In qualitative methodology, the sample size is really not important because the purpose of qualitative methodology is depth of meaning or insight that leads to new theoretical formulations or frameworks. Power analysis can inform quantitative research about the required sample size to determine a small, medium, or large effect for a specific statistical test, but nothing similar is available for qualitative research.
In theory, qualitative researchers should continue data collection until such time as they have reached saturation or the point at which they are no longer hearing new insights from their participants. One flaw I often note in qualitative manuscripts is a lack of focus on this very point. Until the researcher begins to intentionally seek out negative evidence or alternative explanations from the research participants, I do not personally see how saturation can be reached. Of course, others may have different perspectives on this.
In qualitative methodology, the sample size is really not important because the purpose of qualitative methodology is depth of meaning or insight that leads to new theoretical formulations or frameworks. Power analysis can inform quantitative research about the required sample size to determine a small, medium, or large effect for a specific statistical test, but nothing similar is available for qualitative research.
In theory, qualitative researchers should continue data collection until such time as they have reached saturation or the point at which they are no longer hearing new insights from their participants. One flaw I often note in qualitative manuscripts is a lack of focus on this very point. Until the researcher begins to intentionally seek out negative evidence or alternative explanations from the research participants, I do not personally see how saturation can be reached. Of course, others may have different perspectives on this.
Peter makes some excellent points here. His last point is one that I can in agreement with especially. In order to increase the credibility of your findings, you have to spend time trying to seek out evidence that your explanatory conclusion may account for various data points. Throughout qualitative methodologies this point has always been touted but I often see manuscripts come to our journal (Journal of Interactional Research in Communicative Disorders) or other qualitative journals without any mention of this type of verification. His point about the differences between quantitative and qualittive research in terms of sample size and WHY one focuses on sample size in quantitative research using predictive statistics is quite accurate.
In my opinion, it is a bit confusing when we say 'qualitative approach'. The difference between qualitative data and qualitative approaches is often overlooked Very often we tend to confuse inductive and interpretive research with qualitative data. In this, I don't agree with Peter, I mean if you are following a positivist approach, then even if you are dealing with some sort of qualitative data, you still have to make sure a sufficient number of respondents, for the sake of generalizability. In this case, the criteria for minimum number of respondents should be the same as it is for quantitative data. However, if by qualitative approach you mean inductive or interpretive approach, then what Peter and Jack have said above is much enlightening already.