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Re: st: mean centering


From   Nick Cox <njcoxstata@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: mean centering
Date   Sun, 20 Jan 2013 15:42:04 +0000

The easiest way to subtract an overall mean is to use -summarize-

summarize var, meanonly
gen centered_var = var - r(mean)

Creating a variable to hold a constant mean is usually unnecessary and
always inefficient.

Nick

On Sun, Jan 20, 2013 at 3:15 PM, Aljar Meesters
<aljar.meesters@gmail.com> wrote:
> Dear James,
>
> I think that in general one centers variables to make the
> interpretation of the marginal effects, conditional on the averages,
> easier.
> Centering variables in a pane should be based on the means of all the
> observations of the particular variables and never by groups. If you
> deducted the means of groups, you are carrying out a within
> transformation, which will lead to a fixed effects model, which is
> certainly not your goal of centering the variables.
> You can do this by:
> egen meanvar = mean(var)
> gen centered_var = var - meanvar
>
> best,
>
> Aljar
>
> 2013/1/20 James Bernard <jamesstatalist@gmail.com>:
>> Hi,
>>
>> I know that mean centering is not really a remedy for the resultant
>> multidisciplinary among interaction effect variables. But, it has
>> become a common practice. I have two questions:
>>
>> 1- In the case of panel data: should we deduct the mean of all the
>> observations of that particular variables or should we do this by
>> groups of observation?
>>
>> 2- is there any direct command in Stata for mean centering?
>>
>> Thanks,
>> james
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