Chapter 8: Bivariate correlational research

In this chapter we'll cover the following learning objectives:

1. Estimate results from a correlational study with two quantitative variables by looking at a scatterplot.

2. Understand how the correlation coefficient, r, represents strength and direction of a relationship between two quantitative variables.

3. Analyze a correlational study, in which at least one variable is categorical, by looking at a bar graph and computing the difference between the two means.

4. Interrogate the construct validity of an association claim, asking whether the measurement of each variable was reliable and valid.

5. Interrogate the statistical validity of an association claim, asking about features of the data that might distort the meaning of the correlation coefficient, such as outliers in the scatterplot, effect size, and the possibility of restricted range (for a lower-than-expected correlation). When the correlation coefficient is zero, inspect the scatterplot to see if the relationship is curvilinear.

6. Interrogate the external validity of an association claim by asking to whom the association can generalize.

7. Distinguish an association claim, which requires that a study meet only one of the three rules for causation (covariance), from a causal claim, which requires that the study also establish temporal precedence and internal validity.

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