บท 342: The Moral Imperative Towards Cost-Effectiveness[2]
There are a number of complications and choices regarding the calculation of DALYs, which given rise to a number of subtly different versions of DALYs and the closely related units called QALYs. Chief among these is the question of the size of the weightings representing how bad it is on average to suffer from a particular disability. There are also considerations about discount rates and age weightings.
Different reasonable choices on these parameters could change the number of DALYs due to a condition by a few percent or by as much as a factor of two. DALYs should thus be considered only as a rough measure of the disvalue of different conditions. It might seem that there would be little use for so rough a measure. This would be true if the difference in cost-effectiveness between interventions were also about a factor of two, but since it is often a factor of a hundred or more, a rough measure is perfectly adequate for making the key comparisons.
Let us now address all of the three concerns, by looking at a real world example of funding the prevention or treatment of HIV and AIDS. Let us consider four intervention types: surgical treatment for Kaposi's sarcoma (an AIDS defining illness), antiretroviral therapy to fight the virus in infected people, prevention of transmission of HIV from mother to child during pregnancy, condom distribution to prevent transmission more generally, and education for high risk groups such as sex workers. It is initially very unclear which of these interventions would be best to fund, and one might assume that they are roughly equal in importance. However, the most comprehensive compendium on cost-effectiveness in global health, Disease Control Priorities in Developing Countries 2nd edition (hereafter DCP2), lists their estimated cost-effectiveness as follows:[3]
Note the wide discrepancies between the effectiveness of each intervention type. Treatment for Kaposi's sarcoma cannot be seen on the chart at this scale, but that says more about the other interventions being good than about this treatment being bad: treating Kaposi's sarcoma is considered cost-effective in a rich country setting. Antiretroviral therapy is estimated to be 50 times as effective as treatment of Kaposi's sarcoma; prevention of transmission during pregnancy is 5 times as effective as this; condom distribution is about twice as effective as that; and education for high risk groups is about twice as effective again. In total, the best of these interventions is estimated to be 1,400 times as cost-effectiveness as the least good, or more than 1,400 times better than it would need to be in order to be funded in rich countries.
This discrepancy becomes even larger if we make comparisons between interventions targeted at different types of illness. DCP2 includes cost-effectiveness estimates for 108 health interventions, which are presented in the chart below, arranged from least effective to most effective.[4]
This larger sample of interventions is even more disparate in terms of costeffectiveness. The least effective intervention analysed is still the treatment for Kaposi's sarcoma, but there are also interventions up to ten times more cost-effective than education for high risk groups. In total, the interventions are spread over more than four orders of magnitude, ranging from 0.02 to 300 DALYs per $1,000, with a median of 5. Thus, moving money from the least effective intervention to the most effective would produce about 15,000 times the benefit, and even moving it from the median intervention to the most effective would produce about 60 times the benefit.
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