Sampling Size
Sampling Strategy and Sample Size for a Qualitative Research Plan
A grounded theory perspective on the victimization of women and human trafficking
The formulas for determining appropriate sampling sizes for quantitative research studies are fairly formalized, given the need to make generalizations about the macro-level population based upon the findings of these experimental or quasi-experimental studies. However, the purpose of qualitative studies is to come to conclusions based upon the researcher's inductive findings regarding a specific group of people. For an ethnographic study, the 'sample size' of the population might constitute a very small tribe. A narrative qualitative study might involve discussing the findings of studying a small class of children. The purpose of qualitative studies is to let the experiences of individuals speak for themselves, whether this takes the form of a case study, a narrative of a specific handful of participants, or simply 'making meaning' from a culture. Although I would hope that my grounded theory study on women who had been trafficked into the sex trade or economic slavery would yield findings that would be helpful in giving assistance to such women in the future and contribute to my reader's general understanding of the topic, my ultimate purpose is still to let these women speak, and the theory will derive from their experiences. My hypothesis as a researcher should not drive and shape the findings.
In general, with quantitative research, larger sampling sizes are preferable, given the 'law of large numbers' or the idea that large samples are less prone to exhibit errors because of anomalies. But "there is a point of diminishing return to a qualitative sample -- as the study goes on more data does not necessarily lead to more information. This is because one occurrence of a piece of data, or a code, is all that is necessary to ensure that it becomes part of the analysis framework" (Mason...
The point of qualitative research is to embark up on the intensive study of specific phenomenon, not to create broad generalizable conclusions. However, it is also true that it is not necessarily the case that 'smaller is better,' either. "Qualitative samples must be large enough to assure that most or all of the perceptions that might be important are uncovered" (Mason 2010:1).
The principle of sampling size in qualitative sampling is one of saturation, or the concept that new data "does not shed any further light on the issue under investigation" which will be determined by "heterogeneity of the population; the number of selection criteria; the extent to which 'nesting' of criteria is needed; groups of special interest that require intensive study; multiple samples within one study; types of data collection methods use; and the budget and resources available" (Mason 2010: 1-1.1). In the case of my research study, the population of women who are frequently victims of trafficking is heterogeneous to some degree in that women from many different nations may be trafficked and there may be 'special' groups which deserve additional consideration, such as women who are trafficked into the sex trade vs. domestic and economic servitude or women who are compelled to remain with their abductors through physical violence and threats of physical violence vs. women who remain with their abductors primarily due to psychological intimidation.
By and large, most women who are trafficked come from poorer, developing world nations. Most are duped into their situation with promises of a better opportunity than exist in their homeland. But there are other factors to consider when creating a sampling size, namely: "the scope of the study, the nature of the topic, the quality of the data, the study design" the scope of the study, the nature of the topic, the quality of the data, the study design" (Mason 2010: 1.1). For example, my study will by virtue of necessity limited…
