How do you determine sample size?
For a proportion, sample size depends on the confidence level, margin of error and expected proportion. A finite population can then reduce the required sample.
Base formula: n = z² × p × (1 − p) ÷ e². Use p = 0.5 when no prior estimate is available because it gives the most conservative size.
Example: 95% confidence, 5% margin of error and p = 0.5 gives about 385 responses before finite-population adjustment.
This basic calculation assumes a random sample and does not replace a study-specific statistical power analysis.
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