A format was devised with generic categories for estimates of the number of cases, complications, sequelae, and deaths associated with each disease. Three levels of severity were established for both acute and chronic morbidity and provision was made for recording the duration of an acute illness. The scheme also was designed to allow distribution of cases, complications, sequelae, and deaths among six age groups. An example of the matrix used to compile these estimates is shown in Table 4.1; the methods used to determine the entries are described below. Data on individual diseases are presented in Appendixes C through P.
Individual value judgments (trade-off values)* on the disutility of particular disease states were elicited through a questionnaire (see Appendix Q) completed by individual committee members. Respondents to the questionnaire were first asked to judge the undesirability of one unit of each acute and chronic morbidity category against death within a specific age group. The units were specified as one day for each state of acute illness and one case for each type of chronic illness (assumed to last a lifetime). Respondents then were asked to evaluate the undesirability of deaths across age groups. An example is shown in Table 4.2. The morbidity/mortality and age categories used in the questionnaire were those described above. The scheme was designed to cover all major conditions that result from infectious diseases.
With these trade-offs, a set of values was derived for each respondent that represented on a single numeric scale the individual’s feelings about various disease consequences. The unit of comparison was designated as the “infant mortality equivalence” (IME) value. The IME value of a morbidity category/age group combination was calculated by multiplying the trade-off value for that combination by the trade-off value assigned to a death in that age group compared to the death of an infant under one year of age (for an example derived from Table 4.2, see Table 4.3).
Specific infant mortality equivalence values can be combined with disease burden estimates such as those given in Appendixes C through P to generate scores that express the seriousness of a disease relative to others as viewed by the individual making the trade-off decisions.