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Formula:
The formula to determine the required sample size (n) for estimating a population proportion (p) with a desired margin of error (e) and confidence level (Z-score) is:
n = (Z2 * p * (1 - p)) / e2
Where:
- n = Required Sample Size
- Z = Z-score corresponding to the desired Confidence Level (e.g., 1.645 for 90%, 1.96 for 95%, 2.576 for 99%)
- p = Estimated Population Proportion (proportion of the population that has a particular characteristic. Use 0.5 if unknown for maximum sample size)
- e = Desired Margin of Error (as a decimal, e.g., 0.05 for 5%)
If the population size (N) is known and relatively small, a finite population correction (FPC) is applied:
ncorrected = n / (1 + ((n - 1) / N))