Over time, the spread of ages over which individuals die (on average) has narrowed. In other words, mortality has been compressed into a shorter period: a particular cohort of individuals might expect to die within a 10 year period (on average) now rather than over a longer period. The compression of mortality effect is largely a result of the reduction of premature deaths. The effect of compression of mortality is to make the survival curve more rectangular (rather than triangular) in shape: the probability of survival remains high until a particular age, and then tails off sharply in this compressed mortality period.