Attrition in geriatric research: how important is it and how should it be dealt with?

Attrition, defined as a total loss to follow-up of participants, is a potential major bias in clinical trials. Participants can be lost for many reasons (death, illness, worsened health, refusal, withdrawal, lost to follow up). Attrition may be higher in older populations, so geriatric researchers should pay particular attention to the difficulties it raises. For a proper interpretation of research findings, a detailed analysis of the type of attrition observed and its possible determinants is essential, to determine if attrition has occurred at random or if it is associated to certain patient or treatment characteristics. This paper aims to review different causes of attrition, its prevalence among studies in different elderly populations, and its consequences on research findings. In addition, strategies used to minimise attrition (tracking, bonding, incentives) are discussed, and methods proposed to take this phenomenon into account are proposed.