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Sampling methods, bias and study design
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Learn it Simple random: every member equally likely. Stratified: random samples from each group in proportion. Systematic: every kth member. Convenience and voluntary samples are often biased. An experiment imposes a treatment (and can show cause and effect); an observational study only watches.
Example: A survey asks people leaving a gym how often they exercise. Problem?
- Gym-goers exercise more than most people.
- Sampling bias: the sample isn't representative.
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