Understanding research: the direction of a correlation

As mentioned in my last blog in the Understanding Research Series, correlations have a direction. So what does this mean?

Positive Correlations

Negative Correlations

Positive correlations

Say you are looking at two factors which are correlated like the the grades students achieve and the amount of studying they do.

Some research found the following:
Unsurprisingly the fewer hours a student spent studying the lower their final grades are likely to be and conversely the more hours they spend studying the higher their grades are likely to be.

This means that as one variable (the amount of hours spent studying) increases so does the other variable. And conversely as the number of hours decreases so does the grade level the student is likely to achieve. This is called a positive correlation. Basically this says that the direction of the correlation are tied together, they move in the same direction; as one goes up so does the other.

 

 

Negative Correlations
A negative correlation says the opposite. As one variable increases and other decreases. For example we could look at the grade a student gets compared to the number of beers they drink. What we are likely to find here is that the more a student drinks just before an exam the lower their grade is going to be. So the student who drinks just one beer before the exam is very likely to get better grades than the students who drink 15 beers before the exam!

This is a negative correlation. So the direction of the relationship between the two things are opposite, as one increases the other decreases.

The direction of a correlation is important because it tells you about the nature of their relationship.

In the next blog in this series I will take this a little further and look at the idea of the perfect correlation or the perfect relationships, strong relationships and weak relationships and what they mean.