A fair sample — Data, 7–10
A small, fairly chosen group can give clues about a much larger group. Data, 7–10 years.
Learning from part of a group
A sample is a smaller group chosen to tell us something about a larger group. We might ask 30 pupils about packed lunches instead of asking every pupil in a town. The sample should include different kinds of people from the larger group, not just the easiest people to find.
Why not ask everyone?
Asking every person can take too long, cost too much or be impossible. A carefully chosen sample gives an answer sooner, so long as we remember that it is evidence about the larger group, not a perfect count of every person. The way people are chosen matters as much as their number.
Spotting a biased sample
A school wants to know which sport pupils prefer. It asks 40 children at football practice: 32 choose football and 8 choose another sport. This sample is easy to collect, but it misses pupils who do not attend football. Asking pupils from several activities would give a fairer picture.
A large sample can still be unfair
It is tempting to trust a survey because it asked many people. But asking 500 football players about the favourite sport may still favour football. This mistake is reasonable: more answers usually help, yet a repeated one-sided choice can make a large sample misleading.
Samples in the world
Companies may test a small number of people before making many biscuits or designing a new toy. Scientists may study a sample of water from a lake rather than emptying the whole lake. A useful sample saves effort, but its limits should be stated honestly.
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