Design of a landmark analysis to prevent immortal time bias. In the landmark analysis, follow-up starts at a chosen time period after a certain event, in this example at 6 months. Hence all individuals that died before Month 6 are excluded from the analysis (Individual 4). Individuals are then classified according to exposure status in the first 6 months. Individuals 3, 5 and 6 are therefore considered treated, whereas Individuals 1 and 2 are considered untreated.