Some say 30% of population for qualitative research
Others say any sample size for quantitative research is good enough
Please share your ideas on the question, both in qualitative and quantititaive research methods
The sample size must be representative to the population. The bigger sample size gives more trusted results.
Just to add to what Abdallah said. There are specific methods that you can consider in determining adequate sample size. These methods considers a number of things 1) The primary research question 2) Your research design e.g cross section, case control, cohort etc 3) Clinically significant difference i.e. How much difference can be considered clinically relevance. It is important to note that 'a difference to be a difference MUST make a difference' 4) The degree of certainty for finding that difference (power) 5)Level of significance or type 1 error and 6) Measure of variation
Now based on specific study design, you can adopt specific formula to calculate a sample size. The formula can be obtained from a book by Daniel, Wayne W. Biostatistics: a foundation for analysis in health science pg 177-80. (attached)
It is also worth noting that, too small sample will fail to detect clinically important effect (have less power) where as too large sample will give a statistically significant differences which has no clinical relevance. Both of these scenarios are inappropriate in research.
Although sample size is a consideration in qualitative research, the principles that guide the determination of sufficient sample size are different to those that are considered in quantitative research.
In quantitative research, sufficient sample size is the minimum number of participants required to identify a statistically significant difference if a difference truly exists. Elements that influence sample size include the effect size, the homogeneity of the sample, the risk of error considered appropriate for the question being studied. Sample size calculation can be achieved using different methods details in (https://research-repository.griffith.edu.au/bitstream/handle/10072/51545/83704_1.pdf?sequence=1&isAllowed=y)
For qualitative research
The purpose of qualitative research methods is to look for meaning (i.e. to understand the why and how behind things). The sample of people or situations required for qualitative research methods is therefore small in number (relative to the sample required for quantitative research methods) but includes the widest range of people or situations (rather than being representative).( https://www.ageuk.org.uk/globalassets/age-uk/documents/reports-and-publications/reports-and-briefings/guidance-- sample_size_estimation_for_qualitative_methods_april2017.pdf )
In statistical books, there may be separated chapters about Sample Size such as
(http://vanbelle.org/chapters%5Cwebchapter2.pdf )
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