Statistics · Sampling
Chapter 1 · 3
The idea
Bias & sampling methods
What bias really is — a method that systematically leaves people out, so a bigger sample never fixes it — how to name who is missing, the strengths and weaknesses of random, systematic, stratified and convenience sampling, and how to criticise and rewrite a questionnaire.
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Statistics · Sampling
Bias & sampling methods
What bias really is — a method that systematically leaves people out, so a bigger sample never fixes it — how to name who is missing, the strengths and weaknesses of random, systematic, stratified and convenience sampling, and how to criticise and rewrite a questionnaire.
Why it works
What bias actually is
A sample is a stand-in. You cannot ask all people in a town, so you ask and then talk as if what those said is what the town thinks. That swap is only honest if the are like the town. Bias is what happens when the way you chose them guarantees they are not.Be precise about the word. Bias is not "an unlucky sample", and it is not "too few people". It is a property of the method: a method is biased when it systematically over-represents one part of the population, or leaves another part out altogether. Systematic is the key word: it pushes the answer the same way every time.
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