GB-30-02-001 · Sampling bias
A council wants to estimate how often all residents swim. It asks 69 people leaving a swimming pool between 10:00 and 11:00 on a weekday. Give two reasons why this method may produce a biased sample.
Sampling Bias
Supplementary GCSE method — not covered in this booklet
Method
Identify
1) Location bias (over-represents users of that venue) and
2) Time bias (excludes people at work/school)
Worked Example (GB-30-02-001)
1)
The location favours swimmers rather than all residents.
2)
The weekday morning excludes some demographic groups. A small sample alone is not a reason for bias.
Ans =
It over-represents swimmers; the time excludes many residents at work or school.