Chapter 4 · Sampling · Slide 141/274

Margin of Error Approach: Two Formulas

The Problem of Unknown Dispersion

4.4 · Sample Size The Problem of Unknown Dispersion

x = true value of the parameter x̂ = sample value E = margin of error

For Metric Data

Means

Assessing means calculated from the sample

Usually unknown E = z · σ / √n — σ highlighted

zz-value for the specified confidence level

σStandard deviation of the parameter in the population

nSample size

For Proportions

Proportions

Assessing calculated proportions

Usually unknown E = z · √(π(1−π)/n) — numerator highlighted

zz-value for the specified confidence level

πEstimate of the proportion in the population

nSample size

QUESTIONSTAR · Dr. Paul Marx 141 / 274