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Re: st: is something wrong with fvvarlist "i(3 4).role"?


From   László Sándor <sandorl@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: is something wrong with fvvarlist "i(3 4).role"?
Date   Tue, 13 Jul 2010 02:56:12 +0200

Thank you, Michael!

I acknowledge this behavior, but I find it strange (= not very
intuitive for most uses of this) and also somewhat contrary to the
manual's explanation (below). So I need to add another arbitrary level
just to be able to introduce the level indicators I originally
intended to? How clumsy...

Thanks again,

Laszlo



Selecting levels


    You can select a range of levels -- a range of virtual variables -- by
    using the i(numlist). operator.


         Examples          Description
         --------------------------------------------------------------------
         i2.cat            a single indicator for cat==2


         2.cat             same as i2.cat


         i(2 3 4).cat      three indicators, cat==2, cat==3, and cat==4;
                             same as i2.cat i3.cat i4.cat


         i(2/4).cat        same as i(2 3 4).cat


         2.cat#1.sex       a single indicator that is 1 when cat==2 and
                             sex==1, and is 0 otherwise


         i2.cat#i1.sex     same as 2.cat#1.sex
         --------------------------------------------------------------------

On Tue, Jul 13, 2010 at 2:21 AM, Michael N. Mitchell
<Michael.Norman.Mitchell@gmail.com> wrote:
> Greetings
>
>  The trick is that the -i.- is creating a reference group, so in your
> example group 3 is the reference group. Here are some examples using the
> -auto- dataset.
>
> . sysuse auto
> (1978 Automobile Data)
>
> * group 1 is the reference, groups 2-5 are shown
> . summ   i.rep78
>
>    Variable |       Obs        Mean    Std. Dev.       Min        Max
> -------------+--------------------------------------------------------
>       rep78 |
>          2  |        69     .115942    .3225009          0          1
>          3  |        69    .4347826    .4993602          0          1
>          4  |        69    .2608696    .4423259          0          1
>          5  |        69    .1594203    .3687494          0          1
>
> * group 1 is the reference, groups 2-5 are shown
> . summ   i(1/5).rep78
>
>    Variable |       Obs        Mean    Std. Dev.       Min        Max
> -------------+--------------------------------------------------------
>       rep78 |
>          2  |        69     .115942    .3225009          0          1
>          3  |        69    .4347826    .4993602          0          1
>          4  |        69    .2608696    .4423259          0          1
>          5  |        69    .1594203    .3687494          0          1
>
> * group 1 is the reference, groups 2-4 are shown
> . summ   i(1/4).rep78
>
>    Variable |       Obs        Mean    Std. Dev.       Min        Max
> -------------+--------------------------------------------------------
>       rep78 |
>          2  |        69     .115942    .3225009          0          1
>          3  |        69    .4347826    .4993602          0          1
>          4  |        69    .2608696    .4423259          0          1
>
> * group 1 is the reference, groups 2-3 are shown
> . summ   i(1/3).rep78
>
>    Variable |       Obs        Mean    Std. Dev.       Min        Max
> -------------+--------------------------------------------------------
>       rep78 |
>          2  |        69     .115942    .3225009          0          1
>          3  |        69    .4347826    .4993602          0          1
>
> * group 1 is the reference, group 2 is shown
> . summ   i(1/2).rep78
>
>    Variable |       Obs        Mean    Std. Dev.       Min        Max
> -------------+--------------------------------------------------------
>     2.rep78 |        69     .115942    .3225009          0          1
>
>
> I hope that helps.
>
> Michael N. Mitchell
> Data Management Using Stata      - http://www.stata.com/bookstore/dmus.html
> A Visual Guide to Stata Graphics - http://www.stata.com/bookstore/vgsg.html
> Stata tidbit of the week         - http://www.MichaelNormanMitchell.com
>
>
>
> On 2010-07-12 4.21 PM, László Sándor wrote:
>>
>> Hi all,
>> I think I have a straightforward question in the subject line.
>>
>> I use the up-to-date Stata on a mac. The factor variable handling does
>> not work as promised in the manual (cf. -h fvvarlist-). See the most
>> striking, simple example below. Or am I missing the obvious?
>>
>> Thank you,
>>
>> Laszlo
>>
>>
>>
>> . sum i(3 4).role
>>
>>     Variable |       Obs        Mean    Std. Dev.       Min        Max
>> -------------+--------------------------------------------------------
>>       4.role |       747    .2503347     .433496          0          1
>>
>> . sum i(3/4).role
>>
>>     Variable |       Obs        Mean    Std. Dev.       Min        Max
>> -------------+--------------------------------------------------------
>>       4.role |       747    .2503347     .433496          0          1
>> *
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>> *   http://www.ats.ucla.edu/stat/stata/
>
> *
> *   For searches and help try:
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>

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