Re: st: RE: perform regression on minimum number of observations stata

[Nick Cox <njcoxstata@gmail.com>]

Gregorio's loop can be modified something like this

forval y=1989/2012 {
      forval  i= 1/57 {
        di "year = `y' and industry = `i'"

      reg DV IV_1 IN_2 IN_3 if  Industry== `i' & year==`y' & nobs>15
}
Nick
njcoxstata@gmail.com


On 29 July 2013 16:15, Nahla Betelmal <nahlaib@gmail.com> wrote:
> Thanks Gregorio, but how can I exclude the regression with less than
> 15 observation due to missing data rather than no observation? any
> idea!
>
>  many thanks again for the great help. from what I have read in the
> field the magic number is 15, one or two papers uses 20. Maybe due to
> the nature of the data availability from the population dataset.
>
> Thanks again for the kind help
>
> Nahla
>
> On 29 July 2013 15:57, Impavido, Gregorio <GImpavido@imf.org> wrote:
>> You could modify your loop as follows:
>>
>> bysort year industry: gen nobs = _N
>> forval y=1989/2012 {
>>       forval  i= 1/57 {
>>         di "year = `y' and industry = `i'"
>>       reg DV IV_1 IN_2 IN_3 if  Industry== `i' & year==`y' & nobs>15
>> }
>>
>> However, I thought that the "magic number" for the central limit theorem to apply was 30.
>>
>> -----Original Message-----
>> From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Nahla Betelmal
>> Sent: Monday, July 29, 2013 10:32 AM
>> To: statalist@hsphsun2.harvard.edu
>> Subject: st: perform regression on minimum number of observations stata
>>
>> Hi Statalist,
>>
>> my data consists of several years and several industries (each industry contain several firms). I run  cross-sectional regressions as follow :
>>
>> forval y=1989/2012 {
>>       forval  i= 1/57 {
>>            reg DV IV_1 IN_2 IN_3 if  Industry== `i' & year==`y'
>> }
>>
>> I have two questions please:
>>
>> 1- According to literature, any industry-year regression with less than 15 observations (i.e. 15 firms) should be disregarded. the tricky thing is that almost every industry-year group has more than 15 firms but some are with missing values to perform the regression. Therefore, the regression could be done with less than 15 observation. How can I account for this in the above loop, so regression with less than 15 complete observations produce missing values instead of actual values!
>>
>> 2- the output does not provide information about the matched year and industry. Is there a way to do it?  I only need that for reporting purpose.
>>
>> Thank you
>>
>> Nahla Betelmal
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