Traditional Probation & Intensive Supervision ... - Ottawa County

Attachment HSampling ProceduresInterviews were conducted with individuals sentenced to probation during the evaluationperiod in order to gain insight into their experiences in either the Traditional or ISPprogram. A series of questions were asked of the probationers who participated in thephone interview process. Because of the size of the evaluation population (1,572), asampling procedure was utilized to identify probationers who would be contacted for thephone interview.The sampling procedure involved simple random sampling, which ensures that eachperson from the population had an equal chance of being selected for inclusion in thesample. Since the sample will be representative of the population, a standard statisticalprocedure was employed to develop confidence intervals. Confidence intervals specifyboth a precision and a level of confidence with regard to the accuracy of the data obtained.A 95% confidence level was selected for this evaluation, meaning that one can be 95%sure that the data obtained are somewhere within range of the confidence interval. Thestatistical calculations employed for the sampling procedure, which were based on samplesize, population size, and confidence level, yield a +/- 9.5% confidence interval, or marginof error for each question.A sample size of 100 was selected to represent the population of 1,572 probationparticipants in order to achieve the 95% confidence level. Because it was anticipated thatnot every participant would respond and/or be available to participant in the phonesurvey, a pool of 400 probationers were randomly selected from the population in orderto achieve the sample size of 100. A response rate of 25% was estimated for thisevaluation. The random sample of 400 probationers was selected using a randomizerquery written in Microsoft Access. The resulting 400 people were compared to the entirepopulation to ensure that they were truly representative with respect to demographiccharacteristics. The number and percent of contacts made as part of the random samplingprocess are provided in Table 1.Table 1From EntireStudyFrom RandomSampleFromCompletedInterviewsTotal Number of Probationers 1,572 (100.0%) 467 (100.0%) 100 (100.0%)Traditional Probationers 85.2% (1,340) 85.6% (400) 83.0% (83)ISP Probationers 14.8% (232) 14.4% (67) 17.0% (17)Traditional ProbationersCompleted Probation 77.7% (1,041) 80.0% (320) 90.4% (75)Failed to Complete Probation 21.9% (293) 19.8% (79) 9.6% (8)Deceased 0.4% (6) 0.2% (1) 0% (0)ISP ProbationersCompleted Probation 53.0% (123) 56.7% (38) 52.9% (9)Failed to Complete Probation 46.6% (108) 43.3% (29) 47.1% (8)Deceased 0.4% (1) 0% (0) 0% (0)Source: Ottawa County Planning Department