The required sample size depends on various factors, including the research design, the population size, the expected effect size, the desired power of the study, and the acceptable margin of error.
For a simple random sample, the sample size (n) can be calculated using the following formula for proportions:
n=Z^2⋅p⋅(1−p) / E^2
Where:
- Z is the Z-value (the number of standard deviations from the mean corresponding to the desired confidence level, e.g., 1.96 for 95% confidence)
- p is the estimated population proportion
- E is the margin of error
For finite populations, adjust the sample size using:
n= n / 1+(n-1/N)
Where:
- N is the population size.
You can also use;
Software and Online Calculators
You can also use statistical software like G*Power, or online sample size calculators, which can simplify the process and account for more complex study designs.
Consulting a Statistician
Consulting with a statistician is recommended to ensure the sample size is appropriately calculated for more complex studies, especially those involving multiple groups, stratification, or advanced statistical analyses.
Charan J, Biswas T. How to calculate sample size for different study designs in medical research?. Indian J Psychol Med 2013;35:121-6.
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