Quantification of health status changes in China and Canada: an evaluation of a stochastic model of aging

How can we characterize the health of a whole population? One way is through the chance of dying, or the mortality rate. Death is a highly personal event, but the mortality rate is a public health measure, and applies to people 'on average'. Even so, what makes up 'average health status' is not always easy to say, and generally must be adjusted by age. But for individuals, being alive is just the start; it is also useful to know the chances of being alive and well, or alive and ill. Another way to think about problem of how to relate mortality risk to individual health status is to think again about age. An individual's age can be measured in two ways - the time since birth, which can be known with precision, and the time until death, which is not knowable for an individual. As it turns out, however, it is possible to know with some precision an individual's chance of dying, when the health status of that person is known, and compared with the experience of other people with the same health status - in essence to the number of things they have wrong with them. So while we cannot tell exactly when a person might die, we can indicate on, average, how long they are likely to live. Our group has also shown that we can estimate the chance of a person's health staying the same, or getting better, or worsening. This too is related precisely to the number of things that they have wrong with them. Intriguingly, the number of things that people have wrong with them appears to be fairly easy to measure. Some people appear to have nothing wrong with them, so it could be that their chance of dying (or having worse health) is a reflection of the ambient or background or population risk of dying or having worse health. If so, the outcomes of what happens when people have nothing wrong with them might serve as a public health measure. This might be especially useful for older people, and is the focus of this study.