Correlation
A A relationship between two sets of data, such that when one set changes you would expect the other set to change as well. shows a connection between a factor and an outcome.
To describe a correlation in words state:
- the change in the factor
- how the outcome changes as this happens
- how the pattern of change in each factor is similar or different
Here is an example, with each marking point shown as [1]:
'As carbon dioxide levels increase [1], the global average temperature increases [1] and the increases follow a similar pattern [1].'
Correlations in tables
To spot correlations in data, look at how the numbers change in each column of the data table.
| Factor | Outcome |
| As the values of the data here increase... | ...the values of the data here increase in a similar way |
| Factor | As the values of the data here increase... |
|---|---|
| Outcome | ...the values of the data here increase in a similar way |
| Factor | |
|---|---|
| Outcome |
| Factor | |
|---|---|
| Outcome |
The trend in the outcome is the same as the factor.
| Factor | Outcome |
| As the values in the data here increase... | ...the values of the data here decrease in an opposite way |
| Factor | As the values in the data here increase... |
|---|---|
| Outcome | ...the values of the data here decrease in an opposite way |
| Factor | |
|---|---|
| Outcome |
| Factor | |
|---|---|
| Outcome |
The trend in the outcome is the opposite of the trend in the factor.
Data which does not show a correlation has no similar or opposite trend in the outcome.
| Factor | Outcome |
| As the values in the data here increase... | ...the values of the data here go up, down or do not change |
| Factor | As the values in the data here increase... |
|---|---|
| Outcome | ...the values of the data here go up, down or do not change |
| Factor | |
|---|---|
| Outcome |
| Factor | |
|---|---|
| Outcome |
The upwards trend is the factor not present in the outcome.
Correlations in graphs
Graphs can also reveal correlations.
This graph shows increasing carbon dioxide levels in the atmosphere.
This graph shows a similar increase in global average temperature.
It is important that the graphs show similar trends. This is most easily seen if graphs are overlaid on top of each other.