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Re: st: How to drop low frequency patterns from panel data


From   Nick Cox <njcoxstata@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: How to drop low frequency patterns from panel data
Date   Fri, 3 Feb 2012 09:35:06 +0000

-xtpatternvar- is a user-written command from SSC. Please remember to
explain where user-written programs you refer to come from.

bysort pattern : drop if _N < 20

is I think what you seek.

Nick

On Fri, Feb 3, 2012 at 9:22 AM, Kim Peeters <kimpeeters84@yahoo.com> wrote:

> I have an unbalanced panel data set. The yearly data spans a period of almost twenty years. However, most subjects only participated in the last years of the study, which is confirmed by the analysis of the different panel patterns using -xtdescribe-. While some patterns' frequency is >1000, other patterns only occur once. To improve the data quality, I would like to drop all patterns that occur less than twenty times.
>
> I have not been able to accomplish this. Thus far, I can only re-generate the -xtdescribe- output again.
> xtpatternvar,gen(pattern)
> egen tag =tag(ID)
> tabulate pattern if tag, sort
>
> Any advice on how to drop low frequency patterns from panel data?

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