Thursday, November 26, 2009

Paired t-test

I always forget what P value must be to reject or not to reject null hypothesis in paired t-test. So lets explain by the example.

H0 - null hypothesis - there is no
significant difference
between method A and B
H1 - alternative hypothesis - there is difference
(two tail test)

For example [with 5% (a=0.05) level of significance ]:

Based on the above results I can say that: since P=0.009103483 and this is lover than a=0.05 (P<0.05), I can claim that:

I'm 95% (a=0.05) sure that there is significant
difference between A and B, because (P<0.05).


On the other hand, we can have:

In this case P=0.649507752, hence I can claim that:

I'm 95% (a=0.05) sure that there is no significant
difference between A and B, because (P>0.05).

Above paired t-test was performed in Excel.

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