Related Resources: calculators
Sample Size Calculator for Prevalence Studies
Sample Size Calculator for Prevalence Studies, using random (not cluster) sampling.
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Formula WITHOUT finite population correction:
Formula WITH finite population correction:
Daniel WW (1999). Biostatistics: A Foundation for Analysis in the Health Sciences. 7th edn. New York: John Wiley & Sons.
Step 1: Enter the expected P in proportion of One. (For example, if the expected prevalence is 30%, then P =0.3).
Step 2: Enter the population size ( N ) (maybe an estimate) from which the sample will be taken. (If the population size is very large but not known exactly (i.e. infinite population), then LEAVE IT BLANK).
Step 3: Decide the sample size ( n ) from the Sample Size Table based on desired precision. The second column is the sample size without using finite population correction (FPC) and the third is using FPC. We should use FPC if n / N is >.05 (Daniel, 1999). Suggestion is given in the 4th column.
Calculated sample size should meet the normal approximation assumption (Daniel, 1999). The 5th column reports about this assumption.