Correction of survival bias in a study about increased mortality of heads of government

<p>A recent study reported increased mortality of heads in government. To avoid the time-dependent bias (also known as immortal-time bias), survival from <i>last</i> 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 <i>first</i> election as well as winning should be considered as a time-dependent covariate. We collected the missing life-time periods and re-designed the study to display this bias using Lexis diagrams and multi-state methodology. We found that the bias that we termed the healthy candidate bias was even more severe than the time-dependent bias.</p>