Biases

Confirmation bias

The search for and use of information to support an individual’s ideas, beliefs or hypotheses.

Confounding

A distortion that modifies an association between an exposure and an outcome because a factor is independently associated with the exposure and the outcome.

Confounding by indication

A distortion that modifies an association between an exposure and an outcome, caused by the presence of an indication for the exposure that is the true cause of the outcome.

Data-dredging bias

A distortion that arises from presenting the results of unplanned statistical tests as if they were a fully prespecified course of analyses.

Detection bias

Systematic differences between groups in how outcomes are determined.

Diagnostic access bias

Individuals differ in their geographic, temporal and economic access to diagnostic procedures which label them as having a given disease.

Diagnostic suspicion bias

Knowledge of a subject’s prior exposures or personal biases may influence both the process and the outcome of diagnostic tests.

Differential Reference bias

When not all participants receive the same reference test in a diagnostic accuracy study.

Early Stopping Bias

A distortion of treatment effect estimates that arises when a clinical trial is stopped early, whether for benefit, futility, or safety, following an interim analysis.

A distortion in a recorded measurement caused by human tendencies to round to specific end-digits, usually zero or five, or to a reading just below or above a threshold where treatment or another action is required.

Hawthorne effect

When individuals modify an aspect of their behaviour in response to their awareness of being observed.

Healthy User bias

Occurs when people who use an intervention are inherently healthier, more health-conscious, or more engaged with healthcare than non-users, leading to an apparent effect that is partly or wholly attributable to these underlying differences rather than to the intervention itself.

Hot stuff bias

When a topic is fashionable (‘hot’) investigators may be less critical in their approach to their research, and investigators and editors may not be able to resist the temptation to publish the results.

Hypothetical bias

A distortion that arises when an individual’s stated behaviour or valuation differs to that of their real behaviour or valuation.

Immortal time bias

A distortion that modifies an association between an exposure and an outcome, caused when a cohort study is designed so that follow-up includes a period of time where participants in the exposed group cannot experience the outcome and are essentially ‘immortal’.

Catalogue of Bias

Confirmation bias

Confounding

Confounding by indication

Data-dredging bias

Detection bias

Diagnostic access bias

Diagnostic suspicion bias

Differential Reference bias

Early Stopping Bias

End-digit preference bias

Hawthorne effect

Healthy User bias

Hot stuff bias

Hypothetical bias

Immortal time bias