Correction of Survival Bias in a Study About Increased Mortality of Heads of Government
A recent study reported increased mortality of heads in government. To avoid the time-dependent bias (also known as immortal-time bias), survival from last election was compared between election winners and runners-up. We claim that this data manipulation results in bias due to conditioning on future events; survival should be compared from first election as well as winning should be considered as a time-dependent covariate. We collected the missing life-time periods and redesigned the study to display this bias using Lexis diagrams and multistate methodology. We found that the bias that we termed the healthy candidate bias was even more severe than the time-dependent bias.