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

Abstract

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.

Figure 1

Distribution of P values for first primary result in each article and corresponding absolute values of standardised normal deviates z (two sided P=0.05, 0.01, 0.001, and 0.0001 correspond to z=1.96, 2.58, 3.29, and 3.89, respectively)