Patton, M
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چکیده
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 the very logic of each approach is unique because the purpose of each strategy is different. The logic and power of probability sampling depends on selecting a truly random and statistically representative sample that will permit confident generalization from the sample to a larger population. The purpose is generalization. The logic and power of purposeful sampling lies in selecting in formation-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 research, thus the term purposeful sampling. For example, if the purpose of an evaluation is to increase the effectiveness of a program in reaching lower-socioeconomic groups, one may learn a great deal more by focusing in depth on understanding the needs, interests, and incentives of a small number of carefully selected poor families than by gathering standardized information from a large, statistically representative sample of the whole program. The purpose of purposeful sampling is to select information-rich cases whose study will illuminate the questions under study. There are several different strategies for purposefully selecting information-rich cases. The logic of each strategy serves a particular evaluation purpose. (1) Extreme or deviant case sampling. This approach focuses on cases that are rich in information because they are unusual or special in some way. Unusual or special cases may be particularly troublesome or especially enlightening, such as outstanding successes or notable failures. If, for example, the evaluation was aimed at gathering data help a national program reach more clients, one might compare a few project sites that have long waiting lists with those that have short waiting lists. If staff morale was an issue, one might study and compare high-morale programs to low-morale programs.
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تاریخ انتشار 2002