Linear regression is used to predict the value of one variable from another variable. Since it is based on correlation, it cannot provide causation. In addition, the strength of the relationship between the two variables affects the ability to predict one variable from the other variable; that is, the stronger the relationship between the two variables, the better the ability to do prediction. For example, given this data on literacy and undernourishment, we can seea scatter plot which shows that there seems to be a relationship between the variables.