Possible Clues:

• In statistics, a ____ coefficient is the covariance of the random variables X and Y, divided by the square root of the product of their variances
• Mutual connection in gracious story
• Link goodness and joy? That's about right
• Statistical interdependence
• Interdependence or the degree of it
• Interdependence
• Interdependence (of statistical variables)
• & 24 Eclair of confectioner? It belies a certain dependency
• Mutual relationship of interdependence