U.S. flag

An official website of the United States government, Department of Justice.

Assessing Parole Violation Rates by Means of the Survivor Cohort Method

NCJ Number
Federal Probation Volume: 44 Issue: 4 Dated: (December 1980) Pages: 26-32
G F Davis
Date Published
The survivor cohort method is compared to two other methods for assessing parole violation rates, and the hypothesis that the early months on parole are the most risk prone is examined.
The study sample consisted of the 4,959 youths paroled during 1972 by the California Youth Authority. The followup period was set at 48 months. The first method of calculation utilized the total violators (2,764) as the base and determined the precent of violators by dividing the number of violators each month by the total violators to indicate how long they were on parole at the time of removal. In the second method, the total release cohort (4,959) is the base, and each month's violators are divided by this figure to show what percent violate parole each month. Both methods -- the most commonly used -- seem to support the theory of a higher violation rate during the early months of the parole period. However, neither rate indicates what period of time during the followup period has the highest risk of failure. The survivor cohort method achieves this. This method takes each release cohort for each month of the 12-month period, adds each month's releases to the releases for the previous month, and subtracts the removals for that month in order to get an average number on parole each month. This is used as the denominator of the expression, and the numerator is the number of violators each month. The results demonstrate that violation rates do not change significantly over time. Graphs and footnotes with references are included.