Microsoft Office Tutorials and References

In Depth Information

In order to help you to understand where the correlation number that ranges

from -1.0 to +1.0 comes from, we will walk you through the steps involved to use

the formula as if you were using a pocket calculator. This is the one time in this

book that we will ask you to use your pocket calculator to ﬁnd a correlation, but

knowing how the correlation is computed step-by-step will give you the

opportunity to understand how the formula works in practice.

To do that, let’s create a situation in which you need to ﬁnd the correlation

between two variables.

Suppose that you wanted to ﬁnd out if there was a relationship between high

school grade-point average (HSGPA) and freshman GPA (FRGPA) for Biology

majors at a College of Science and Technology. You have decided to call HSGPA

the x-variable (i.e., the predictor variable) and FRGPA as the y-variable (i.e., the

criterion variable) in your analysis. To test your Excel skills, you take a random

sample of freshmen Biology majors at the end of their freshman year and record

their GPA. The hypothetical data for eight students appear in Fig.
6.7
. (Note: We

are using only one decimal place for these GPAs in this example to simplify the

mathematical computations).

Fig. 6.7 Worksheet data for

high school GPA and frosh

GPA (practical example)

Notice also that we have used Excel to ﬁnd the sample size for both variables, X

and Y, and the MEAN and STDEV of both variables. (You can practice your Excel

skills by seeing if you get these same results when you create an Excel spreadsheet

for these data).

Now, let’s use the above table to compute the correlation r between HSGPA

and FRGPA using your pocket calculator.

Search JabSto ::

Custom Search