When we want to know if there is relationship between two or more variables, we need to calculate their covariance or correlation indexes. These to will show us how much two variables are related together. If these indexes have greater values (in correlation, near to 1), then showing us there is straight relation between variables. And if their values be huge negative number (in correlation, near to -1) then it showing the inverse relation between variables. However, if value of these indexes be near to 0, then it suggesting no relation between variables.