Blackwell Reference Online

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Perhaps nothing better captures the difference between quantitative and qualitative methods than the different logics that undergird sampling approaches. Qualitative inquiry typically focuses in depth on relatively small samples, even single cases (n = 1), selected purposefully . Quantitative methods typically depend on larger samples selected randomly. Not only are the techniques for sampling different, but also the very logic of each approach is unique because the purpose of each strategy is different. The logic and power of random sampling derives from statistical probability theory. In contrast, the logic and power of purposive sampling lies in selecting information-rich cases for study in depth. Information-rich cases are those from which one can learn a great deal about issues of central importance to the purpose of the inquiry, thus the term purposive sampling (or alternatively, purposeful sampling). What would be “bias” in statistical sampling, and therefore a weakness, becomes intended focus in qualitative sampling, and therefore a strength. Studying information-rich cases yields insights and in-depth understanding rather than empirical generalizations. For example, if the purpose of a program evaluation is to increase the effectiveness of a program in reaching lower-socioeconomic groups, one may learn a great deal more by studying in depth a small number of carefully ... log in or subscribe to read full text