There are different ways to measure the timing of an event. In example 1 (marital status and mortality) the outcome variable was calendar time since the baseline survey. An alternative is to analyse age at death (time since birth). Since the subjects were interviewed at different ages, the "entry age" would differ. In theory using age as the time scale (with different entry age) is often preferred in such an epidemiological study, but the actual advantage depends on situations. See Korn et al. Time-to-event analysis of longitudinal follow-up of a survey. Am J Epidemiol 1997; 145: 72-80; and their commentators Ingram et al. Am J Epidemiol 1997; 146: 528-529.