The Correlational Study

The correlation between outside temperature and residential electric bills

The relationship between high school ACT scores and college freshman GPAs

The correlation between upper arm strength and push up performance

Correlations show both direction (positive or negative) and strength (how positive or negative). Coefficients range from high positive, where both variables increase or decrease at the same time (with +1.00 being perfect) to high negative, where one variable increases as the other decreases (with -1.00 being perfect). No relationship is 0.00.

The Pearson's r or Spearman Rho are commonly used to show the extent to which the relationship exists. The scatter plot, or scattergram, gives a graphic display of the pattern of the association between the two variables. For more on scatter plots, see All Psych: Correlation

When writing research reports that involve correlations, avoid words that are causal in nature. Using the sample study above, it would be incorrect to state that high school ACT performance affected college GPA, since it is a noncausal relationship. A phrase such as associated with gives a more accurate description of the relationship.

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