Final answer:
The adequacy of sample size in a qualitative study is defined by the achievement of data saturation, where additional subjects do not provide new insights. Unlike quantitative studies, qualitative research does not primarily use statistical power or fixed numerical criteria to determine sample size.
Step-by-step explanation:
The number of participants or sample size in a qualitative study is adequate when saturation of data is achieved, and additional subjects provide no new information. This principle differs from quantitative research, where sample sizes are often determined by the power of the study, indicated by power analysis, or the need to identify differences between groups statistically. In qualitative research, the emphasis is on gathering rich, detailed information until further interviews or data collection add no further insight into the topic being researched, which is known as data saturation.
In quantitative studies, sample sizes might be calculated using power analysis to achieve a certain power level typically 0.8, ensuring that the study has a high probability of detecting a true effect if one exists. However, qualitative research does not rely on statistical power but rather on the depth and comprehensiveness of the data collected.
Relying on rules of thumb, the concept of saturation is a more qualitative and flexible approach that is determined by the nature of the study and the richness of the data rather than fixed numerical criteria. The process involves continuous assessment of whether new data continue to provide new insights or if they are merely repeating what was already collected.