Re: st: wsanova syntax

[Christian Genova <cagenova@avrdc.org>]

Thanks for the immediate response. The time element in my dataset is 3 
and not 2 as previously mentioned. ID is nested under control. I 
mistakenly placed "id" before "control" but yes, id #1 under control 1 
is different from id #1 in control 2.

With these, the syntax I used then is correct?

I initially used the non-parametric tests (Wilcoxon signed rank and 
Mann-Whitney U rank tests) but decided to use WSANOVA at the end. In the 
research I'm doing where weights and heights of children cannot really 
be uniform, the samples are expected to be non-homogenous. I'm not a 
statistician so I'm open to any suggestions to make my study more 
reliable and accurate though.

Joseph Coveney wrote:

> Christian Genova wrote:
>
> Can someone kindly lend assistance on the wsanova syntax for repeated
> measures. I'm still a novice with STATA so hope anyone can assist.
>
> There are 2 repeated variables: id and control.  ID is person belonging
> to group "control".  Tthe same persons in year 1 (id) belonging to group
> (control) were analyzed in time 2.
> I want to compare the scores in time 1 and 2, between time (scores in
> time 1 compared with scores in time 2) and control in time 1 and 2
> (whether there was signicant difference in scores of "control 1" at time
> 1 to scores at time 2, and within "control" in time 1 and 2 (whether
> there was significant difference between scores of "control 1 and 2" in
> time 1 compared to time 2).
>
> time      id    control    score
> ----------------------------------
> 1         1      1            5
> 1         2      1            6
> 1         3      1            5
> 1         1      2            3
> 1         2      2            4
> 2         1      1            7
> 2         2      1            8
> 2         3      1            5
> 2         1      2            2
> 2         2      2            10
>
> I used:   wsanova  SCORE CONTROL, id(ID) between(TIME).  Is this correct?
>
> --------------------------------------------------------------------------------
>
> The syntax for -wsanova- doesn't look right.
>
> >From your description, I'm assuming that id is nested under control, that
> is, that id #1 under control #1 is not the same person as id #1 under
> control #2.  If that's the case, then the syntax for -wsanova- would look
> more like that below for your setup.  (Note that -repeated()- or -epsilon-
> is superfluous with only two levels of the time factor.)
>
> Keep in mind that what you've displayed is an unbalanced dataset.  And that
> some of the of contrasts you're after (if I followed your description
> correctly) would involve Satterthwaite weighting of between and within
> variances.
>
> Have you considered forgoing ANOVA and just use Student's t-test  for the
> specific comparisons of interest?
>
> Type -help ttest- for syntax for paired and independent samples.
> Alternatives could be the Mann-Whitney U / Wilcoxon rank-sum (-ranksum-) and
> Wilcoxon sign-rank(-signrank-) tests.
>
> Joseph Coveney
>
> clear
> set more off
> input time      id    control    score
> 1         1      1            5
> 1         2      1            6
> 1         3      1            5
> 1         1      2            3
> 1         2      2            4
> 2         1      1            7
> 2         2      1            8
> 2         3      1            5
> 2         1      2            2
> 2         2      2            10
> end
> compress
> replace id = control * 10 + id
> order control id time
> sort control id time
> list, noobs sepby(control)
> anova score control / id|control time time*control, repeated(time)
> wsanova score time, id(id) between(control) epsilon
> exit
>
>
> *
> *   For searches and help try:
> *   http://www.stata.com/support/faqs/res/findit.html
> *   http://www.stata.com/support/statalist/faq
> *   http://www.ats.ucla.edu/stat/stata/
>
>
>
>   
--
---------------------------------------------------------------
Christian A. Genova II
Research Assistant
Socio-Economics Unit II
AVRDC – The World Vegetable Center
P.O. Box 42, Shanhua
74151 Tainan, TAIWAN, R.O.C.
Tel +886 6 583 7801 ext 462
Fax +886 6 583 0009
Email: cagenova@avrdc.org
www.avrdc.org
--------------------------------------------------------------- 


*
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