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Re: st: Intraclass Correlation for an Independent Variable?


From   Steve Samuels <sjsamuels@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Intraclass Correlation for an Independent Variable?
Date   Thu, 12 Aug 2010 12:43:04 -0400

Lloyd, Whether, and how, to include the worker measurements as
predictors of plant outcomes are substantive questions that I don't
think I can answer.

Steve

On Thu, Aug 12, 2010 at 12:22 PM, Lloyd Dumont <lloyddumont@yahoo.com> wrote:
> Thank you for your advice on this, Steve.  From a technical/statistical point-of-view, it was very helpful.  I ran -loneway- on the dataset of individual workers.  The F-stat was about 1.24, generating a p-value far greater than I would have wanted in order to please the reviewer--about .24.
>
> Given that, is there anything I can do to make the case for these measures?  Is there a way to "correct for" the heterskedasticity of the estimated means for each plant before collapsing them into a dataset of plant-months?  Off the top of my head, the first thing I thought of was to -collapse- the data using medians as opposed to means.  That way, I could at least be assured that outliars are not influencing each plant's score.  Interestingly, when I did that, the results in the regression of plant-months became a little stronger.
>
> Thank you again.  Lloyd
>
> --- On Wed, 8/11/10, Steve Samuels <sjsamuels@gmail.com> wrote:
>
>> From: Steve Samuels <sjsamuels@gmail.com>
>> Subject: Re: st: Intraclass Correlation for an Independent Variable?
>> To: statalist@hsphsun2.harvard.edu
>> Date: Wednesday, August 11, 2010, 5:47 PM
>> I didn't read the second part of your
>> message closely enough.  ICCs
>> can be computed for any variable measured in groups,and the
>> reviewer's
>> terminology is impeccable.  -loneway- should do what
>> you want. But
>> "search intraclass, all" will find some extensions.
>>
>> Steve
>>
>> On Wed, Aug 11, 2010 at 5:05 PM, Steve Samuels <sjsamuels@gmail.com>
>> wrote:
>> > The reviewer could well want to know if the plant
>> differences in the X
>> > means are real.  So, yes, he or she could really mean
>> "X".  This is
>> > the kind of question you'd test with a one-way ANOVA,
>> or KW. You will
>> > need the data from the individual worker X
>> measurements, or the
>> > plant-specific sample sizes and  variances.
>> >
>> > Steve
>> > On Wed, Aug 11, 2010 at 4:36 PM, Lloyd Dumont <lloyddumont@yahoo.com>
>> wrote:
>> >> Hello.  I have gotten a confusing note from a
>> reviewer, confusing in part because I think he/she is using
>> the wrong terminology.
>> >>
>> >>
>> >> In a nutshell…
>> >>
>> >> I am running a cross-sectional time series model
>> (on a dataset of plant-months) of a continuous variable Y
>> measured at the plant level where the focal, continuous
>> independent variable is X.  X is also at the plant-level,
>> but is time-constant.  X is formed by taking the mean level
>> of X from all of the individual workers in each plant.
>> >>
>> >> The reviewer suggests that I include some measure
>> of within versus between plant variance in X.  This would
>> bolster the case that there is a genuine difference across
>> plants rather than average differences simply reflecting
>> noise.  He/she then goes on to suggest I do this by
>> reporting intraclass correlations (ICCs).
>> >>
>> >> As far as I understand it, ICCs (or rho) describe
>> the variance in Y, not X.  If I am right, then the reviewer
>> did not mean ICC.
>> >>
>> >> Rather, he/she wants me to go back to the dataset
>> of individuals (not plant-months) and wants me to run some
>> simple analysis to show that there is clustering of values
>> for X by plant.
>> >>
>> >> Am I correctly understanding what the reviewer is
>> asking for?  And, if so, what is the simplest way to
>> demonstrate the sort of dependence he/she is hoping to see?
>> >>
>> >> Thank you for your help.  Lloyd
>> >>
>> >>
>> >>
>> >>
>> >>
>> >>
>> >> *
>> >> *   For searches and help try:
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>> >>
>> >
>> >
>> >
>> > --
>> > Steven Samuels
>> > sjsamuels@gmail.com
>> > 18 Cantine's Island
>> > Saugerties NY 12477
>> > USA
>> > Voice: 845-246-0774
>> > Fax:    206-202-4783
>> >
>>
>>
>>
>> --
>> Steven Samuels
>> sjsamuels@gmail.com
>> 18 Cantine's Island
>> Saugerties NY 12477
>> USA
>> Voice: 845-246-0774
>> Fax:    206-202-4783
>>
>> *
>> *   For searches and help try:
>> *   http://www.stata.com/help.cgi?search
>> *   http://www.stata.com/support/statalist/faq
>> *   http://www.ats.ucla.edu/stat/stata/
>>
>
>
>
>
>
> *
> *   For searches and help try:
> *   http://www.stata.com/help.cgi?search
> *   http://www.stata.com/support/statalist/faq
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>



-- 
Steven Samuels
sjsamuels@gmail.com
18 Cantine's Island
Saugerties NY 12477
USA
Voice: 845-246-0774
Fax:    206-202-4783

*
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