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Re: st: Interpretation of Two-sample t test with equal variances?
From
Gwinyai Masukume <[email protected]>
To
[email protected]
Subject
Re: st: Interpretation of Two-sample t test with equal variances?
Date
Wed, 20 Mar 2013 18:16:26 +0200
Thank you so much everyone. Appreciated.
David - it was indeed a very helpful discussion.
Nick - indeed those are means of maternal age. you are significant.
yes, the mother's ages are skewed. what do you mean by student's t
test works well even if you lie to it?
Carlo - it seems all the relevant independent variables have not been
included, the very low pseudo r2 is bizarre to me.
Thanks again.
Gwinyai
On 3/20/13, Carlo Lazzaro <[email protected]> wrote:
> 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
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>>>* 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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>>
>
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