The product-moment method, developed by Karl Pearson, is a statistical technique used to measure the linear correlation between two variables. It is based on the concept of the product moment, which is the sum of the products of the deviations of each pair of data points from their respective means. The product-moment correlation coefficient, denoted by r, is calculated by dividing the product moment by the product of the standard deviations of the two variables.
The product-moment method is a powerful tool for analyzing the relationship between two variables. It can be used to determine the strength and direction of the relationship, as well as the significance of the relationship. The product-moment method is also used to develop regression models, which can be used to predict the value of one variable based on the value of another.