Bookmark and Share

Notice: On March 31, it was announced that Statalist is moving from an email list to a forum. The old list will shut down on April 23, and its replacement, is already up and running.

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: st: Unbalanced repeated measures analysis question

From   K Jensen <>
Subject   Re: st: Unbalanced repeated measures analysis question
Date   Thu, 22 Jul 2010 11:33:05 +0100

Thanks to Robert and David for your helpful comments. Sorry to sound
stupid here but mixed models are entirely new to me. I have been
reading up on them.

I have the variables outlined below:
SubjectID MeasurerID MeasurerType Result GoldStandard
where MeasurerID is always a certain MeasurerType (1-3)

SubjectID and MeasurerID should be random effects and MeasurerType
fixed?  How would you specify that in the xtmixed syntax?  I am
confused about having two grouping variables for the random effects.


On 21 July 2010 22:37, Ploutz-Snyder, Robert (JSC-SK)[USRA]
<> wrote:
> Karin,
> I feel your pain RE Stata's anova syntax for repeated measures...
>  But I also agree with David that I think your better bet is
> probably to use -xtmixed- and then apply -margins- for  your
> post-hoc comparisons, given the imbalance issue.  You can use
> -margins- to compare each of the three measures to the gold
> standard--akin to simple effect contrasts.
> If you wish to remain in the anova syntax, you might want to
> check out the user written -anovalator- command, thanks to Phil
> Ender from UCLA.  But from the sounds of your imbalanced design,
> I would tend to lean more to -xtmixed- with -margins-
> (BTW--the Phil's website at UCLA has some nice walk-throughs
> of all of this.)
> Rob
> -----Original Message-----
> From: [] On Behalf Of Airey, David C
> Sent: Wednesday, July 21, 2010 4:07 PM
> To:
> Subject: re: st: Unbalanced repeated measures analysis question
> I think when you have comparisons to a gold standard, or all
> comparisons with one control, that there are specific ANOVA
> post-hoc tests that perform better than all possible or all
> pairwise comparisons procedures.
> There is the complication that you are testing for equivalence,
> as you say.
> The Stata command -xtmixed- can do what -anova- can. Sometimes
> -manova- or -mvtest- is useful with repeated measures too.
> It is hard to understand how your design is unbalanced without
> seeing the data cross-tabs, etc.
>> Hi
>> I have data on measuring a biological property for three different
>> methods plus a gold standard. Different people were trained in each
>> method (1,2 or 3) and measured the same subjects during different
>> sessions, together with the gold standard measurement.
>> So the data look like
>> SubjectID MeasurerID MeasurerType Result GoldStandard  Diff
>> 1         1          1            95     99            -4
>> 1         2          3            102    99            +3
>> 1         3          2            92     99            -7
>> ...
>> 1        10          3            105    99            +6
>> 2         1          3             98   100            -2
>> ...
>> Sometimes patients would be called in to see the consultant and so
>> missed for a particular measurer, but otherwise all the measurers
>> would measure all the patients seen in a particular session. Different
>> sets of measurers (but all trained by methods 1,2 or 3) were used on
>> each session (individual measurers 1-10 on session 1, 11-20 on session
>> 2 etc).
>> The gold standard measurements on each session are roughly normally
>> distributed, as are the differences from the gold standard. We are
>> interested in the accuracy of each of the three methods.
>> Is it OK to do some sort of repeated measures ANOVA here, with an
>> unbalanced design? If it is what would be the syntax (Stata 10)? Sorry
>> to sound pathetic but I just can't get the anova command with the
>> repeated option to work here.
>> Is there a better measure to use than the difference to reflect the
>> fact that we are interested in a comparison with a gold standard?
>> Thankyou
>> Karin

*   For searches and help try:

© Copyright 1996–2016 StataCorp LP   |   Terms of use   |   Privacy   |   Contact us   |   Site index