page 19 Unlike the estimate of need in column (7) of Table 3, the Michigan study explicitly incorporates assumptions on the proportion of cases in each age group for each disease that wil seek treatment from the VHW (Grosse et l. Appendix B). These proportions range from .90 for severe diarrhea and upper respiratory infection down to .30 for intestinal parasites and .10 for complicatdons of childbirth and pregancy. While some of these fLgures seem rather high, the face that these adjustments have been made makes the Javanese estimate more comparable to the Ghanaian estimate based on "demand" than to that based on "need." Thus the Javanese estimate is twice as large as the comparable one for Ghana.

An examination of the the details of the Michigan study calculations reveal that they were more optimisitic than were the Ghanaian analysts regarding the productivity of the VH W. The Michigan analysts assumed the VUW vould have some effect on mortality or morbidity for 20 of the 31 diseases analyzed, whereas the Ghanaian analysts hoped for such an impact on only nine diseases. Furthermore, for those problems which both studies assumed the VHW would influence, the Michigan study assumed a greater VhW effectiveness. Column (6) of Table 5 presents the implied effectiveness of the VHW in the Michigan study which compares most directly with each of **the** values from column (3) of Table 3. Setting aside colds and skin infections as not having been considered by Ghanaian analysts (and in any event of trivial consequence for total LDS), the column (6) effectiveness fliure for Java **is** typically greater than the corresponding Ghanaian figure. These greater effectiveness estimates, together with the larger number of diseases the Javanese VHW is assumed to influence and the higher level of assumed demand combine to make the estimate of 15 LDS per encounter a relatively optimistic one. Nevertheless, it is encouraging that it is of the same order of magnitude as the estimate for Ghana.

3. Estimates of Parameters of the Cost Functions. Turning now to the dight-hand-sLde of decision rule (9), consider the parameter Ilf This parameter was defined in section m above as the ratio of two numbers. The denominator of this ratio is the number of vaccinations that a fixed center operating on budget C* could deliver on site in one year, if it has no responsibility for VHW support and supervision. (In section ml, this number was called V*.) The numerator is the number oZ encounters that the same fixed center could support on the same budget through the supervision of outlying VHWs. To determine this number with any confidence will require detailed cost and management studies of fixed centers with outreach and VH W supervision activities in several developing countries.

However suppose that the cost (net of vaccine costs) of traveling to within reach of Q people is directly proportional to Q to the power s, where s is the degree of returns to scale in the cost function (and bears the same interpretation as the returns to scale parameter introduced in equation (2) of section **I).** Suppose the cost function is roughly the same whether the purpose of travel is to vaccinate the target group within Q by a mobile team or to supervise the VHWs aho serve Q by a fixed center, provided that only one of these two tasks is performed. Under these assumptions, Table 6 develops an estimate of Pf for each of several values of s based on preliminary estimates of the costs of a mobile vaccination team operating in Abengourou, Ivory Coast, in 1981 (Sanoh, 1983). (16]