Why are Tom's data and the internet data not completely comparable?
How to approach this question
1. Look for differences between Tom's study and the internet chart.
2. Tom's study group: "Year 11 students".
3. Internet chart study group: "15-year-olds".
4. Consider if these two groups are identical. A student in Year 11 could be 15 or 16. A 15-year-old could be in Year 10 or Year 11.
5. This difference in the definition of the group makes the data not completely comparable.
6. Other possible reasons: Tom's data is from one school vs national/international data; the internet data is unsourced and may be old.
Full Answer
The age groups are different. Tom's data is for Year 11 students, while the internet chart is for 15-year-olds. These groups are not exactly the same.
For data sets to be directly comparable, they should be collected under similar conditions from similar populations. There are several reasons for a lack of comparability here:
- **Population Mismatch**: Tom's data is for "Year 11 students". The internet data is for "15-year-olds". While there is a large overlap, a Year 11 student can be 16, and a 15-year-old can be in Year 10. The populations are not identical.
- **Scope**: Tom's data is from a single school, which may not be representative of the entire UK. The internet data represents a national average. Comparing a specific case to a general average can be misleading.
- **Time Frame**: We don't know when the internet data was collected. It could be from a different year to Tom's study, and homework amounts may have changed over time.
Common mistakes
✗ Vague answers like "the data is different".
✗ Focusing on the fact the internet chart has no source (this relates to reliability, which is the next question).
Expert