September 6 is a day where we just check the
assignment that we have. But as we check, we are not only after the high points
but we are also after the principle or idea behind. Our assignment is about
testing the difference between two variances. There are ideas that we always
should remember. These are the following:
1.
When
finding the critical value for one-tailed test, we just have to know the level
of significance, the d.f.N which is obtain by subtracting 1 to the number of
sample or n and the d.f.D which is also obtain by subtracting 1 from the n. And
finallly, you just need to find the intersection between the d.f.N and the
d.f.D.
2.
If it is a
two tailed test, we should first split the alpha, and then obtain the d.f.N and
d.f.D. Then find the intersection between them.
3.
We should
always remember that the larger the variance should be the s21
and placed in the numerator of the formula. In identifying the s21,
we should be after the bigger variance not the bigger number of sample.
4.
When
P-value method is use, it requires looking through all the F tables using the
specific d.f.N and d.f.D values.
Let
me give you an example of the problem that we have answered that day.
·
A manager
hypothesize that the variance for the number who buys female footwear is
greater than the variance for the number who buys male footwear. The data are
shown below. Is their enough evidence to support the claim using a=0.01?
Male Female
n= 23 n=
19
s21=3.8 s22=
4.6
1.
State the
hypothesis
H0: δ21
≤ δ22
H1: δ21 >
δ22
2.
Find the
critical value.
d.f.N=18, d.f.D= 22, C.V= 2.98
3.
Solve for the F-Test
F=
s21/ s22
F= 4.6/3.8= 1.21
4. Make the decision
Do not reject the null hypothesis since 1.21
< 2.98
5. Summarize the results
There is not enough
evidence to support the claim
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