Consistency of causal claims in observational studies: a review of papers published in a general medical journal

ObjectiveTo evaluate the consistency of causal statements in observational studies published in The BMJ.DesignReview of observational studies published in a general medical journal.Data sourceCohort and other longitudinal studies describing an exposure-outcome relationship published in The BMJ in 2018. We also had access to the submitted papers and reviewer reports.Main outcome measuresProportion of published research papers with ‘inconsistent’ use of causal language. Papers where language was consistently causal or non-causal were classified as ‘consistently causal’ or ‘consistently not causal’, respectively. For the ‘inconsistent’ papers, we then compared the published and submitted version.ResultsOf 151 published research papers, 60 described eligible studies. Of these 60, we classified the causal language used as ‘consistently causal’ (48%), ‘inconsistent’ (20%) and ‘consistently not causal’(32%). Eleven out of 12 (92%) of the ‘inconsistent’ papers were already inconsistent on submission. The inconsistencies found in both submitted and published versions were mainly due to mismatches between objectives and conclusions. One section might be carefully phrased in terms of association while the other presented causal language. When identifying only an association, some authors jumped to recommending acting on the findings as if motivated by the evidence presented.ConclusionFurther guidance is necessary for authors on what constitutes a causal statement and how to justify or discuss assumptions involved. Based on screening these papers, we provide a list of expressions beyond the obvious ‘cause’ word which may inspire a useful more comprehensive compendium on causal language.

The impact factor: a case study of medical journals

Purpose – This paper aims to look at two well-respected cardiothoracic journals and one general medical journal over the period of a decade to find out any major differences in content and referencing to warrant the fact that the general journal should be ranked far higher than the specialist journals. Design/methodology/approach – The paper conducted citation analysis and comparison with impact factors (IFs) of two cardiothoracic journals, one American and one European, and one general medical journal over the period. Findings – The study concludes that although there was a significant amount of self-referenced non-citable material in the general medical journal, this probably did not alone account for its higher ranking. Research limitations/implications – The original articles were actually very highly cited, and perhaps, the visibility of the general medical journal could possibly be the main factor contributing to its high IF. Practical implications – In terms of citation, all contribution in an issue of a journal is not equal, and therefore, to evaluate work by looking at the IF of the journal in which it is published is not reliable. Originality/value – The study is based on an original citation and IF analysis, and the results should be of interest and value to all those concerned with the use of the IF to evaluate journals.