Cost-Effectiveness and Population Impact
An intervention CER, whether average or incremental, is based on assumptions about introduction, expansion, contraction, or modification of the activity compared with current (or sometimes "best") practice. Comparison of ratios indicates whether one intervention offers better or worse value for money than another at the individual level but says nothing about how either one affects the whole population. The analysis, therefore, includes, wherever possible, two ways of describing the latter effect. One is to consider a population of 1 million, with a typical regional age and sex structure, and to suppose that the intervention were delivered to all the potential beneficiaries. That number of people is just the prevalence or incidence of the condition times 1 million. The total cost would then be the unit cost times that number (or the cost of reaching that many people if the unit cost varies with coverage). The total health gain would be the individual effectiveness times that same number (or the overall outcome if that depends on externalities, such as the transmission of communicable disease, that are sensitive to coverage). Standardizing on a population of 1 million allows comparisons among regions and interventions in which the incidence or prevalence may vary greatly.
A second approach standardizes not on population but on expenditure: if an additional US$1 million were devoted to the resources needed for an intervention, how many people could benefit from it and how large would the health gain be? The coverage of the intervention would be US$1 million divided by the average cost, and the total gain in DALYs would be that number of people times the average effectiveness. This approach is applied in relatively few chapters because of the information requirements; its advantage is to facilitate judgments as to where increased spending would be most justified—where it would yield the largest improvement in health, reach the most people, or account for the largest share of burden from a condition. Table 1.3 in chapter 1 provides examples for some interventions to reduce child mortality, prevent or treat HIV and AIDS, reduce smoking prevalence, treat heart attack and stroke, detect and treat cervical cancer, and operate a basic surgical ward. The estimates of DALYs gained per US$1 million vary from less than 100 to more than 100,000—a thousandfold difference in value for money. Annex 26.A of chapter 26 provides both kinds of calculations, per million population, to compare the cost-effectiveness of interventions for improved maternal health in South Asia and Sub-Saharan Africa.
