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: (-0.46) 9 (-0.64) = +0.29.

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

negative number (for example for student #1: (-0.06) 9 (+0.16) =-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
X

Þ
Y
Y

ð

ð

Þ
for student #2
;
your calculator gives :

0
:
36

ð
6
:
2
Þ

ð

Þ
0
:
06

ð

Þ¼
0
:
0216

As you can see from the table, Excel’s answer is -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 Fig.
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 +1.10 and then add all of the negative numbers

second to get -0.03, so that when you subtract these two numbers you get +1.07 as

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

ﬁgure will be +1.09 because Excel carries every number and computation out to

16 decimal places which is much more accurate than your calculator.

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