Objectives: Poor quality of reporting of confounding has been observed in observational studies prior the STrenghtening the Reporting of Observational studies in Epidemiology (STROBE) statement, a reporting guideline for observational studies. We assessed whether the reporting of confounding improved after the STROBE statement.

Study Design and Setting: We searched MEDLINE for all articles about observational cohort and case control studies on interventions with a hypothesized beneficial effect in five general medical and five epidemiologic journals published between January 2010 and December 2012. We abstracted data for the baseline period before the publication of the STROBE statement (January 2004 April 2007) from a prior study. Six relevant items related to confounding were scored for each article. A comparison of the median number of items reported in both periods was made.

Results: In total, 174 articles published before and 220 articles published after the STROBE statement were included. The median number reported items was similar before and after the publication of the STROBE statement [median, 4; interquartile range [IQR], 3-5 vs. median, 4; IQR, 3.75-5]. However, the distribution of the number of reported items shifted somewhat to the right (P = 0.01).

Conclusion: Although the quality of reporting of confounding improved in certain aspects, the overall quality remains suboptimal. (C) 2016 Elsevier Inc. All rights reserved.