As you examine the relationship between any two variables, here are some key points to keep in mind:
- Do the two variables move in the same direction as one changes, or do they move in opposite directions? Is there one critical value in either of the variables that alters the relationship?
- Are the changes in the values dramatic, or are they slow and steady?
- Is there strength in the relationship, and is the relationship linear, or is there curvature?
- Are there specific subsets of data that have correlations that are more interesting than others?
The kinds of plots and charts one uses to display these relationships are dependent upon the variable data types. For interval and ratio scale ...