Sampling determines whether your data can actually answer the questions you are asking. Get the sample size wrong and you waste money on a survey that cannot detect real change. Choose the wrong sampling method and your findings do not represent the population you claim to serve. This hub covers the full set of sampling decisions: how many people, selected how, with what adjustments for clustering and non-response, and the common mistakes that undermine even well-designed studies. The Sampling Calculator handles the math; these pages explain the judgment calls behind it.
Side-by-side comparisons, decision trees, and practical guidance for common M&E decisions.