore), (ii) a city on the west coast with no major mercury source (Vasco da Gama), and (iii) a metropolitan city in the interior with no major mercury source (Hyderabad). Geometric mean of THg_hair of the entire study population is 0.14 µg/g (95% confidence interval, CI: 0.13-0.15 µg/g). Significant predictor variables are age, fish consumption, and occupations such as dental studies, subsistence fishing, and artisanal goldsmithing (which is different from artisanal scale gold mining). Our results support the hypothesis that people living in a city with active coal-fired power plants may have higher THg_hair than those in cities with no major mercury source.

[Recent Epidemiological Studies on Methylmercury, Mercury and Selenium]

More than sixty years has passed since the outbreak of Minamata disease, and high-level methylmercury contaminations now seem nonexistent in Japan. However, mercury has been continuously discharged from natural sources and industrial activities, and the health effects on children susceptible to methylmercury exposure at low levels, in addition to mercury contamination from mercury or gold mining areas in developing countries, become a worldwide concern. In this article, we provide a recent overview of epidemiological studies regarding methylmercury and mercury. The following findings were obtained. (1) Many papers on exposure assessment of methylmercury/mercury have been published since the Minamata Convention on Mercury was adopted in 2013. (2) The most crucial problem is child developmental neurotoxicity resulting from prenatal exposure to methylmercury, but its precise assessment seems to be difficult because most of such effects are neither severe nor specific. (3) Several problems raised in birth cohort studies (e.g., whether IQ deficits due to prenatal methylmercury exposure remain when the children become adults, or whether the postnatal exposure at low levels also causes such adverse effects in children) remain unsolved. (4) Concurrent exposure models of methylmercury, lead, polychlorinated biphenyls, aresenic, and organochlorine pesticides, as well as possible antagonists such as polyunsaturated fatty acids and selenium, should be considered in the study design because the exposure levels of methylmercury are extremely low in developed countries. (5) Further animal experiments and molecular biological studies, in addition to human studies, are required to clarify the mechanism of methylmercury toxicity.

STRengthening analytical thinking for observational studies: the STRATOS initiative

The validity and practical utility of observational medical research depends critically on good study design, excellent data quality, appropriate statistical methods and accurate interpretation of results. Statistical methodology has seen substantial development in recent times. Unfortunately, many of these methodological developments are ignored in practice. Consequently, design and analysis of observational studies often exhibit serious weaknesses. The lack of guidance on vital practical issues discourages many applied researchers from using more sophisticated and possibly more appropriate methods when analyzing observational studies. Furthermore, many analyses are conducted by researchers with a relatively weak statistical background and limited experience in using statistical methodology and software. Consequently, even 'standard' analyses reported in the medical literature are often flawed, casting doubt on their results and conclusions. An efficient way to help researchers to keep up with recent methodological developments is to develop guidance documents that are spread to the research community at large. These observations led to the initiation of the strengthening analytical thinking for observational studies (STRATOS) initiative, a large collaboration of experts in many different areas of biostatistical research. The objective of STRATOS is to provide accessible and accurate guidance in the design and analysis of observational studies. The guidance is intended for applied statisticians and other data analysts with varying levels of statistical education, experience and interests. In this article, we introduce the STRATOS initiative and its main aims, present the need for guidance documents and outline the planned approach and progress so far. We encourage other biostatisticians to become involved.

Strengthening the Reporting of Observational Studies in Epidemiology (STROBE): explanation and elaboration

Much medical research is observational. The reporting of observational studies is often of insufficient quality. Poor reporting hampers the assessment of the strengths and weaknesses of a study and the generalisability of its results. Taking into account empirical evidence and theoretical considerations, a group of methodologists, researchers, and editors developed the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) recommendations to improve the quality of reporting of observational studies. The STROBE Statement consists of a checklist of 22 items, which relate to the title, abstract, introduction, methods, results and discussion sections of articles. Eighteen items are common to cohort studies, case-control studies and cross-sectional studies and four are specific to each of the three study designs. The STROBE Statement provides guidance to authors about how to improve the reporting of observational studies and facilitates critical appraisal and interpretation of studies by reviewers, journal editors and readers. This explanatory and elaboration document is intended to enhance the use, understanding, and dissemination of the STROBE Statement. The meaning and rationale for each checklist item are presented. For each item, one or several published examples and, where possible, references to relevant empirical studies and methodological literature are provided. Examples of useful flow diagrams are also included. The STROBE Statement, this document, and the associated Web site (http://www.strobe-statement.org/) should be helpful resources to improve reporting of observational research.

