#sampling

Design appropriate sampling strategy and calculate required sample size. Sampling methods: 1. Probability sampling: simple random, systematic, stratified, cluster sampling. 2. Non-probability sampling: convenience, purposive, snowball, quota sampling. 3. Mixed methods: sequential explanatory requires smaller qualitative sample after quantitative phase. Sample size calculation: 1. Continuous outcomes: use power analysis with effect size, alpha=0.05, power=0.80. 2. Categorical outcomes: use proportion formulas with expected proportions and margin of error. 3. Longitudinal studies: account for dropouts, multiply by 1/(1-dropout rate). 4. Cluster sampling: design effect multiplier for correlated observations within clusters. Tools: G*Power, R pwr package, online calculators. Survey research: response rates typically 20-30% for online, 40-60% for phone. Adjust target sample accordingly. Report response rates and compare respondents to non-respondents on available characteristics.