RESUMEN
This paper compares the efficiencies of two sampling techniques for estimating a population mean and variance. One procedure, called grab sampling, consists of collecting and analyzing one sample per period. The second procedure, called composite sampling, collectsn samples per period which are then pooled and analyzed as a single sample. We review the well known fact that composite sampling provides a superior estimate of the mean. However, it is somewhat surprising that composite sampling does not always generate a more efficient estimate of the variance. For populations with platykurtic distributions, grab sampling gives a more efficient estimate of the variance, whereas composite sampling is better for leptokurtic distributions. These conditions on kurtosis can be related to peakedness and skewness. For example, a necessary condition for composite sampling to provide a more efficient estimate of the variance is that the population density function evaluated at the mean (i.e.f(µ)) be greater than[Formula: see text]. If[Formula: see text], then a grab sample is more efficient. In spite of this result, however, composite sampling does provide a smaller estimate of standard error than does grab sampling in the context of estimating population means.
RESUMEN
The annual incidence rates of cervical intraepithelial neoplasia (CIN), grades I to III, from 1975 to 1983 among 2440 prisoners in British Columbia for whom a history of screening by means of the Papanicolaou test was available were two to three times higher than the expected rates in the general female population of British Columbia. The rates among the prisoners from 1970 to 1984, although small, increased with a trend similar to that in the general population. Despite increases in the general population we conclude that prisoners are still at high risk for CIN.