Use of an epidemiological model for estimating the effectiveness of tuberculosis control measures. Sensitivity of the effectiveness of tuberculosis control measures to the social time preference.

Different combinations of coverage levels of BCG vaccination and of case-finding and treatment may achieve the same problem reduction in epidemiological terms. But the same problem reduction, in man-years of tuberculosis, may be valued differently in social terms.A social-time-preference parameter, of the form 1/(1+r)(t), is relevant to this evaluation and the level of r is critical for policy decision. The present paper studies the sensitivity of the effectiveness of BCG vaccination and of case-finding and treatment to the level of r, and the epidemiological mechanism underlying such sensitivity. A high value of r can be visualized as corresponding to a close planning horizon, a lower value of r to a more distant one. At any level of epidemiological effectiveness, a planner with a high value of r would favour case-finding and treatment, and a planner with a low value of r would tend to emphasize BCG vaccination. This influence of the social-time-preference parameter on the planner's decision is found to depend on the discounting effect of the parameter on the one hand, and on the different age- and time-patterns of the preventive effect of the major control measures, on the other.