Correlation

The degree of association or strength of relationship between two variable is represented by a number called a correlation coefficient. The person product moment correlation coefficient is a measure of the linear relationship between two variable X and Y, and is denoted by r_{xy} or simply r, The population correlation coefficient is denoted by the Greek letter r(rho).

The value of a correlation coefficient can range from -1 to 1. A value of +1 denotes a perfect positive relationship. All the data points fall on straight line such that high scores on one variable are paired with high scores on the other, and low scores are paired with low scores.

A coefficient of -1 denotes a perfect negative or inverse relationship. For this case all the data points on a straight line such that high scores on one variable are paired with high scores on the other, and low scores are paired with low scores.

A coefficient of -1 denotes a perfect negative or inverse relationship. For this case, the data points also fall on a straight line,but high scores on one variable are paired with low scores on the other and vice versa resulting in a line that slopes down instead of up, If these is no linear association between the variables, r is equal to 0. In this case the data points tend to fall in a circle.

Intermediate degree of association are represented by coefficient less then 0 (-1<r<0)  or by coefficient greater then 0 (0<r<1).

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