Mortality and cancer incidence in a copper-zinc cohort

Previous studies of copper-zinc workers have primarily observed significant increases in lung and other respiratory cancers. This study concurrently examined cancer incidence and cause-specific mortality for a cohort of workers at a copper-zinc producer in Ontario, Canada, from 1964 to 2005. Significant elevations in lung cancer incidence were observed for males in the overall cohort (standardized incidence ratio [SIR] = 124, 95% confidence interval [CI] = 102-150) and for surface mine (SIR = 272, 95% CI = 124-517), concentrator (SIR = 191, 95% CI = 102-327), and central maintenance (SIR = 214, 95% CI = 125-343) employees. Significant elevations of non-Hodgkin's lymphoma incidence were observed for male underground mine employees (SIR = 232, 95% CI = 111-426). Occupational etiology cannot be ascertained with the current exploratory study design. Future studies could (1) incorporate exposure assessment for subgroups within the existing cohort and (2) determine the efficacy of wellness programs in partnership with the local health unit.

Mortality and cancer incidence in a copper-zinc cohort

Previous studies of copper-zinc workers have primarily observed significant increases in lung and other respiratory cancers. This study concurrently examined cancer incidence and cause-specific mortality for a cohort of workers at a copper-zinc producer in Ontario, Canada, from 1964 to 2005. Significant elevations in lung cancer incidence were observed for males in the overall cohort (standardized incidence ratio [SIR] = 124, 95% confidence interval [CI] = 102-150) and for surface mine (SIR = 272, 95% CI = 124-517), concentrator (SIR = 191, 95% CI = 102-327), and central maintenance (SIR = 214, 95% CI = 125-343) employees. Significant elevations of non-Hodgkin's lymphoma incidence were observed for male underground mine employees (SIR = 232, 95% CI = 111-426). Occupational etiology cannot be ascertained with the current exploratory study design. Future studies could (1) incorporate exposure assessment for subgroups within the existing cohort and (2) determine the efficacy of wellness programs in partnership with the local health unit.

Quality of reporting statistics in two Indian pharmacology journals

OBJECTIVE

To evaluate the reporting of the statistical methods in articles published in two Indian pharmacology journals.

MATERIALS AND METHODS

All original articles published since 2002 were downloaded from the journals' (Indian Journal of Pharmacology (IJP) and Indian Journal of Physiology and Pharmacology (IJPP)) website. These articles were evaluated on the basis of appropriateness of descriptive statistics and inferential statistics. Descriptive statistics was evaluated on the basis of reporting of method of description and central tendencies. Inferential statistics was evaluated on the basis of fulfilling of assumption of statistical methods and appropriateness of statistical tests. Values are described as frequencies, percentage, and 95% confidence interval (CI) around the percentages.

RESULTS

Inappropriate descriptive statistics was observed in 150 (78.1%, 95% CI 71.7-83.3%) articles. Most common reason for this inappropriate descriptive statistics was use of mean ± SEM at the place of "mean (SD)" or "mean ± SD." Most common statistical method used was one-way ANOVA (58.4%). Information regarding checking of assumption of statistical test was mentioned in only two articles. Inappropriate statistical test was observed in 61 (31.7%, 95% CI 25.6-38.6%) articles. Most common reason for inappropriate statistical test was the use of two group test for three or more groups.

CONCLUSION

Articles published in two Indian pharmacology journals are not devoid of statistical errors.

