Microsoft Office Tutorials and References
In Depth Information
Comparing Results to an Estimate
Comparing Results to an Estimate
The Chi Square test is a statistical method for determining whether observed
results are within an acceptable range compared with what the results were
expected to be. In other words, the Chi Square is a test of how well a before
and after compare. Did the observed results come close enough to the
expected results that we can safely assume there is no real difference? Or
were the observed and expected results far enough apart that we must
conclude there is a real difference?
A good example is flipping a coin 100 times. The expected outcome is 50
times heads, 50 times tails. Figure 10-2 shows how a Chi Square test statistic
is calculated in a worksheet without using any functions.
Figure 10-2:
Calculating
a Chi
Square.
Cells B5:B6 are the expected results — that heads and tails will each show
up 50 times. Cells C5:C6 show the observed results. Heads appeared 44
times, and tails appeared 56 times. With this information, here is how the Chi
Square test statistic is calculated:
1.Foreachexpectedandobservedpair,calculatethedifferenceas
(Expected Observed ).
2.Calculatethesquareofeachdifferenceas (Expected Observed ) 2 .
3.Dividethesquaresfromthepreviousstepbytheirrespective
expectedvalues.
4. Sum the results of the previous step.
Of course, a comprehensive equation can be used for the first three steps,
such as =(expected - observed)^2/expected.
The result in this example is 1.44. This number — the Chi Square value — is
then looked up in a table of Chi Square distribution values. This table is a
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