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Projections of Education Statistics to 2018

NCES 2009-062
September 2009

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 200506. 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 affected by changes in graduation requirements, but this is not considered in the projections in this report.

Projections of private high school graduates were calculated using the same methodology as public high school graduates, using data from biennial NCES Private School Universe Survey (PSS) from 198889 to 200506. Since the PSS is collected in the fall of odd numbered years, data for even numbered years without a PSS collection were estimated using data from the PSS.

Projection Accuracy

An analysis of projections from models used in the past 18 editions of Projections of Education Statistics indicates that the mean absolute percentage errors (MAPEs) for projections of public high school graduates were 1.0 percent for 1 year ahead, 0.9 percent for 2 years ahead, 1.8 percent for 5 years ahead, and 3.8 percent for 10 years ahead. For the 1–year–ahead prediction, this means that one would expect the projection to be within 1.0 percent of the actual value, on the average. For more information on the mean absolute percentage errors, see table A–2.

State Level

This edition contains projections of high school graduates from public schools by state from 200607 to 201819. Public school graduate data from the Common Core of Data survey for 198081 to 200506 were used to develop these projections. This survey does not collect graduate data for private schools at the state level.

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 200506. 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 jurisdictions were projected using the same single exponential smoothing parameter of 0.4. Projections of grade 12 enrollment were developed based on the grade progression rates discussed in appendix A, Enrollment. The projected rates were 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.

Adjustment to National Projections

The projections of state high school graduates were adjusted to sum to the national projections of public high school projections shown in table 24. This was done through the use of ratio adjustments in which all the states' high school graduate projections were multiplied by the ratio of the national high school graduate projection to the sum of the state high school projections.

Regional Projections

For each region, the projections of high school graduates equaled the sum of the high school projections of the states within the region.

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