Testicular dysgenesis syndrome and the estrogen hypothesis: a quantitative meta-analysis

Male reproductive tract abnormalities such as hypospadias and cryptorchidism, and testicular cancer have been proposed to comprise a common syndrome together with impaired spermatogenesis with a common etiology resulting from the disruption of gonadal development during fetal life, the testicular dysgenesis syndrome (TDS). The only quantitative summary estimate of the link between prenatal exposure to estrogenic agents and testicular cancer was published over 10 years ago; other reviews of the link between estrogenic compounds, other than the potent pharmaceutical estrogen diethylstilbestrol (DES), and TDS end points have remained inconclusive. We conducted a quantitative meta-analysis of the association between the end points related to TDS and prenatal exposure to estrogenic agents. Inclusion in this analysis was based on mechanistic criteria, and the plausibility of an estrogen receptor (ER)-alpha-mediated mode of action was specifically explored. Eight studies were included, investigating the etiology of hypospadias and/or cryptorchidism that had not been identified in previous systematic reviews. Four additional studies of pharmaceutical estrogens yielded a statistically significant updated summary estimate for testicular cancer. Results of the subset analyses point to the existence of unidentified sources of heterogeneity between studies or within the study population.

[Strengthening the reporting of observational studies in epidemiology (STROBE): explanation and elaboration]

Much medical research is observational. The reporting of observational studies is often of insufficient quality. Poor reporting hampers the assessment of the strengths and weaknesses of a study and the generalisability of its results. Taking into account empirical evidence and theoretical considerations, a group of methodologists, researchers, and editors developed the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) recommendations to improve the quality of reporting of observational studies. The STROBE Statement consists of a checklist of 22 items, which relate to the title, abstract, introduction, methods, results and discussion sections of articles. Eighteen items are common to cohort studies, case-control studies and cross-sectional studies and four are specific to each of the three study designs. The STROBE Statement provides guidance to authors about how to improve the reporting of observational studies and facilitates critical appraisal and interpretation of studies by reviewers, journal editors and readers. This explanatory and elaboration document is intended to enhance the use, understanding, and dissemination of the STROBE Statement. The meaning and rationale for each checklist item are presented. For each item, one or several published examples and, where possible, references to relevant empirical studies and methodological literature are provided. Examples of useful flow diagrams are also included. The STROBE Statement, this document, and the associated Web site (http://www.strobe-statement.org/) should be helpful resources to improve reporting of observational research.

A Review of the Relationship Between 100% Fruit Juice Consumption and Weight in Children and Adolescents

Studies assessing a relationship between consumption of 100% fruit juice by children and adolescents and weight are contradictory. The purpose of this review was to assess the 9 cross-sectional and 12 longitudinal studies that have looked at this association. Of the 9 cross-sectional studies reviewed, only 3 reported any association. Those studies used small, local convenience samples of preschool children; furthermore, selection criteria were not well defined. One found that preschool children consuming ≥ 12 fluid oz/day of 100% fruit juice had a higher prevalence of overweight than those who consumed less than 12 oz/day (32% vs 9%). Later, a separate study showed that this relationship held only for apple juice. Another study demonstrated an association of overweight and energy from juice. These 3 studies were not nationally representative. Only 3 of the longitudinal studies showed an association between 100% fruit juice consumption and weight; 1 found an association only in adolescent girls, and 2 reported an association in children who were already overweight. None of the longitudinal studies was nationally representative, but 5 had sample sizes of at least 1000, 2 were ethnically diverse, and 3 had geographically separate sites, suggesting that the findings could be applicable to wider populations. Based on the currently available evidence, it can be concluded that there is no systematic association between consumption of 100% fruit juice and overweight in children or adolescents. Data do support consumption of 100% fruit juice in moderate amounts and suggest that consumption of 100% fruit juice may be an important strategy to help children meet the current recommendations for fruit.

