Spearman's rangcorrelatietest

Spearman's rank correlation is a nonparametric test used to find the association between two variables in paired data.

Consider an example of finding a correlation between the eggshell thickness and the hatching order for 35 turtle eggs.

Here, the hatching order cannot be measured parametrically. Instead, it can only be ranked based on its order. Similarly, the eggshell thickness can be ranked in increasing order of thickness measured after hatching.

To conduct the test, we begin with the null hypothesis that there is no correlation between the two variables and the alternative hypothesis that a correlation exists between them.

The quantity Rho-sub-S or Spearman's rank correlation coefficient is a population parameter estimated from the sample statistic R-sub-S using the following equation.

The sample size is more than 30, so the critical value is calculated using the following equation.

Notice the sample statistic is beyond the threshold of the critical value, suggesting that there is a correlation between eggshell thickness and hatching order.