The hazard ratio as a measure of effect in clinical trials of elderly populations: common pitfalls and misconceptions.

The hazard ratio is a measure of effect which is of paramount importance in etiological research, that is in studies aimed at assessing the strength of the causal relationship between a given treatment/exposure and a certain outcome. Despite the widespread use of the hazard ratio as a measure of effect in scientific reports and articles, the interpretation of this index is often accompanied by some misconceptions which can jeopardize the critical appraisal of randomized clinical trials (RCTs) and observational studies as well. Herein, using a series of examples derived from RCTs in the elderly subjects, we address major pitfalls regarding the interpretation of the hazard ratio in geriatric research.