The Pearson r Product Moment Coefficient of Correlation is the most common measure of correlation or association. The computation can be used for determining the relationship between two variables with paired observations. The r value can have possible values between -1 to +1. The closer the r value is to -/+ 1, the stronger is the relationship between the two variables. Consequently, as the r value approaches 0, the relationship gets weaker.
In the following example, Pearson r is used in order to determine the influence of the number of hospitals in a city to its maternal mortality rate (MMR).