Homework and Sleep Table: Summary Without Causation
You are preparing a one-paragraph summary for a health newsletter. The table shows results from a survey of 300 students at a high school: Grade 7 - 45 minutes of homework per day, 72% meeting the sleep guideline; Grade 8 - 60 minutes, 65%; Grade 9 - 90 minutes, 48%. A note explains that 'meeting the sleep guideline' means at least 8 hours on school nights. The margin of error is ±4 percentage points, and the survey was conducted in November. The newsletter editor wants a summary that a parent can understand in ten seconds and that does not overstate the evidence. A classmate writes: 'The table proves that more homework causes students to sleep less.'
1. Write one accurate summary sentence (25–35 words) for the newsletter that describes the pattern without implying causation.
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Possible sentence: 'In a November survey of 300 students, the share meeting the 8-hour sleep guideline fell from 72% in Grade 7 to 65% in Grade 8 and 48% in Grade 9, while reported homework time rose from 45 to 90 minutes a day.'
Why this is accurate: it names the sample and date, defines the guideline in the setup, reports the direction of both variables, and uses 'while' rather than 'because'. It does not say homework caused less sleep. It also avoids 'proves', which a single survey cannot do.
2. Explain why the classmate's sentence is not supported, and name two pieces of information that would be needed before making a causal claim.
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The classmate's sentence is unsupported because the table is a cross-sectional survey: it shows that grade level, homework time, and sleep guideline rates differ together, not that one produces the other. Grade 9 students also differ in age, commute, club commitments, screen time, and part-time work; any of these could affect sleep. The ±4 point margin also means the 7-point Grade 7–8 gap is modest. To support causation, we would need at least (a) individual-level or longitudinal data showing that when a student's homework rises, that student's sleep falls, and (b) control for confounders such as bedtime, commute, and screen use.
3. You must cut the summary to 20 words for a poster. Which data will you keep and which will you omit? Justify your choices.
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For a 20-word poster, keep the strongest contrast and the sample: 'Survey of 300 students: 72% of Grade 7 but only 48% of Grade 9 met the 8-hour sleep guideline.' This preserves the trend and the source. Omit Grade 8 and the exact homework minutes: the middle point adds detail but weakens the poster's single message, and the minutes are less meaningful without the guideline. The omission is not misleading because the poster still reports a real comparison; it simply selects the most informative endpoints.