Interpreting a sample’s limitations
Interpreting a sample’s limitations.
- Check who was included, how many responded, when data were collected and who might be missing.
- Sample results are estimates; another random sample can give different results.
- Link the limitation to the claim being made.
Example 1
A random sample of 30 students gives 60% in favour of a proposal. Must exactly 60% of the whole school agree?
Different random samples can give different results.
Example 2
A large survey includes only adults from one town. Can it safely describe all adults in the country?
A large sample does not automatically cover the target population well.
Your turn
A random sample is selected, but only half reply. What is one concern?
Check answer
Random selection cannot force the final responding group to be representative.
A travel survey from ten years ago is used to estimate current habits. Give a limitation.
Check answer
Check when the observations were made.
Only 5 people are surveyed to estimate a town’s favourite sport. Why is the estimate uncertain?
Check answer
A larger, well-selected sample generally reduces random sampling variation.
A company surveys current customers about why people stopped buying from it. Explain the problem.
Check answer
The sampling frame does not cover the group needed for the question.
A random sample finds that students who exercise more tend to score higher. Can the survey prove exercise causes higher scores?
Check answer
Other factors, such as sleep or study habits, could affect both variables.
A random sample is selected, but only half reply. What is one concern?
AnswerRandom selection cannot force the final responding group to be representative.
A travel survey from ten years ago is used to estimate current habits. Give a limitation.
AnswerCheck when the observations were made.
Only 5 people are surveyed to estimate a town’s favourite sport. Why is the estimate uncertain?
AnswerA larger, well-selected sample generally reduces random sampling variation.
A company surveys current customers about why people stopped buying from it. Explain the problem.
AnswerThe sampling frame does not cover the group needed for the question.
A random sample finds that students who exercise more tend to score higher. Can the survey prove exercise causes higher scores?
AnswerOther factors, such as sleep or study habits, could affect both variables.