Worked example · Geography · Year 9
DCF: Data and computational thinking → Data and information literacy
Every statistic worked out from Table 1 on the worksheet, with the totals shown so you can check any figure on a calculator in a few seconds. The data is real Met Office station data for 2023, so these answers are the only correct ones. Show this after pupils have finished their own statistics table.
The wettest single month at any station was Aberporth in December, 168.4 mm. The driest was Ross-on-Wye in February, 7.2 mm — and February was the driest month at all three stations (23.2 mm at Valley, 17.2 mm at Aberporth).
Reading the table accurately before any calculating starts — and noticing that the driest month is the same everywhere, which is a pattern rather than a coincidence.
| Statistic | Valley | Aberporth | Ross-on-Wye |
|---|---|---|---|
| Mean temperature (°C) | 14.4 (173.0 ÷ 12 = 14.4167) | 13.8 (165.7 ÷ 12 = 13.8083) | 15.8 (189.1 ÷ 12 = 15.7583) |
| Median temperature (°C) | 13.75 | 13.3 | 15.15 |
| The two middle values used | 12.4 (Apr) and 15.1 (Oct) | 11.9 (Apr) and 14.7 (Oct) | 13.5 (Apr) and 16.8 (Oct) |
| Temperature range (°C) | 11.9 (21.1 − 9.2) | 11.5 (20.1 − 8.6) | 14.9 (23.7 − 8.8) |
| Total rainfall (mm) | 986.2 | 951.8 | 829.4 |
| Mean summer temperature (°C) | 19.5 (58.6 ÷ 3) | 18.9 (56.7 ÷ 3) | 21.8 (65.5 ÷ 3) |
| Mean winter temperature (°C) | 9.8 (29.5 ÷ 3) | 9.3 (27.9 ÷ 3) | 10.0 (30.1 ÷ 3) |
| Summer minus winter (°C) | 9.7 | 9.6 | 11.8 |
Meets criteria 1 and 2. Each mean shows the total that was divided by 12, and each median names the two middle values that were halved — with twelve readings there is no single middle month, so April and October are averaged.
Within a single station no temperature is repeated at all, so each station's twelve readings have no mode. Across all 36 readings only four values occur twice — 10.6 °C, 10.8 °C, 18.3 °C and 21.1 °C — and nothing occurs three times, so the raw set is multi-modal: four joint modes, which is the same as no useful mode. That is what measuring to 0.1 °C does.
Rounded to the nearest whole degree, the mode is 11 °C, occurring 6 times: Valley December (10.6), Aberporth November (10.8), and Ross-on-Wye February (10.8), March (10.6), November (11.4) and December (10.5). The next most common values are 9 °C, 10 °C and 19 °C, each 4 times.
The mode is weak here because temperature is a continuous measurement: the answer depends entirely on how much you round. Round to the nearest 5 °C and the mode becomes 10 °C; keep one decimal place and there is no mode at all. It is also telling you nothing useful — 11 °C is simply where late-autumn readings happen to cluster.
Across all 36 readings the mean is 14.7 °C (527.8 ÷ 36 = 14.6611) and the median is 14.1 °C, the average of the 18th and 19th values in the sorted list (13.5 and 14.7).
Meets criterion 3. This is the part most pupils get wrong: they invent a mode rather than saying the raw data has none, and they never state that the answer is an artefact of the rounding they chose.
Meets criterion 4: two vertical axes, each labelled with its quantity and unit and colour-matched to the data it carries, rainfall as bars on the left and temperature as a line on the right, with a caption naming the station, the year and the source.
Ross-on-Wye has by far the largest annual temperature range at 14.9 °C, compared with 11.9 °C at Valley and 11.5 °C at Aberporth — a difference of 3.0 °C and 3.4 °C. The gap comes almost entirely from summer: Ross-on-Wye averaged 21.8 °C in June to August against 19.5 °C at Valley, but in December to February the three stations were within 0.7 °C of each other (10.0, 9.8 and 9.3 °C). The sea heats up and cools down far more slowly than the land, so the two coastal stations are held back in summer and held up in winter, and their seasonal swing (9.7 °C and 9.6 °C) is about 2 °C smaller than the inland one (11.8 °C). That is continentality, and 60 km inland is enough to show it.
Rainfall works the other way round. Valley received 986.2 mm over the year and Aberporth 951.8 mm, but Ross-on-Wye only 829.4 mm — 156.8 mm less than Valley, or about 16 per cent less. The prevailing south-westerly winds arrive off the Irish Sea already full of moisture and are forced to rise over the Welsh uplands, so the rain falls on the coast and on the mountains; Ross-on-Wye sits east of the Black Mountains in their rain shadow, where the air is descending and drying. The warmest station is therefore also the driest, which is the opposite of what you might expect if you assumed warm air simply means more rain.
Meets criterion 5: six calculated figures are quoted, each attached to a claim, and both patterns are explained by distance from the sea and by relief rather than described.