[Immortal time bias in pharmacoepidemiological studies: definition, solutions and examples]

Therapie. 2015 May-Jun;70(3):259-63. doi: 10.2515/therapie/2014207. Epub 2014 Dec 10.
[Article in French]


Among the observational studies of drug effects in chronic diseases, many of them have found effects that were exaggerated or wrong. Among bias responsible for these errors, the immortal time bias, concerning the definition of exposure and exposure periods, is relevantly important as it usually tends to wrongly attribute a significant benefit to the study drug (or exaggerate a real benefit). In this article, we define the mechanism of immortal time bias, we present possible solutions and illustrate its consequences through examples of pharmacoepidemiological studies of drug effects.

MeSH terms

  • Bias*
  • Chronic Disease
  • Humans
  • Pharmaceutical Preparations / administration & dosage
  • Pharmacoepidemiology / methods*
  • Research Design*
  • Time Factors


  • Pharmaceutical Preparations