Snowball Sampling

Snowball sampling may be defined as a technique for gathering research subjects through the identification of an initial subject who is used to provide the names of other actors. These actors may themselves open possibilities for an expanding web of contact and inquiry. The strategy has been utilized primarily as a response to overcome the problems associated with understanding and sampling concealed populations such as the deviant and the socially isolated (Faugier & [Page 1044]Sargeant, 1997). Snowball sampling can be placed within a wider set of methodologies that takes advantage of the social networks of identified respondents, which can be used to provide a researcher with an escalating set of potential contacts.

Snowball sampling is something of a misnomer for a technique that is conventionally associated more often with qualitative research and acts as an expedient strategy to access hidden populations. The method has suffered an image problem in the social sciences given that it contradicts many of the assumptions underpinning conventional notions of random selection and representativeness. However, the technique offers advantages for accessing populations such as the deprived, the socially stigmatized, and the elite. In his study of political power and influence in South London, Saunders used a reputational method and asked his contacts to refer him to others who were viewed as holding power in the area (Saunders, 1979). This yielded important but also potentially selfcontained systems of social contact but acted as a valuable insight into the perceptual basis of political power.

Snowball sampling has also advanced as a technique, and the literature contains evidence of a trend toward more sophisticated methods of sampling frame and error estimation and growing acceptance as a tool in the researcher's kit. Shaw, Bloor, Cormack, and Williamson (1996) illustrate these issues in their use of snowball sampling to estimate the prevalence of hard-to-find groups such as the homeless. Here, a technique viewed as a limited qualitative tool is highlighted as a systematic investigative procedure with new applications in the social sciences. However, although selection bias may be addressed through the generation of larger sample sizes and the replication of results, there also remain problems of gatekeeper bias, whereby contacts shield associates from the researcher. However, other groups may themselves consist of highly atomized and isolated individuals whose social network is relatively impaired, further problematizing contact with others.

Snowball sampling can be applied for two primary purposes: first, as an informal method to reach a target population where the aim of a study may be exploratory or novel in its use of the technique, and second, as a more formal methodology for making inferences with regard to a population of individuals that has been difficult to enumerate through the use of descending methodologies such as household surveys. Early examples of the technique can be seen in classics such as Whyte's Street Corner Society, which used initial contacts to generate contexts and encounters that could be used to study the gang dynamic (although there has been a general move away from participant observation of this kind toward the use of snowball sampling techniques for interview-based research more recently).

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