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Projections of Education Statistics to 2014, published September 2005.

Appendix A. Projection Methodology: High School Graduates

National

Projections of public high school graduates were developed in the following manner. The number of public high school graduates was expressed as a percent of grade 12 enrollment in public schools for 197273 to 200102. This percent was projected using single exponential smoothing and applied to projections of grade 12 enrollment to yield projections of high school graduates in public schools. (This percent does not make any specific assumptions regarding the dropout rate. The effect of the 12th- grade dropout proportion is reflected implicitly in the graduate proportion.) The grade 12 enrollment was projected based on grade progression rates. This percent was assumed to remain constant at levels consistent with the most recent rates. This method assumes that past trends in factors affecting graduation ratios, such as dropouts, migration, and public or private transfers, will continue over the projection period. In addition to student behaviors, the projected number of graduates could be impacted by changes in policies affecting graduation requirements.

Projections of private high school graduates were calculated using the same methodology as public high school graduates, using data from 198889 to 200002.

Projection Accuracy

An analysis of projections from models used in the past 14 editions of Projections of Education Statistics indicates that the mean absolute percentage errors (MAPEs) for projections of public high school graduates were 0.8 percent for 1 year ahead, 0.9 percent for 2 years ahead, 1.2 percent for 5 years ahead, and 4.2 percent for 10 years ahead. For the 1-year ahead prediction, this means that one would expect the projection to be within 0.8 percent of the actual value, on the average. For more information on the mean absolute percentage errors, see table A2.

State Level

This edition contains projections of high school graduates from public schools by state from 200203 to 201314. Public school graduate data from the National Center for Education Statistics Common Core of Data survey for 198081 to 200102 were used to develop these projections. This survey does not collect graduate data for private schools.

Projections of public high school graduates by state were developed in the following manner. For each state, the number of public high school graduates was expressed as a percent of grade 12 enrollment in public schools for 198081 to 200102. This percent was projected using single exponential smoothing and applied to projections of grade 12 enrollment to yield projections of high school graduates in public schools. All states, with the exception of Washington, DC, were projected using the same single exponential smoothing parameter. Due to the quality of the Washington, DC data, the smoothing parameters for Washington DC were estimated using a feature of the model software program EViews 4.1 using the available historical data. This approach yielded more consistent projections of Washington, DC graduates. Projections of grade 12 enrollment were developed based on the grade progression rates discussed in appendix A, Enrollment. This percent was assumed to remain constant at levels consistent with the most recent rates. This method assumes that past trends in factors affecting public high school graduates will continue over the projection period.

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