Rank correlation

Command

Statistics Correlation Rank correlation

Description

When the distribution of variables is not Normal, the degree of relationship between the variables can be determined using Rank correlation. Instead of using the precise values of the variables, the data are ranked in order of size, and calculations are based on the differences between the ranks of corresponding values X and Y.

Required input

After selecting Rank correlation in the MedCalc menu, enter the names of the two variables in the following dialog box. For both variables, you can click the button to obtain a list of variables. In this list you can select a variable by clicking the variable's name. Optionally, you may also enter selection criteria in order to include only a selected subgroup of cases in the statistical analysis. Again, you can select the button to obtain a list of selection criteria already used for the current data.

MedCalc offers both Spearman's rank correlation coefficient rho and Kendall's tau.

Next click the OK button, or press the Enter key to obtain the following statistics in the results window:

Results

In this example the Spearman's coefficient of rank correlation rho is 0.114. The 95% confidence interval ranges from -0.084 to 0.304. The associated P-value is 0.255 and the conclusion therefore is that there is not a significant relationship between the two variables.

When you want to print these results, select the Print command in the Files menu, or press Ctrl+P.

Literature

• Armitage P, Berry G, Matthews JNS (2002) Statistical methods in medical research. 4th ed. Blackwell Science.
• Bland M (2000) An introduction to medical statistics, 3rd ed. Oxford: Oxford University Press.
• Altman DG (1991) Practical statistics for medical research. London: Chapman and Hall.

See also

• Correlation coefficient
• Scatter diagram
• Create correlation table for more than 2 variables

External links

• Rank correlation on Wikipedia.