Graziano and Raulin (8th ed)Graziano & Raulin
Research Methods (8th edition)

Computational Procedures
for Correlations

The appropriate correlation will depend on the level of measurement. If both variables produce score data, one should use the Pearson product-moment correlation. If one variable produces ordered data and the other variable produces either ordered or score data, one should use the Spearman rank-order correlation. If at least one variable is nominal, the appropriate correlation is Phi.

Pearson Product-Moment Correlation
Spearman Rank-Order Correlation