Measuring achievement: changes in risk factors for cardiovascular disease in Australia.

A possible measure for evaluating health system performance is the achievement index, which can be calculated using prevalence and distribution of a health measure across different socioeconomic groups. This study extends this approach by examining how achievement can be represented on a two-dimensional plane with the x-axis being the difference in mean ill-health and the y-axis being the difference in an absolute measure of inequality based on the generalised concentration index. The achievement plane is an easily understandable visual aid which provides a method of tracking changes in health and inequality over time, as well as uncertainty around these measures. We also demonstrate how comparisons over time and at different levels of inequality aversion can be undertaken using measures of net achievement. To illustrate the use of the achievement plane, we compared changes in prevalence of various cardiovascular risk factors and absolute inequality in the distribution of these factors, using data from four successive Australian National Health Surveys conducted between 1989 and 2005. While self-reported rates of smoking and high cholesterol have been declining, inequalities have been rising as the greatest reductions in these risk factors have been among higher income groups. Conversely for risk factors where the prevalence has been increasing, health inequalities are either not changing (i.e. diabetes and obesity), or diminishing over time (overweight/obese). All of these changes can be summarized using an achievement plane and graphs of net achievement to examine changes in prevalence and distribution of these risk factors over time.