Correlations & Causal Relationships - The Lungs (AQA A Level Biology): Revision Note
Exam code: 7402
Correlations & causal relationships
Correlation
A correlation is an association between variables, e.g.:
positive correlation: as variable A increases, variable B increases
negative correlation: as variable A increases, variable B decreases
A correlation coefficient can be calculated to determine the strength of a correlation
Causal relationships
Causation, or a causal relationship, is present when a change in one variable is caused by a change in the other
Correlation does not equal causation
The two variables may be linked by a third factor that has not been taken into account by the research
In order to demonstrate that a correlation indicates a causal relationship, researchers need to:
see the same results repeated across many studies
demonstrate that the causal factor is occurring before the resulting change
demonstrate the causal mechanism
carry out controlled trials (this is not always possible)
Examiner Tips and Tricks
When drawing conclusions from data in exams, you should always be careful not to go beyond what the data show.
For example, if a graph shows a positive correlation between pollution levels and COPD, it would be correct to say that:
there is an association between the two
increasing pollution levels are correlated with an increase in COPD / there is a positive correlation
It would not be correct to claim that the increase in one causes the other to increase; more data would be needed before reaching this conclusion.
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