ABSTRACT
In a clinical trial of a certain medicine, time zero is when patients • are randomly allocated to treatments. Time to event is the time till cancer remission or time till a clinical indicator falls below a certain level, for example, viral count falls below 500. In an epidemiological study the event of interest could be the wean-• ing of newborn baby. Time zero is the birth of the child, and time to the event is the last day the baby breastfeeds. Another epidemiological study could meas ure the time from when • a person starts consuming intravenous drugs until infection with the HIV virus. In industrial durability tests it is of interest to know, for example, • how long a car tire lasts. In this case, instead of time to event, kilometers to event is used. That is, instead of recording the time the tire is on the road, the distance in kilometers run by the car till the tire wears out is recorded. In a psychological study it is of interest to know, for example, the • time it takes 2-year old children to learn a certain task. In a sociological study the event of interest could be returning to jail • after having left jail for the first time. That is, the time to event would be measured from when the person was let out of jail for the first time till the person returns due to a new offence. In a SSL, time to event would be measured from when the prod-• uct left the manufacturing plant till it was rejected by a consumer (Hough et al. 2003).