Testicular dysgenesis syndrome and the estrogen hypothesis: a quantitative meta-analysis

BACKGROUND

Male reproductive tract abnormalities such as hypospadias and cryptorchidism, and testicular cancer have been proposed to comprise a common syndrome together with impaired spermatogenesis with a common etiology resulting from the disruption of gonadal development during fetal life, the testicular dysgenesis syndrome (TDS). The hypothesis that in utero exposure to estrogenic agents could induce these disorders was first proposed in 1993. The only quantitative summary estimate of the association between prenatal exposure to estrogenic agents and testicular cancer was published over 10 years ago, and other systematic reviews of the association between estrogenic compounds, other than the potent pharmaceutical estrogen diethylstilbestrol (DES), and TDS end points have remained inconclusive.

OBJECTIVES

We conducted a quantitative meta-analysis of the association between the end points related to TDS and prenatal exposure to estrogenic agents. Inclusion in this analysis was based on mechanistic criteria, and the plausibility of an estrogen receptor (ER)-alpha-mediated mode of action was specifically explored.

RESULTS

We included in this meta-analysis eight studies investigating the etiology of hypospadias and/or cryptorchidism that had not been identified in previous systematic reviews. Four additional studies of pharmaceutical estrogens yielded a statistically significant updated summary estimate for testicular cancer.

CONCLUSIONS

The doubling of the risk ratios for all three end points investigated after DES exposure is consistent with a shared etiology and the TDS hypothesis but does not constitute evidence of an estrogenic mode of action. Results of the subset analyses point to the existence of unidentified sources of heterogeneity between studies or within the study population.

Strengthening the Reporting of Observational Studies in Epidemiology (STROBE): explanation and elaboration

Much medical research is observational. The reporting of observational studies is often of insufficient quality. Poor reporting hampers the assessment of the strengths and weaknesses of a study and the generalisability of its results. Taking into account empirical evidence and theoretical considerations, a group of methodologists, researchers, and editors developed the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) recommendations to improve the quality of reporting of observational studies. The STROBE Statement consists of a checklist of 22 items, which relate to the title, abstract, introduction, methods, results and discussion sections of articles. Eighteen items are common to cohort studies, case-control studies and cross-sectional studies and four are specific to each of the three study designs. The STROBE Statement provides guidance to authors about how to improve the reporting of observational studies and facilitates critical appraisal and interpretation of studies by reviewers, journal editors and readers. This explanatory and elaboration document is intended to enhance the use, understanding, and dissemination of the STROBE Statement. The meaning and rationale for each checklist item are presented. For each item, one or several published examples and, where possible, references to relevant empirical studies and methodological literature are provided. Examples of useful flow diagrams are also included. The STROBE Statement, this document, and the associated Web site (http://www.strobe-statement.org/) should be helpful resources to improve reporting of observational research.

Selection in reported epidemiological risks: an empirical assessment

BACKGROUND

Epidemiological studies may be subject to selective reporting, but empirical evidence thereof is limited. We empirically evaluated the extent of selection of significant results and large effect sizes in a large sample of recent articles.

METHODS AND FINDINGS

We evaluated 389 articles of epidemiological studies that reported, in their respective abstracts, at least one relative risk for a continuous risk factor in contrasts based on median, tertile, quartile, or quintile categorizations. We examined the proportion and correlates of reporting statistically significant and nonsignificant results in the abstract and whether the magnitude of the relative risks presented (coined to be consistently > or =1.00) differs depending on the type of contrast used for the risk factor. In 342 articles (87.9%), > or =1 statistically significant relative risk was reported in the abstract, while only 169 articles (43.4%) reported > or =1 statistically nonsignificant relative risk in the abstract. Reporting of statistically significant results was more common with structured abstracts, and was less common in US-based studies and in cancer outcomes. Among 50 randomly selected articles in which the full text was examined, a median of nine (interquartile range 5-16) statistically significant and six (interquartile range 3-16) statistically nonsignificant relative risks were presented (p = 0.25). Paradoxically, the smallest presented relative risks were based on the contrasts of extreme quintiles; on average, the relative risk magnitude was 1.41-, 1.42-, and 1.36-fold larger in contrasts of extreme quartiles, extreme tertiles, and above-versus-below median values, respectively (p < 0.001).

CONCLUSIONS

Published epidemiological investigations almost universally highlight significant associations between risk factors and outcomes. For continuous risk factors, investigators selectively present contrasts between more extreme groups, when relative risks are inherently lower.

