Spearman’s rank correlation coefficient
In Chapter 4, Parametric Tests, we looked at the parametric correlation coefficient, Pearson’s correlation, where the coefficient is calculated from independently sampled, continuous data. However, when we have ranked, ordinal data, such as that from a satisfaction survey, we would not want to use Pearson’s correlation as it cannot be assumed to guarantee the preservation of order. As with Pearson’s correlation coefficient, Spearman’s correlation coefficient results in a coefficient, r, that ranges from -1 to 1, with -1 being a strong inverse correlation and 1 being a strong direct correlation. Spearman’s is derived by dividing the covariance of the two variables’ ranks by the product of their standard deviations. The equation for the correlation coefficient, r, is as follows:
r s = S xy _ √ _ S xx S yy
Where
S xy =...
