The association between mortality, morbidity and age in New Zealand's oldest old.

People aged eighty-five years and over (the oldest old) will form an increasing proportion of the population of New Zealand and many other countries. Because of their smaller numbers and relative inaccessibility, their health status has sometimes been extrapolated from populations of people aged sixty-five to eighty-four years. For people aged sixty-five to eighty-four years an exponential relationship is seen between age and morbidity and mortality. We explore if this exponential relationship extends to people aged ninety years and over. We analyzed data from the New Zealand 1991 Census and 1992 hospital discharge records and, for people aged sixty to eighty-nine years, confirmed an exponential relationship between age and mortality, inactivity, hospital utilization, and occupation of residential institutions. This exponential trend did not continue for people aged ninety years and over for whom mortality rates and indicators of morbidity were considerably lower than expected, and conclude that the actual health status of people aged ninety years and over is better than the status extrapolated from that of people aged sixty to eighty-nine years.