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R: st: Interpretation of Two-sample t test with equal variances?
From
"Carlo Lazzaro" <[email protected]>
To
<[email protected]>
Subject
R: st: Interpretation of Two-sample t test with equal variances?
Date
Wed, 20 Mar 2013 15:48:42 +0100
Gwinyai,
your Pseudo R2 = 0.0015 seems very low.
Are you sure that all the relevant independent variables have been included
in your model?
You may also consider searching for interactions between mode_delivery &
age.
Best regards,
Carlo
-----Messaggio originale-----
Da: [email protected]
[mailto:[email protected]] Per conto di Gwinyai Masukume
Inviato: mercoledì 20 marzo 2013 06:05
A: [email protected]
Oggetto: Re: st: Interpretation of Two-sample t test with equal variances?
Thank you Richard. Yes, I guess the t-test suggests the counter intuitive
though it probably won?t change things much.
How can I reverse the situation?
I ran a logistic regression for binary outcomes as you suggested:
Essentially no significance is shown?
. logit mode_delivery age
Iteration 0: log likelihood = -159.58665
Iteration 1: log likelihood = -159.34203
Iteration 2: log likelihood = -159.34197
Iteration 3: log likelihood = -159.34197
Logistic regression Number of obs =
250
LR chi2(1) =
0.49
Prob > chi2 =
0.4842
Log likelihood = -159.34197 Pseudo R2 =
0.0015
----------------------------------------------------------------------------
---
mode_delivery | Coef. Std. Err. z P>|z| [95% Conf.
Interval]
--------------+---------------------------------------------------------
--------------+-------
age | .0155454 .0222368 0.70 0.485 -.028038
.0591288
_cons | -1.133737 .6630978 -1.71 0.087 -2.433385
.1659111
----------------------------------------------------------------------------
---
With thanks,
Gwinyai
On 3/20/13, Richard Williams <[email protected]> wrote:
> 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
>>
>>*
>>* For searches and help try:
>>* http://www.stata.com/help.cgi?search
>>* http://www.stata.com/support/faqs/resources/statalist-faq/
>>* http://www.ats.ucla.edu/stat/stata/
>
> -------------------------------------------
> Richard Williams, Notre Dame Dept of Sociology
> OFFICE: (574)631-6668, (574)631-6463
> HOME: (574)289-5227
> EMAIL: [email protected]
> WWW: http://www.nd.edu/~rwilliam
>
>
> *
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> * http://www.ats.ucla.edu/stat/stata/
>
*
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