부산대학교 도서관

Hourglass Sampling of Participants in the Human Reliability Program (HRP) for Alcohol and Drug Testing Ivan R. Thomas Idaho National Laboratory The random sampling with replacement of Human Reliability Program (HRP) participants for alcohol and drug testing can have the disadvantage that some participants are selected multiple times while others might not be chosen during an annual testing period. To alleviate this inefficiency, an “hourglass” sampling scheme has been developed at the Idaho National Laboratory for the random selection of HRP participants. With this scheme, all HRP participants are placed in a primary population at the beginning of the calendar year, and throughout the year, sequential random samples (generally of a fixed sample size) are drawn without replacement until the population is emptied. Thus, each participant is guaranteed to be tested at least once annually; but due to the random selection, the time of the initial test is unknown. After initial testing, the participants drawn from the primary population are transferred to a secondary population for potential retesting. Each time that the primary population is sampled, the secondary population is likewise sampled, but the sampling is with replacement. Thus, while the primary population decreases at a constant rate, the secondary population increases at the same rate through the accrual and retention of previously-tested participants, hence the hourglass concept. The replacement sampling of participants from the secondary population is through an increasing sample size (a fixed percentage of those currently in the population). Thus, once in the secondary population, each participant has a constant probability of being reselected, but the number of annual reselections is less than would be realized through traditional replacement sampling from a single population. Furthermore, the objective of maintaining suspense on the part of the HRP participant is retained, that is, all participants, whether or not initially picked from the primary population or reselected from the secondary population, always anticipate a future selection.