Correlation means two things move together in a dataset. A proven cause needs more: evidence that removes the other explanations. This lesson shows how to tell the two apart and word your answer to match.
It is part of economic activity and environmental evidence. The next lesson, connecting an activity to an observed environmental change cautiously, builds on it.
How do I know a pattern is not yet a cause?
Ask whether something else could produce the same pattern. If the answer is yes, and the data cannot rule it out, you have a correlation.
A second test: could the pattern have been recorded even if the suspected cause did nothing? A single day of readings rarely answers that.
Worked example: a stream and a quarry
The numbers here are made up for illustration. A class is given water clarity readings from a stream. Clarity is measured as the depth in cm at which a marker disc disappears from view, so a bigger number means clearer water.
| Site | Distance below the quarry outlet | Clarity (cm) |
|---|---|---|
| A | 50 m | 12 |
| B | 200 m | 18 |
| C | 400 m | 25 |
| D | 800 m | 31 |
| E | 1 200 m | 38 |
| F | 1 600 m | 40 |
The pattern is clear. Clarity rises with distance from the quarry. The mean of the three nearest sites is (12 + 18 + 25) ÷ 3 = 18.3 cm, and the mean of the three furthest is (31 + 38 + 40) ÷ 3 = 36.3 cm, a gap of 18 cm.
The notes add one more fact: a bare slope beside sites A to C was cleared for building last month. Loose soil from that slope could also muddy the water at those same three sites. The data cannot separate the quarry from the slope.
The mistake that loses marks
A common slip is to write “The quarry reduces water clarity by 18 cm”. The figure is correct, but the verb claims a cause that the table has not shown.
| Level | Wording | Does the data allow it? |
|---|---|---|
| Pattern | The mean clarity is 18 cm lower at the three nearest sites | Yes |
| Link | Low clarity is linked to closeness to the quarry | Yes |
| Cause | The quarry reduces clarity | No, the cleared slope is a rival |
Use the highest level the evidence reaches, and stop there.
What evidence would turn the link into a cause?
Name the gap in the evidence, not just the word “more data”. Good choices for this stream are:
- A reading upstream of the quarry outlet, which the quarry cannot reach.
- Readings before the slope was cleared, to compare with now.
- Readings on more than one day, including after heavy rain.
- A process: sediment carried from settling ponds at the outlet.
A full answer might read: “Clarity rises from 12 cm at 50 m to 40 cm at 1 600 m, so low clarity is linked to closeness to the quarry. A cleared slope beside sites A to C is a second possible source, so a reading upstream of the outlet is needed before the quarry can be named as the cause.”
The graph evidence and fair-comparison lab helps you lay out rival explanations.
Check yourself
Five fictional coastal villages are compared. The village with the most fishing boats has the most plastic on its beach, and the ranking matches across all five. A student writes: “More boats cause more plastic.” Rewrite the sentence so the data support it, and name one extra piece of evidence.
Answer
A supported sentence: “Villages with more fishing boats also have more plastic on the beach, so the two are linked.” The data do not show that boats are the source.
Rival explanations include the village size, the amount of rubbish washed in by tides, and the number of visitors. One extra piece of evidence: the type of plastic found, for example net fragments and rope, which would point to boats, compared with food wrappers, which would point to visitors.
What to study next
Next, read connecting an activity to an observed environmental change cautiously, then write a full conclusion in writing a balanced geographical conclusion.
If you want a teacher to check how strongly your sentences claim a cause, see online one-to-one Geography tuition.