T4W7 TS Q37 – Selective High School

Mr Henderson conducts a year-long study on whether student sleeping patterns change depending on age.

He studies two groups of 20 students each.
The first group has children aged 7 to 13.
The second group has children aged 9 to 15.

He finds that the first group of students sleep on average 15 minutes longer than the second group.

He concludes that the younger the age, the longer the students sleep on average.

Which of the following statements shows the mistake Mr Henderson has made?

The age groups of the participating students were too far apart to have an accurate result. Mr Henderson's subjects did not record their sleep patterns accurately, which may have skewed the results. There is an overlap of ages between the two age groups. Mr Henderson has not studied the two groups for a long enough period.

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Which of the following statements shows the mistake Mr Henderson has made?