Worked example · PSE / Well-being · Year 8
DCF: Data and computational thinking → Data and information literacy
A secure Year 8 response, annotated. Every formula and every answer below is correct for the seven rows in sample-habits-week.csv, so you can mark from this sheet without checking the arithmetic yourself. If a pupil’s number differs, the usual cause is a range of B2:B9 instead of B2:B8, which pulls in an empty row.
| Row | A | B | C | D | E | F | G |
|---|---|---|---|---|---|---|---|
| 1 | Day | Sleep hours | Active minutes | Water glasses | Screen time minutes | Mood 1–5 | Sleep target |
| 2 | Monday | 7.5 | 45 | 5 | 180 | 3 | Below target |
| 3 | Tuesday | 8 | 60 | 6 | 150 | 4 | Target met |
| 4 | Wednesday | 6.5 | 30 | 4 | 240 | 2 | Below target |
| 5 | Thursday | 8.5 | 75 | 7 | 120 | 4 | Target met |
| 6 | Friday | 7 | 90 | 6 | 200 | 4 | Below target |
| 7 | Saturday | 9 | 105 | 8 | 300 | 5 | Target met |
| 8 | Sunday | 8.5 | 15 | 5 | 140 | 3 | Target met |
Column G was added by the pupil and filled by dragging one formula down, not by typing seven words. The formula is in the table below.
| What you need to find out | The formula typed | The answer |
|---|---|---|
| Total sleep for the week | =SUM(B2:B8) | 55 hours |
| Mean sleep per night, to 2 d.p. | =ROUND(AVERAGE(B2:B8),2) | 7.86 hours |
| Best and worst night’s sleep | =MAX(B2:B8) and =MIN(B2:B8) | 9 hours (Saturday) and 6.5 hours (Wednesday) |
| Total active minutes for the week | =SUM(C2:C8) | 420 minutes |
| Mean active minutes per day | =AVERAGE(C2:C8) | 60 minutes exactly |
| How many days hit the 60-minute target | =COUNTIF(C2:C8,">=60") | 4 days — Tuesday, Thursday, Friday, Saturday |
| Mean screen time per day | =AVERAGE(E2:E8) | 190 minutes, which is 3 hours 10 minutes |
| Mean mood score, to 2 d.p. | =ROUND(AVERAGE(F2:F8),2) | 3.57 out of 5 |
| A column printing “Target met” or “Below target” for sleep | =IF(B2>=8,"Target met","Below target") in G2, dragged to G8 | 4 days met, 3 below (Monday, Wednesday, Friday) |
Every formula uses a cell range rather than typed-in numbers, and the right function is matched to the right question — SUM for a total, AVERAGE for a mean, COUNTIF for “how many days”. That is the first and second criterion.
Sleep: 7.5 + 8 + 6.5 + 8.5 + 7 + 9 + 8.5 = 55, and 55 ÷ 7 = 7.857…, so 7.86 to two decimal places.
Activity: 45 + 60 + 30 + 75 + 90 + 105 + 15 = 420, and 420 ÷ 7 = 60 exactly. So the week hits the national average target on the nose, even though only four of the seven individual days do.
Screen time: 180 + 150 + 240 + 120 + 200 + 300 + 140 = 1330, and 1330 ÷ 7 = 190.
Mood: 3 + 4 + 2 + 4 + 4 + 5 + 3 = 25, and 25 ÷ 7 = 3.571…, so 3.57.
| Cells the rule applies to | C2:C8 — the Active minutes column only |
|---|---|
| The condition | “Format cells if… Less than” with the value 60. In Excel this is Home → Conditional Formatting → Highlight Cells Rules → Less Than; in Google Sheets it is Format → Conditional formatting → Less than. |
| The formatting applied | Red fill with dark red bold text, so it is visible in colour and still readable if the sheet is printed in greyscale. |
| How many cells changed colour, and which days | 3 cells: Monday (45), Wednesday (30) and Sunday (15). Tuesday is 60, which is not less than 60, so it correctly stays unhighlighted. |
Uses the real 60-minute guideline, and notices the boundary case: Tuesday on exactly 60 is not highlighted. Getting that edge right is the difference between copying a rule and understanding one. This is the third criterion.
| Chart type | Column chart (vertical bars), one bar per day |
|---|---|
| Horizontal axis | Day of the week, Monday to Sunday, in order |
| Vertical axis | Active minutes, scaled 0 to 120 |
| Chart title | “Active minutes per day against the 60-minute target” |
| Why not a pie chart | A pie chart shows parts of a whole. These seven numbers are not parts of one thing, they are seven separate measurements of the same thing over time — and a pie chart cannot show a target line at 60. |
Titled, both axes labelled with units, and the chart type is justified by what the data is. The target-line point is the strongest reason given.
Conclusion 1 — supported by the data. This week averaged exactly 60 active minutes a day, which meets the UK guideline, but the average hides the pattern: only 4 of the 7 days reached 60 minutes, and Sunday managed 15. Saturday alone contributed 105 of the 420 minutes. So the weekly average is met by two good days carrying three poor ones, which is worth knowing if the aim is a habit rather than a total.
Conclusion 2 — not supported by the data. I expected more screen time to mean a worse mood. It does not show that here. =CORREL(E2:E8,F2:F8) gives 0.19, which is a very weak relationship, and in the positive direction — the opposite of what I predicted. Saturday is the clearest case: it has the highest screen time of the week at 300 minutes and also the highest mood score of 5. Sleep looks more promising, since =CORREL(B2:B8,F2:F8) gives 0.68, but seven days of one person’s invented week cannot prove that sleep causes mood. It could just as easily be that a better mood makes it easier to sleep, or that both follow from something I have not measured, such as whether it was a school day.
One conclusion the data supports and one it refuses, both quoting numbers, and the second correctly separates correlation from cause and offers two alternative explanations. This is the fifth criterion, and it is where most of the marks sit.