Factors affecting the projections
The projections of current expenditures are related to projections of economic growth as measured by disposable income per capita and assistance by state governments to local governments. For more details, see appendixes A.0 and A.4.
Factors that were not considered
Many factors that may affect future school expenditures were not considered in the production of these projections. Such factors include policy initiatives as well as potential changes in the age distribution of elementary and secondary teachers as older teachers retire and are replaced by younger teachers, or as older teachers put off retirement for various reasons.
About constant dollars and current dollars
Throughout this section, projections of current expenditures are presented in constant 2010-11 dollars. The reference tables, later in this report, present these data both in constant 2010-11 dollars and in current dollars. The projections were developed in constant dollars and then placed in current dollars using projections for the Consumer Price Index (CPI) (table B-6 in appendix B). Projections of current expenditures in current dollars are not shown after 2014-15 due to the uncertain behavior of inflation over time.
An analysis of projection errors from similar models used in the past 21 editions of Projections of Education Statistics that contained expenditure projections indicates that mean absolute percentage errors (MAPEs) for total current expenditures in constant dollars were 1.3 percent for 1 year out, 2.1 percent for 2 years out, 2.6 percent for 5 years out, and 4.0 percent for 10 years out. For the 1-year-out prediction, this means that one would expect the projection to be within 1.3 percent of the actual value, on average. MAPEs for current expenditures per pupil in fall enrollment in constant dollars were 1.3 percent for 1 year out, 2.1 percent for 2 years out, 2.9 percent for 5 years out, and 5.2 percent for 10 years out. See appendix A for further discussion of the accuracy of recent projections of current expenditures, and see table A-2 in appendix A for the mean absolute percentage errors (MAPEs) of these projections.