Correlations
Psychology: AQA A Level, topic 7.1.5
Correlation
Correlation means that there is a relationship between two or more variables (such as ice cream consumption and crime). But this relationship does not necessarily imply cause and effect.
Correlation
- When two variables are correlated, it simply means that as one variable changes, so does the other.
- We can measure correlation by calculating a statistic known as a correlation coefficient.
- A correlation coefficient (usually represented by the letter r) is a number from -1 to +1 that indicates the strength and direction of the relationship between variables.
The correlation coefficient
- The number portion of the correlation coefficient indicates the strength of the relationship.
- The closer the number is to one (be it negative or positive), the more strongly related the variables are, and the more predictable changes in one variable will be as the other variable changes.
- The closer the number is to zero, the weaker the relationship, and the less predictable the relationships between the variables becomes.
Sign of the correlation coefficient
- The sign- positive or negative - of the correlation coefficient indicates the direction of the relationship.
- A positive correlation means that the variables move in the same direction, or as one variable increases/decreases so does the other.
- A negative correlation means that the variables move in opposite directions, so a decrease in one variable is associated with an increase in the other and vice versa.
Correlational research
- Correlational research is useful because it allows us to discover the strength and direction of relationships that exist between two variables.
- But correlation is limited because establishing the existence of a relationship tells us little about cause and effect.
Cause-and-effect relationships
- While variables are sometimes correlated because one does cause the other, it could also be that some other factor, a confounding variable, is actually causing the movement.
- Even when we cannot point to clear confounding variables, we should not assume that a correlation between two variables implies that one variable causes changes in another.
- This can be frustrating when a cause-and-effect relationship seems clear and intuitive.
- Unfortunately, people mistakenly make claims of causation as a function of correlations all the time.
Test yourself on Correlations
What is a correlation?