Confounding and bias in observational studies in inflammatory bowel disease: a meta-epidemiological study.

BACKGROUND: Observational research concerning inflammatory bowel disease (IBD) is highly susceptible to spurious findings because of confounding and bias. AIM: To investigate how these issues were reported in this research field. METHODS: We identified and appraised a random sample of 160 observational studies concerning IBD published in high-impact gastroenterology journals and the most respected specialty journals of the condition. We applied a standardised methodology to assess how confounding and bias were reported and discussed, and investigated the association between yearly citations and study characteristics using mixed-effect multivariable regression analysis. RESULTS: The authors of 67 out of 160 articles (41.9%) mentioned confounding, and in 89 cases (55.6%) reported any bias. Although most authors applied strategies to minimise confounding or bias (n = 139; 86.9%) and acknowledged at least one unadjusted confounder (n = 116; 72.5%), a minority commented about whether the main findings could have been affected (n = 60; 37.5%). Very few authors (n = 7; 4.4%) called for caution in interpreting the results in the discussion. Reporting of confounding and bias was particularly lacking for case-control studies, those not using routinely collected data, those employing laboratory analyses as the primary method of assessment and studies investigating non-modifiable exposures. In adjusted analyses, mentioning or alluding to confounding was positively associated with yearly citations (P = 0.010), whereas calling for a cautious interpretation of the findings was not. CONCLUSIONS: Reporting of confounding is inadequate and its acknowledgement is often neglected in interpreting high-impact observational research in IBD. These results encourage a more careful evaluation of the consequences of confounding and bias.