Wolfram Research
Wolfram Math World: Spearman Rank Correlation Coefficient
This page gives a description of the Spearman Rank Correlation Coefficient, which is an approximation to the exact correlation coefficient, r. It is somewhat easier to compute than the exact correlation coefficient. Also provides links...
Other
Correlation Coefficients
This page provides a good discussion of correlation coefficients (r,) which indicate the "strength of the linear association between variables." Includes formulas and scatter plots. Some prior knowledge of statistics might be helpful.
CK-12 Foundation
Ck 12: Plix Series: Correlation and Causation
[Free Registration/Login Required] Sort a list of events into a Venn diagram with the categories Causation and Correlation, then answer a challenge question.
Rice University
Hyper Stat Online Statistics Textbook: Correlation
This resource gives a definition of correlation and an example using a fire and fire fighters.