Hello Claudio,
this is the trick I use when I want to balance a panel (y is the
outcome variable):
*** begin code
sort id year
by id: egen nonmissing1to7 = count(y) if (year==1 | year==2 | year==3
| year==4 | year==5 | year==6 | year==7)
keep if nonmissing1to7==7
*** end code
Maybe there are more elegant solution around, but this one always
works fine for me.
Best
Davide
2008/5/20 Claudio Cruz Cazares <[email protected]>:
> Dear all!,
>
> I`m working in my Phd. dissertation but a have not find a solution for a crucial problem, hope you could help me.
>
> I have an unbalanced panel data of 4050 firms in 16 years but I have monotone and intermittent (since I clean the data from missing values of my dependent variables) missingness and as far as I know, the intermittent missingnes could cause problems when estimating fist differences.
>
> I wonder if someone could tell me how could I clean the sample. The easiest thing would be to balance it, but even I can see, after xtdes command, how many firms are in all periods, I can not find de way to keep just them. Is there any way to select the firms based upon their pattern?
> Other solution is to eliminate the intermittent observations and keep those who died during the panel and those who growth within the panel, but how can I do that?
>
> I have generated a new variable in order to identify the missingness of a firm in a year.
>
> quietly by Identi: gen dy=year-year[_n-1]
>
> dy would be = 1 if there are non missing observation of the firm. Then, I drop the firms with a dy > 1. But I still have intermittent missigness!
>
> xtdes
>
> Freq. Percent Cum. | Pattern
> ---------------------------+-----------------
> 577 18.89 18.89 | 111111111111111
> 158 5.17 24.06 | 11 . . . . . . . . . . . . .
> 150 4.91 28.97 | 1 . . . . . . 11111111
> 136 4.45 33.42 | . . . . . . . . . . 11111
> 131 4.29 37.71 | 111111111111 . . .
> 126 4.12 41.83 | 1 . . . . . . . . . . . . . .
> 126 4.12 45.96 | 1111 . . . . 111 . . . .
> 116 3.80 49.75 | 111 . . . . . . . . . . . .
> 88 2.88 52.64 | 111111 . . . . . . . 11
> 1447 47.36 100.00 | (other patterns)
> ---------------------------+-----------------
> 3055 100.00 | XXXXXXXXXXXXXXX
>
>
>
>
> Thanks in advance
>
> Claudio
>
>
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