The purpose of this study was, first, to examine and critique the more popular incidence sources for handicapping conditions in the school age population, and second, to establish reasonably reliable base line data on which the future analysis of special population groups can be grounded. On the basis of this study, we suggest that the National Center of Health Statistics estimates become the primary source for further analysis due to both their reliability and comparability. It is questionable whether these figures could be refined further by conducting an independent national survey of school children. Data reliability is important, since even very small errors in estimating the number of children to be served can have significant financial implications. For example, on the basis of individual state estimates of the excess costs of serving handicapped children, the average state expenditure is $726 per child. Since no state spends less than $400, this figure can be used as illustrative of minimal changes in costs for given errors in estimation. Thus, assuming an excess cost formula and a minimum reimbursement of $400 per child, a one-tenth of one percent error would cost approximately $18 million. Another important aspect of this report is that it focuses on age group differences in the handicapped population. The use of aggregate estimates across age groups and grade levels has been somewhat misleading in the past. This is because there are significant differences in the age distribution of certain handicapping conditions, at least in terms of their impact upon the ability of a child to benefit from regular education. As suggested in this report, there is a significant drop in reported incidence at the age that typically corresponds to the transition period between elementary and secondary school. It is also interesting that the greatest differences in identification patterns between BEH and NCHS occur at the elementary level. The only difference at the secondary level is in the identification of the emotionally disturbed. The striking difference in distribution in age and grade levels in some handicapped classifications clearly identifies the need for federal consideration of these factors in developing a strategy for targeting of funds.
Patricia Craig and Norman McEachron. "The Development and Analysis of Base Line Data for the Estimation of Incidence in the Handicapped School Age Population" SRI International (1975).