Sample Size & Margin of Error

Also known as: Sample Size, Margin of Error, Confidence Margin, n

Number of respondents needed to obtain statistically significant results at a defined confidence level and margin of error.

Sample Size (n) is the number of units (people, households, establishments) included in a research study. Margin of Error is the range within which the true population value is estimated to fall, with a given confidence level (typically 95%).

Simplified formula for proportions: n = Z²×p×(1-p)/E², where Z is the critical value (1.96 for 95% confidence), p is the expected proportion (0.5 if unknown), and E is the desired margin of error.

Practical rules in market research: n=200 for analysis subgroups, n=400 for reliable global results, n=1000+ for results with ≤3 percentage point margin of error. Sample size has diminishing marginal returns: doubling n from 400 to 800 reduces margin of error from 4.9% to 3.5%, not to 2.5%.