The Survey on School Start Times
A school council surveys parents about moving the school start time from 8:45am to 9:30am. The survey is sent by email to all 900 families, and 180 responses are received. Of these, 132 support the later start. The council announces that '73% of parents support the change'. A parent points out that families who rely on the current start time to fit their work commute may have been less likely to respond, and that the email list may not reach all families. Separately, teachers report that 40% of students arrive before 8:30am because of parent work schedules.
1. Evaluate the council's claim that 73% of parents support the change.
Read the worked answer
The 73% figure (132 ÷ 180) is arithmetically correct for respondents but not a valid estimate of all parents.
Problems:
- Response rate is low: 180 of 900 = 20%. A 20% response cannot be assumed representative.
- Self-selection bias: parents with strong views (for or against) are more likely to reply. The parent's point is sharper: families whose commute depends on the 8:45 start may have been less likely to respond, which would inflate apparent support.
- Coverage: if the email list misses some families, those voices are absent.
So the defensible statement is '73% of the 180 parents who responded support the change', not '73% of parents'. The council has overgeneralised from a biased sample.
2. Given the teachers' report, what does the 40% figure imply for the decision?
Read the worked answer
If 40% of students arrive before 8:30am because of parent work schedules, a 9:30am start would create a childcare and supervision gap for a large minority of families - arriving at 8:30 for a 9:30 start leaves an hour unaccounted for.
This matters because the survey's apparent support may not reflect these families' constraints, and the school would need to provide supervised early arrival, which has cost and staffing implications. The 40% figure is a constraint, not a vote: it tells the council that any later start must be paired with a plan for early arrivers.
The judgement being tested: recognising that a policy can be popular among respondents yet impractical for a substantial group whose needs the survey failed to capture. A good answer links the survey bias to this concrete operational problem.