Microsoft Office Tutorials and References

In Depth Information

Fig. 6.7
Worksheet Data for High School GPA and Frosh GPA (Practical Example)

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.)

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 this 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.

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