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Re: st: Interpretation of Two-sample t test with equal variances?


From   Richard Williams <richardwilliams.ndu@gmail.com>
To   statalist@hsphsun2.harvard.edu, statalist <statalist@hsphsun2.harvard.edu>
Subject   Re: st: Interpretation of Two-sample t test with equal variances?
Date   Wed, 20 Mar 2013 00:41:50 -0500

Your t-test seems to suggest that age is affected by mode of delivery, rather than mode of delivery is affected by age. It probably won't change things much but this makes more sense to me given your hypotheses:

logit mode_delivery age

At 11:08 PM 3/19/2013, Gwinyai Masukume wrote:
Dear Stata list,

I would like to double check the interpretation and appropriateness of
the following statistical test I performed.
My alternate hypothesis is that, ?There is a difference in the baby?s
mode of delivery depending on maternal age? And the null hypothesis is
that, ?There is no difference in the baby?s mode of delivery depending
on maternal age?
Looking at the output ­ ?Ha: diff != 0, Pr(|T| > |t|) = 0.4861?, I
fail to reject the null hypothesis and conclude that, ?There is no
difference in the baby?s mode of delivery depending on maternal age?

Is this a sound and appropriate interpretation?

. *** Doing a T-test
. ttest age, by(mode_delivery)

Two-sample t test with equal variances
------------------------------------------------------------------------------
Group | Obs Mean Std. Err. Std. Dev. [95% Conf. Interval]
---------+--------------------------------------------------------------------
Vaginal | 166 28.83072 .4696729 6.051313 27.90338 29.75807
C/sectio |      84    29.39524    .6579862    6.030543    28.08653    30.70395
---------+--------------------------------------------------------------------
combined |     250     29.0204    .3818851    6.038134    28.26826    29.77254
---------+--------------------------------------------------------------------
diff | -.5645152 .8093331 -2.158558 1.029528
------------------------------------------------------------------------------
diff = mean(Vaginal) - mean(C/sectio) t = -0.6975
Ho: diff = 0                                     degrees of freedom =      248

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
Pr(T < t) = 0.2431 Pr(|T| > |t|) = 0.4861 Pr(T > t) = 0.7569

With kind regards,
Gwinyai

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Richard Williams, Notre Dame Dept of Sociology
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