Fieldwork tables reward a short routine: find the pattern, calculate one or two summary figures, then deal with any reading that does not fit. This lesson walks through the routine with an original dataset.
It belongs to environmental management. For the skills of making a safe claim from such data, see explaining environmental impacts with evidence.
What is the routine?
- Read the title, units and the number of readings.
- Look for the highest, lowest and any reading that stands apart.
- Calculate the mean, median and range if the question needs them.
- Say what the pattern is, then what might explain it.
- State one limit of the data.
Work in that order, and each later step has something firm to rest on.
Worked example: litter on a beach
The numbers here are made up for illustration. A class counts litter items along a 10 m strip at six points on a fictional beach on one afternoon.
| Site | Items |
|---|---|
| 1 | 12 |
| 2 | 9 |
| 3 | 15 |
| 4 | 11 |
| 5 | 38 |
| 6 | 10 |
The field notes say Site 5 is beside a food stall. Start with the total: 12 + 9 + 15 + 11 + 38 + 10 = 95. The mean is 95 ÷ 6 = 15.8 items, to one decimal place.
For the median, put the readings in order: 9, 10, 11, 12, 15, 38. The middle two are 11 and 12, so the median is (11 + 12) ÷ 2 = 11.5. The range is 38 − 9 = 29.
The mean, 15.8, is higher than five of the six readings, because Site 5 pulls it upward. Without Site 5 the mean is (12 + 9 + 15 + 11 + 10) ÷ 5 = 57 ÷ 5 = 11.4, close to the median.
The mistake that loses marks
One slip is to quote only the mean and call the beach “moderately littered, at about 16 items per site”. Five of six sites are lower than that. Another slip is to drop Site 5 without saying so.
A stronger statement: “Five of the six sites had 9 to 15 items, with a median of 11.5. Site 5 had 38, more than three times the median, and it lies beside a food stall, which may explain it. The mean of 15.8 is raised by this one site, so the median better represents a typical site.”
| Weak | Strong |
|---|---|
| The mean is about 16. | The median of 11.5 represents a typical site because one site is unusual. |
| Site 5 is wrong, so I ignored it. | Site 5 is 38, beside a stall, and is kept and discussed. |
What limit should I state?
Choose a limit the data show. Here: six points on one afternoon cannot show whether Saturday or weekday counts differ, and the stall may empty its bin on a schedule. Practise summarising tables with the graph evidence and fair-comparison lab.
Check yourself
Original data: plastic bottle counts at five points along a fictional stream path are 4, 6, 5, 21 and 4. Find the mean and median, and say which better represents a typical point.
Answer
Mean = (4 + 6 + 5 + 21 + 4) ÷ 5 = 40 ÷ 5 = 8.
Ordered: 4, 4, 5, 6, 21, so the median is 5.
The median represents a typical point better, because one point with 21 pulls the mean above four of the five readings. The 21 should be kept, and the notes checked for a reason such as a nearby picnic area.
What to study next
Go on to separating local evidence from generic claims, then try the environmental management practice set.
To have a teacher go through your fieldwork tables and choose the right summary figure, see online one-to-one Geography tuition.