Statistics › Section A · Sampling and data › Topic A.2
Data, sampling, and variation
Data are only as good as the way they were gathered. This topic covers the standard sampling designs, the ways samples go wrong, and why two fair samples rarely agree exactly.
In this topic
- Where data come from
- Sampling variability
- Simple random samples
- Stratified, cluster, and systematic designs
- Convenience and voluntary response samples
- Bias inside a well-run sample
- Worked example: naming the design
- Worked example: two samples, two answers
- A famous failure: the 1936 Literary Digest poll
- Common mistakes to avoid
- Key takeaways
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