Microsoft Office Tutorials and References

In Depth Information

Fig. 6.8
Worksheet for Computing the Correlation, r

Notice that when Excel multiplies a minus number by a minus number, the result

is a plus number (for example for student #7: (

0.29.

And when Excel multiplies a minus number by a plus number, the result is a

negative number (for example for student #1: (

0.46) x (

0.64)

¼þ

─

─

0.06) x (

þ

0.16)

¼
─

0.01 .

─

Note:
Excel computes all computation to 16 decimal places. So, when you check

your work with a calculator, you frequently get a slightly different answer than

Excel’s answer.

For example, when you compute above:

X

Y

ð

X

Þ

x

ð

Y

Þ

for student #2

your calculator gives :

(6.2)

;

(

0.0216

As you can see from the table, Excel’s answer is

0.36) x (

þ

0.06)

¼
─

─

0.02 which is really
more

accurate
because Excel uses 16 decimal places for every number, even though only

two decimal places are shown in Figure
6.8
.

You should also note that when you do Step 6, you have to be careful to add all of

the positive numbers ﬁrst to get

─

þ

1.10
and then add all of the negative numbers

1.07

as your answer to Step 6. When you do these computations using Excel, this total

ﬁgure will be

0.03
, so that when you subtract these two numbers you get

þ

second to get

─

1.09
because Excel carries every number and computation out to 16

decimal places which is much more accurate than your calculator.

þ

7. Multiply the answer for step 2 above by the answer for step 6

(0.14286 x 1.09)

0.1557

8. Multiply the STDEV of X times the STDEV of Y (0.48 x 0.39)

0.1872

9. Finally, divide the answer from step 7 by the answer from

step 8 (0.1557 divided by 0.1872)

þ

0.83

This number of
0.83
is the correlation between HSGPA (X) and FRGPA (Y) for

these 8 students. The number

þ

0.83
means that

there is a strong, positive

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