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Trends in High School Dropout and Completion Rates in the United States: 1972–2008

NCES 2011-012
December 2010

Defining and Calculating Dropout and Completion Rates Using the CPS

Event Dropout Rates

The October Supplement to the CPS is the only national data source that currently can be used to estimate annual national dropout rates. As a measure of recent dropout experiences, the event dropout rate measures the proportion of students who dropped out over a 1-year interval.

The numerator of the event dropout rate for 2008 is the number of persons ages 15–244 surveyed in October 2008 who were enrolled in grades 10–12 in October 2007, who were not enrolled in high school in October 2008, and who also did not complete high school (that is, had not received a high school diploma or an alternative credential such as an equivalency certificate) between October 2007 and October 2008.

The denominator of the event dropout rate for 2008 is the sum of the dropouts (that is, the numerator) and all persons ages 15–24 who were attending grades 10–12 in October 2007, who were still enrolled in October 2008, or who graduated or completed high school between October 2007 and October 2008.

The dropout interval is defined to include the previous summer (in this case, the summer of 2008) and the previous school year (in this case, the 2007 school year), so that once a grade is completed, the student is then at risk of dropping out of the next grade. Given that the data collection is tied to each person’s enrollment status in October of 2 consecutive years, any student who drops out and returns within the 12-month period is not counted as a dropout.

Status Dropout Rates

The status dropout rate reflects the percentage of individuals who are dropouts, regardless of when they dropped out. The numerator of the status dropout rate for 2008 is the number of individuals ages 16–245 who, as of October 2008, had not completed high school and were not currently enrolled. The denominator is the total number of 16- through 24-year-olds in October 2008.

Status Completion Rates

The numerator of the high school status completion rate is the number of 18- through 24-year-olds6 who had received a high school diploma or an alternative credential such as a GED. The denominator is the number of 18- through 24-year-olds who are no longer in elementary or secondary school.

GED Credentials and the Status Completion Rate. Prior to 2000, editions of this series of high school completion and dropout reports presented estimates of overall status completion rates and estimates of the method of completion—graduation by diploma or completion through an alternative credential such as the GED—based on data obtained through CPS reporting. Because of changes in CPS introduced in 2000, data on the method of completion were not comparable with prior year CPS estimates and the method of completion data were no longer reported. Please see the discussion of the GED Testing Service data below for further information.

Data Considerations for the CPS

Over the last several decades, data collection procedures, items, and data preparation processes have changed in the CPS. Some of these changes were introduced to ensure that CPS estimates were comparable to those from decennial Census collections, some were introduced to reflect changes in the concepts under study, some were introduced to improve upon measures, and some were introduced to develop measures for new phenomena. The effects of the various changes have been studied to help ensure they do not disrupt trend data from the CPS. For a summary of the changes and studies of their effects, please see appendix C of Dropout Rates in the United States: 2001 (Kaufman, Alt, and Chapman 2004).

CPS data include weights to help make estimates from the data representative of the civilian, noninstitutionalized population in the United States. These weights are based on decennial Census data that are adjusted for births, deaths, immigration, emigration, etc., over time.

Imputation for Item Nonresponse in the CPS. For many key items in the October CPS, the U.S. Census Bureau imputes data for cases with missing data due to item nonresponse. However, the U.S. Census Bureau did not impute data regarding the method of high school completion before 1997. Special imputations were conducted for these items using a sequential hot deck procedure implemented through the PROC IMPUTE computer program developed by the American Institutes for Research. Three categories of age, two categories of race, two categories of sex, and two categories of citizenship were used as imputation cells.

Age and Grade Ranges in CPS Estimates. The age and grade ranges used in the CPS measures of dropout rates are constrained by available data. Ideally, the estimates would be able to capture reliable estimates of children in grades as low as grade 9. However, the CPS asks the question about enrollment in the previous October only about individuals ages 15 and older. Many 9th-graders are younger than age 15, so 10th grade was selected as the lower boundary of grade ranges in the event dropout rate.

Accuracy of CPS Estimates. CPS estimates in this report are derived from samples and are subject to two broad classes of error—sampling and nonsampling error. Sampling errors occur because the data are collected from a sample of a population rather than from the entire population. Estimates based on a sample will differ to some degree (dependent largely on sample size and coverage) from the values that would have been obtained from a universe survey using the same instruments, instructions, and procedures. Nonsampling errors come from a variety of sources and affect all types of surveys—universe as well as sample surveys. Examples of sources of nonsampling error include design, reporting, and processing errors and errors due to nonresponse. The effects of nonsampling errors are more difficult to evaluate than those that result from sampling variability. As much as possible, procedures are built into surveys in order to minimize nonsampling errors.

The standard error is a measure of the variability due to sampling when estimating a parameter. It indicates how much variance there is in the population of possible estimates of a parameter for a given sample size. Standard errors can be used as a measure of the precision expected from a particular sample. The probability that a sample statistic would differ from a population parameter by less than the standard error is about 68 percent. The chances that the difference would be less than 1.65 times the standard error are about 90 out of 100, and the chances that the difference would be less than 1.96 times the standard error are about 95 out of 100.

Standard errors for percentages and numbers of persons based on CPS data were calculated using the following formulas:

Percentage:

  se = square root of (b/N)(p)(100-p)
where p
N
b
=
=
=
the percentage (0 < p < 100),
the population on which the percentage is based, and
the regression parameter, which is based on a generalized variance formula and is associated with the characteristic.

For 2008, b is equal to 2,131 for the total or White population, 2,410 for the Black population, 2,744 for the Hispanic population, and 2,410 for the Asian/Pacific Islander population ages 14–24. The b for regional estimates are 1.06 for the Northeast, 1.06 for the Midwest, 1.07 for the South, and 1.02 for the West.

CPS documentation explains the purpose and process for the generalized variance parameter:

    Experience has shown that certain groups of estimates have similar relations between their variances and expected values. Modeling or generalizing may provide more stable variance estimates by taking advantage of these similarities. The generalized variance function is a simple model that expresses the variance as a function of the expected value of a survey estimate. The parameters of the generalized variance function are estimated using direct replicate variances (Cahoon 2005, p. 7).

Number of persons:

  se = square root of (bx)(1-(x/T))
where x
T
b
=
=
=
the number of persons (i.e., dropouts),
population in the category (e.g., Blacks ages 16–24), and
as above.

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4 This age range was chosen in an effort to include as many students in grades 10–12 as possible. Because the rate is based on retrospective data, it is lagged 1 year, meaning that some 15-year-olds have turned age 16 by the time of the interview.
5 Age 16 was chosen as the lower age limit because, in some states, compulsory education is not required after age 16. Age 24 was chosen as the upper limit because it is the age at which free secondary education is no longer available and the age at which the average person who is going to obtain a GED does so.
6 Age 18 was chosen as the lower age limit because most diploma holders earn their diploma by this age. Age 24 was chosen as the upper limit because it is the age at which free secondary education is no longer available and the age at which the average person who is going to obtain a GED does so.


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