maths skills

Question 1

how do you calculate Spearman’s rank correlation coefficient?

Answer 1

1. state the null hypothesis
2. rank the data (separate ranks for each variable)
3. calculate the difference between the rank values for each pair of data
4. square the difference in rank values for each pair of data
5. find the sum of the differences squared, and find n
6. substitue these values into the equation to get r
7. check the significance of r using the corresponding critical value - if r is equal to or exceeds the critical value, the correlation is significant (reject the null hypothesis)

Question 2

how many pairs of measurements do you need to calculate Spearman’s rank correlation coefficient?

Answer 2

ideally at least 10 - if there are less this means the results will be highly insignificant and are more likely due to chance than a true correlation