How to make your article more acceptable for the statistical reviewer

Many medical articles have problems with methodological aspects. To help prevent this, medical statisticians should be more involved in all aspects of medical research. Having more statistical reviewing of manuscripts submitted to journals should also help, but will not cure the problem. This paper makes some suggestions that may help authors make manuscripts more acceptable methodologically, but there is no substitute for statistical involvement throughout the research process. Neurourol. Urodynam. 26:318-322, 2007. (c) 2007 Wiley-Liss, Inc.

Evidence-based medicine: assessment of knowledge of basic epidemiological and research methods among medical doctors

BACKGROUND

An understanding of statistical methods and basic epidemiology are crucial for the practice of modern medicine.

AIMS

To assess (1) the knowledge of basic methods of conducting research and data analysis among residents and practicing doctors and (2) the effect of country of medical school graduation, professional status, medical article reading and writing experience on the level of this knowledge.

METHODS

Data were collected by means of a supervised self-administered questionnaire, which was distributed among doctors at Soroka Medical Center, Beer-Sheva, Israel. The questionnaire included 10 multiple-choice questions on basic epidemiology and statistics, and respondent demographical data.

RESULTS

Of the 260 eligible doctors, 219 (84.2%) returned completed questionnaires. Of the 219 doctors, 50% graduated more than 8.5 years ago, 39.7% were specialists and the remaining were residents. The most frequent specialty was internal medicine (37.4%). Israel was the most frequent country of graduation (45.7%), followed by the former Soviet Union (Eastern medical education; 38.4%). The median total score of knowledge was 4 of 10 questions (interquartile range 2-6). A higher score was associated with a Western medical education, being a specialist, shorter elapsed time since graduation, higher number of publications and self-reported reading of "methods" and "discussion" sections in scientific articles.

CONCLUSION

This study found a low level of knowledge of basic principles of research methods and data analysis among doctors, and this knowledge considerably differed by country of medical school graduation.

Risk estimation for carcinogens based on epidemiological data: A structured approach, illustrated by an example on chromium

It is generally recognized that human, epidemiological data, if available, are preferred as the starting point for quantitative risk analysis above the use of data from animal studies. Although methods to obtain proper risk estimates from epidemiological data are available, several impediments prevent their widespread application. These impediments include unfamiliarity with epidemiological methods and the lack of a structured and transparent approach. We described a framework to conduct quantitative cancer risk assessment based on epidemiological studies in a structured, transparent, and reproducible manner. Important features of the process include a weight-of-the-evidence approach, estimation of the optimal exposure-risk function by fitting a regression model to the epidemiological data, estimation of uncertainty introduced by potential biases and missing information in the epidemiological studies, and calculation of excess lifetime risk through a life table to take into account competing risks. Sensitivity analyses are a useful tool to obtain insight into the impact of assumptions made and the variability of the underlying data. The framework is sufficiently flexible to allow many types of data, ranging from published, sometimes incomplete data to detailed individual data, while maintaining an optimal result, i.e., a state-of-the-art risk estimate with confidence intervals, based on all available evidence of sufficient quality.

Appraising the quality of randomized controlled trials: inter-rater reliability for the OTseeker evidence database

RATIONALE AND AIMS

'OTseeker' is an online database of randomized controlled trials (RCTs) and systematic reviews relevant to occupational therapy. RCTs are critically appraised and rated for quality using the 'PEDro' scale. We aimed to investigate the inter-rater reliability of the PEDro scale before and after revising rating guidelines.

METHODS

In study 1, five raters scored 100 RCTs using the original PEDro scale guidelines. In study 2, two raters scored 40 different RCTs using revised guidelines. All RCTs were randomly selected from the OTseeker database. Reliability was calculated using Kappa and intraclass correlation coefficients [ICC (model 2,1)].

