Needles in Haystacks and Diamonds in the Rough: Using Probability and Nonprobability Methods to Survey Low-incidence Populations

While probability samples are generally the preferred approach in survey research, nonprobability samples continue to be of interest and are used for multiple purposes. We discuss the use of a convenience sample in one study and social media recruitment in another when probability-based samples fell short of reaching target sample sizes for low-incidence populations. Both studies collected rich survey data, particularly regarding household finances, enabling comparisons between respondents in the two types of samples. Analysis shows that while demographic characteristics were not consistent across the two types of samples, the source of the data—the probability sample or the nonprobability sample—was not significant in predicting the primary research variables of interest. We conclude that combining cases from the two types of samples may be appropriate for analyses in these studies. We suggest that nonprobability samples may be particularly appropriate for low-incidence populations; we also suggest that similar techniques may be useful for other researchers as they investigate the utility of nonprobability samples