Rectangularization of the survival curve: implications of an ill-posed question.

There has been considerable interest in the question of whether the human survival curve is becoming more rectangular as life expectancy in developed countries increases. However, despite the intuitive appeal of the rectangularization concept it has not been translated into a formally stated hypothesis about the shape of the human survival curve. This article examines how the hypothesis of rectangularization can be formally stated and the implications of that formalization for research on health and functional changes at later ages.