Correlation is a statistical measure that shows the extent to which two or more variables vary together. There are two types of correlations:

- A positive correlation ranges between 0 and +1. It indicates that the dependent and independent variable increase or decrease corresponding to each other. So basically, a strong positive correlation means that, as the age of a person increases, the blood pressure will increase with it. The correlation for such a relationship will be closer to 1.
- A negative correlation ranges between -1 and 0. It shows the extent to which one variable increases as the other decreases. A strong negative correlation suggests that the as the age of a person increases, the blood pressure decreases and vice versa, in which case, the correlation between the age and blood pressure will be closer to -1.