Notice: On April 23, 2014, Statalist moved from an email list to a forum, based at statalist.org.
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: st: Interpretation of Two-sample t test with equal variances?
From
David Hoaglin <[email protected]>
To
[email protected]
Subject
Re: st: Interpretation of Two-sample t test with equal variances?
Date
Wed, 20 Mar 2013 12:43:50 -0400
Despite the tolerance of Student's t for departures from assumptions,
comparing the (mean) ages in the two outcome groups is not the right
approach. For initial exploration, side-by-side boxplots of age (by
mode_delivery) would give an indication of skewness, as well as
presence of unusually low or high ages. Apart from giving some points
undue influence, skewness in the distribution of a predictor (per se)
is often not important. If the predictor could be transformed, to
straighten a nonlinear relation with the outcome, the transformation
might (as a by-product) reduce or remove the skewness.
David Hoaglin
On Wed, Mar 20, 2013 at 12:16 PM, Gwinyai Masukume
<[email protected]> wrote:
> 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
*
* 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/