Overlapping area represents the amount of risk that can be diversified away by holding Visa Inc and Worldpay Inc in the same portfolio assuming nothing else is changed. The correlation between historical prices or returns on Worldpay and Visa is a relative statistical measure of the degree to which these equity instruments tend to move together. The correlation coefficient measures the extent to which returns on Visa are associated (or correlated) with Worldpay. Values of the correlation coefficient range from -1 to +1, where. The correlation of zero (0) is possible when the price movement of Worldpay has no effect on the direction of Visa i.e. Visa and Worldpay go up and down completely randomly.