Continuous observation work sampling and its verification

Work sampling focuses mainly on determining the proportion of times for a specified category within a predetermined tolerance at a specified statistical risk. Conventional practices are based on numerous snap (instantaneous) observations taken randomly. This study employs the extensively used method of "production study" or so-called continuous observation work sampling (COWS). Data from continuous observation of activity are used to make point estimates of the average time spent in each category and also the proportion of time occupied by a specified category. This study concentrates mainly on determining and verifying the interval estimates that derived from two different process assumptions, alternating Poisson process (APP) and alternating unspecified process (AUP), for a proportion when using COWS. Simulation results indicate that the confidence interval formulae derived for AUP assumptions are robust if the sample sizes for both modes exceed 100. Although the exact formulae are derived from APP, poor results yield if the true process deviated from APP.