m38 problem set STATISTICS

Step 7

We can use Pearson’s r to calculate the association between two scale (interval or ratio) variables. The interpretation is the same as gamma. Here are the directions for using SPSS to calculate this statistic:

Pearson’s r

Analyze, Correlate, Bivariate

Highlight variable name, transfer to Variables field

Highlight 2nd variable name, transfer to Variables field

Pearson is the default choice, leave it that way.

Two-tailed is the default choice, leave it that way.

OK

Let’s try an example. Remember, we need to have 2 scale variables. Let’s pick respondents age (AGE) and number of brothers and sisters (SIBS). If you follow the directions above your screen should look like this:

Here is what your output will look like:

What does Pearson’s r tell us? It tells us that there is a perfect correlation (r = 1) when you compare age to age and sibs to sibs (that’s pretty obvious, right?). Now, let’s look at that other statistic: .061. What does that mean? There is a weak direct association between the two variables; that is, as age increases, the number of siblings tend to increase!