Re: T test


: I did a t test to compare whether there is any significant
:difference between two treatments or not? The SPSS output says that
:there is a difference between the two treatments.

Right.

: But when i go for the 95% confidence interval for the two
:treatments individually it was concluded that there is no significant
:difference. Beacuse the two confidence intervals are overlapping.

The individual (two) CI's may overlap andstill the difference is
regarded as significant because you must use the sampling distribution
of difference of means (standard error of difference) not individual
standard error of means as such a simple way.

:the t value =-2.446
:p value=0.040
:mean difference=-1.6258
:standard error of difference=0.66458

There is a small risk p=.040 that these two samples are drawn from the
same population, thus we discard the Ho and accept the two-tailed
alternative H1 that there is a true difference.

Cheers Erkki

040-5024491 <http://www.helsinki.fi/people/Erkki.Komulainen/>
.

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