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Science Forum Index » Statistics - Math Forum » T-test,Z-Test & F-Test & Chi-Square...
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| Judge... |
 Posted: Sun Jul 13, 2008 11:14 am |
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Guest
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All,
T-Test & Z-Test are used to check means of two groups. T-test is used
when groups are small & variance is not know otherwise Z-test is used
to check regarding mean diff. in two groups.
F-Test & Chi-Square are used to check variance of two groups. When
each of these is used.
I am not a statistics student but am a professional in OLAP reporting;
am trying to learn Data Mining(Stats) on my own. Your help in removing
my stat concepts confusions can save a lot of time for me. Thanks.
Judge |
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| Jack Tomsky... |
| Posted: Sun Jul 13, 2008 6:45 pm |
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Guest
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Quote: All,
T-Test & Z-Test are used to check means of two
groups. T-test is used
when groups are small & variance is not know
otherwise Z-test is used
to check regarding mean diff. in two groups.
F-Test & Chi-Square are used to check variance of two
groups. When
each of these is used.
I am not a statistics student but am a professional
in OLAP reporting;
am trying to learn Data Mining(Stats) on my own. Your
help in removing
my stat concepts confusions can save a lot of time
for me. Thanks.
Judge
Generally, you're right except that chi-square is used to test for a single variance. Suppose that the underlying distribution is normal with the mean and variance being unknown. We wish to test the null hypothesis H0: sig^2 = sig0^2, where sig^2 is the true population variance and sig0^2 is the specified population variance.
From the sample of size N, we calculate the sample standard deviation s. Then when H is true,
(N-1)s^2/sig0^2 has a chi-square distribution with N-1 degrees of freedom. We use this fact, along with whether the specified alternative hypothesis H1 is one-sided or two-sided to decide whether accept H0 or H1.
Jack |
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