Abstract A type of hybrid retrospective design for epidemiologic studies within defined populations is considered. The design requires “exposure” information for the complete population of cases and for a random sample of the original population at risk (PAR). Assuming that the only stochastic feature occurs with the random sampling of the PAR, confidence intervals for incidence rates and relative risk (R) are developed in conjunction with PAR sample size requirements. Analysis by stratification is discussed and a numerical example included.
Kupper et al. (1975) studied this question.