"alternate t-test" following sig Levene's test

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boothswa
Posts: 3
Joined: Wed Aug 22, 2012 6:27 pm

"alternate t-test" following sig Levene's test

Postby boothswa » Thu Aug 23, 2012 6:19 pm

What exactly is the "alternate test"? What is SPSS doing? Why reduced d.f., etc? In short, what is going on?

If I use this test, I have to be able to describe it somehow. I cant just say "SPSS manual said to use the "alternate test".

Thanks much,
Penguin_Knight
Posts: 473
Joined: Thu Apr 05, 2012 5:58 pm

Re: "alternate t-test" following sig Levene's test

Postby Penguin_Knight » Thu Aug 23, 2012 8:20 pm

Levene's test appears in a few places in SPSS, which analytical function are your referring to?
boothswa
Posts: 3
Joined: Wed Aug 22, 2012 6:27 pm

Re: "alternate t-test" following sig Levene's test

Postby boothswa » Thu Aug 23, 2012 9:44 pm

In the t-test procedure. If Levene's F is significant (i.e. null hypothesis that data is not homogenous is rejected), then spss provides an "alternate t-test" rather than the "normal" t-test. d.f. that are presented sometimes differ in the alt test compared to the normal test, as does p.

Thanks for your help
Penguin_Knight
Posts: 473
Joined: Thu Apr 05, 2012 5:58 pm

Re: "alternate t-test" following sig Levene's test

Postby Penguin_Knight » Sat Aug 25, 2012 6:35 pm

In the same table, if Levene's test is not significant (p >= 0.05), read the first line of the t-test portion. If the Levene's test is significant (p < 0.05), read the second line of the t-test portion.

The two lines differs in how the variance is estimated. If the two distributions are the same, then the variance is pooled, if the two are different, then the variance would be a combination of two sets of variance. For the formula, you can see here:
http://www.okstate.edu/ag/agedcm4h/acad ... page26.htm
boothswa
Posts: 3
Joined: Wed Aug 22, 2012 6:27 pm

Re: "alternate t-test" following sig Levene's test

Postby boothswa » Sat Aug 25, 2012 8:01 pm

thank you!!

I could not find that info anywhere....so also thanks for getting me to the OK.edu site (for potential other answers)

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