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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