Foundation and Higher · sampling

You cannot ask
everyone. So ask
a fair sample.

and know its
limits

a small group standing for the whole —

Sample

chosen from the population

it must be fair

card 1 of 6

Population

Everyone or everything you want to find out about.

every student in the school

card 2 of 6

Sample

A smaller group chosen from the population.

quicker and cheaper to ask

card 3 of 6

Random sample

Every member has an equal chance of being chosen.

names out of a hat

card 4 of 6

Bias

A sample that does not represent the population fairly.

only asking your own friends

card 5 of 6

Sample size

10 people → shaky
200 people → reliable

A bigger sample gives more reliable results.

but it takes longer

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Scaling up

1250 × 600 = 144

12 of a sample of 50 walk to school. Estimate for all 600 students.

same proportion, bigger group

sampling —

Random

everyone has an equal chance

Biased

some groups are left out

Bigger sample

more reliable

A sample only gives
an estimate.

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