# Test for Equal Mean

Six Sigma – iSixSigma Forums Old Forums General Test for Equal Mean

Viewing 9 posts - 1 through 9 (of 9 total)
• Author
Posts
• #27794

wei
Member

I want to perform a test of equal mean (t-test) to three incoming lots from vendor. I know that I can use Two-Sample T-Test for test equivelency for two lots, then what about three lots? Is there a particular test for three lots? Thanks!

0
#68512

Ken Myers
Participant

Wei,
To compare more than two means you could use a statistical test called Analysis of Variance or ANOVA.  It’s a very standard test and is explained in most stat texts, as well as supported by most stat software.
Good luck,
Ken

0
#68515

DEVASHISH DEY
Participant

You can also use paired t-test

0
#68516

Riaz Rasul
Member

Hi,
You can do this by ANOVA. This will basically compare multiple number of means.
Thanks
Riaz

0
#68536

Member

Use Analysis of variance

0
#68538

Ken Myers
Participant

A paired t-test looks at differences between TWO groups subjected to the same treatment.  This test is not appropiate for more than TWO groups.

0
#68552

Thom
Member

Ken is absolutely correct.  If you used paired comparisons for all possible comparisons, you really hurt yourself for your Type I error rate.  Use ANOVA, but be cognizant of the assumptions.  If these do not pan out, consider the nonparametric alternatives (like Kruskall-Wallace).
Now, some folks struggle with the results from the ANOVA.  Okay, I have concluded that there is a significant difference between treatment means.  Where are these differences?  To answer this, you then utilize multiple comparisons.  There are quite a few to chose from, and you have to understand what you are actually looking for in relation to your Types I and II errors.  These include Tukey, Bonferonni, Scheffe, Duncan’s Multiple Range Test, Student-Newman-Keuls (SNK).
BUT, with any test/procedure, know what you are testing for, understand the assumptions associated with the test/procedure, understand what diagnostics you have to make (as well as remedial actions).

0
#68556

Tommy
Member

Test the variances between the three as an indication of process stability for each supplier, I think this is now called a test for equal variances in MiniTab.

0
#68567

kbower50
Participant

You’re right – it used to be called the homogeneity of variance test, but was changed to “test for equal variance” due to customer demand.  I’ve a paper on using MINITAB to do ANOVA, along with relevant references, reproduced from SC&I at http://www.minitab.com/company/VirtualPressRoom/Articles/SCIFeb2000ANOVA.htm
Hope it helps.  There’s also a paper on the paired t-test through http://www.minitab.com/company/virtualpressroom/Articles/index.htm

0
Viewing 9 posts - 1 through 9 (of 9 total)

The forum ‘General’ is closed to new topics and replies.