Samples that answer a question — Data, 11–13 years
A survey is useful only when its questions and its group of people fit the thing you want to know.
Ask a fair group
Data begins with a question, such as “How do pupils travel to school?” You usually cannot ask everyone, so you choose a sample. A useful sample resembles the larger group in ways that matter for the question.
Why not ask everyone?
The problem is time, cost and access: a school, town or website may contain far too many people. A sample gives an estimate without asking everyone. It came from the need to learn about a whole population while measuring only a manageable part of it.
A school survey
A school has 600 pupils and wants to estimate how many walk to school. First, choose 60 pupils from different year groups, not just friends. Next, ask the same short question and count the answers. If 18 walk, the sample estimate is 18/60 = 30%, or about 180 of the 600 pupils.
The easy sample
A common mistake is asking only the people who are nearest, quickest to contact or most like you. That feels sensible because it saves effort, but their answers may differ from everyone else's. A sample can be large and still be biased if important groups are missing.
Where samples are used
Opinion polls use samples to estimate what a larger population thinks. Scientists may test a treatment on a selected group before studying its wider effects. Market researchers also sample customers, but the conclusion should say “among this sample” unless the method supports a wider claim.
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