Data can show a positive correlation, a negative correlation or none. Before concluding that one variable causes another, think about other explanations. Two variables might both be caused by a third factor, or the link might be due to chance in a small sample.
Scientists strengthen conclusions with large samples, control groups, repeat studies and a plausible mechanism, a scientific reason why one factor should affect the other. For example, the link between smoking and lung cancer was accepted because many large studies agreed and scientists found how chemicals in smoke damage cells.
Worked example
In a town, more ice-cream sales are linked with more drownings. Does ice cream cause drowning?
- Both rise in hot weather.
- Hot weather leads to more swimming and more ice cream.
Answer:No: a third factor, temperature, explains both.
Key words
- causal link
- one factor directly causes another
- mechanism
- a scientific explanation of how a cause works
- sample size
- the number of individuals or measurements
- control group
- a group that does not get the treatment
New questions every time.