RESULTS

Inter-rater reliability was 'good to excellent' in the first study (Kappas >or= 0.53; ICCs >or= 0.71). After revising the rating guidelines, the reliability levels were equivalent or higher to those previously obtained (Kappas >or= 0.53; ICCs >or= 0.89), except for the item, 'groups similar at baseline', which still had moderate reliability (Kappa = 0.53). In study 2, two PEDro scale items, which had their definitions revised, 'less than 15% dropout' and 'point measures and variability', showed higher reliability. In both studies, the PEDro items with the lowest reliability were 'groups similar at baseline' (Kappas = 0.53), 'less than 15% dropout' (Kappas <or= 0.68) and 'point measures and variability data' (Kappas <or= 0.68).

CONCLUSION

The PEDro scale is a reliable instrument for rating the quality of RCTs. Revised rating guidelines are provided for scale items that are difficult to rate, and helped to improve inter-rater reliability.

Issues in the reporting of epidemiological studies: a survey of recent practice

OBJECTIVES

To review current practice in the analysis and reporting of epidemiological research and to identify limitations.

DESIGN

Examination of articles published in January 2001 that investigated associations between risk factors/exposure variables and disease events/measures in individuals.

SETTING

Eligible English language journals including all major epidemiological journals, all major general medical journals, and the two leading journals in cardiovascular disease and cancer.

MAIN OUTCOME MEASURE

Each article was evaluated with a standard proforma.

RESULTS

We found 73 articles in observational epidemiology; most were either cohort or case-control studies. Most studies looked at cancer and cardiovascular disease, even after we excluded specialty journals. Quantitative exposure variables predominated, which were mostly analysed as ordered categories but with little consistency or explanation regarding choice of categories. Sample selection, participant refusal, and data quality received insufficient attention in many articles. Statistical analyses commonly used odds ratios (38 articles) and hazard/rate ratios (23), with some inconsistent use of terminology. Confidence intervals were reported in most studies (68), though use of P values was less common (38). Few articles explained their choice of confounding variables; many performed subgroup analyses claiming an effect modifier, though interaction tests were rare. Several investigated multiple associations between exposure and outcome, increasing the likelihood of false positive claims. There was evidence of publication bias.

CONCLUSIONS

This survey raises concerns regarding inadequacies in the analysis and reporting of epidemiological publications in mainstream journals.

Systematic review of fibroadenoma as a risk factor for breast cancer

Fibroadenoma (FA) is a common breast lesion occurring in 25% of asymptomatic women. Several studies considered FA as a risk factor for breast cancer, prompting a systematic review of the literature. We selected cohort and case-control studies. Seven studies satisfied the selection criteria. Dupont et al. (1994) and McDivitt et al. (1992) were considered to provide the strongest evidence, showing the relative risk for excised FA without hyperplasia in the range 1.48-1.7, with hyperplasia 3.47-3.7, and with hyperplasia and atypia 6.9-7.29, persisting for more than 20 years. Five studies by Levi et al. (1994), Ciatto et al. (1997), Moskowitz et al. (1980), Carter et al. (1988), and Levshin et al. (1998), were considered to provide weaker evidence, although they showed similar results. None of the results could be used to quantify the risks of excised, non-excised, and asymptomatic FA. More care should be taken in managing patients with complex FAs and FAs with hyperplasia with or without atypia. Core biopsy may be a better option in diagnosis of FAs. Regular screening may be advisable in patients with FAs and a family history of breast cancer in a first-degree relative. More rigorous research is needed in this area.

Constructing "sound science" and "good epidemiology": tobacco, lawyers, and public relations firms

The tobacco industry has attacked "junk science" to discredit the evidence that secondhand smoke-among other environmental toxins-causes disease. Philip Morris used public relations firms and lawyers to develop a "sound science" program in the United States and Europe that involved recruiting other industries and issues to obscure the tobacco industry's role. The European "sound science" plans included a version of "good epidemiological practices" that would make it impossible to conclude that secondhand smoke-and thus other environmental toxins-caused diseases. Public health professionals need to be aware that the "sound science" movement is not an indigenous effort from within the profession to improve the quality of scientific discourse, but reflects sophisticated public relations campaigns controlled by industry executives and lawyers whose aim is to manipulate the standards of scientific proof to serve the corporate interests of their clients.