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Re: st: Count the number of changing string values


From   Ching Wong <ching.y.wong@student.adelaide.edu.au>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Count the number of changing string values
Date   Fri, 14 Jun 2013 20:15:30 +0930

Hi Nick,

So what if -drug*- are numeric variables with value labels, how should
I change my Command?


Thanks!


Ching

On 14 June 2013 19:19, Nick Cox <njcoxstata@gmail.com> wrote:
> Code that "doesn't work" but is not shown can not be commented on.
> Long structure (I prefer to avoid the word "format" here) is not
> essential for the problem as I understand it, but it is likely to be
> better for you for most analyses.
>
> The year in which people first said "No" is
>
> gen year = .
>
> qui forval j = 1999/2012 {
>         replace year = `j' if  Drug`j' == "No" & missing(year)
> }
>
> tab year
>
> So,
>
> 1. Everybody starts out with missing.
>
> 2. If they said "No" in 1999, -year- is changed to 1999
>
> 3. If they said "No" in 2000, -year- is changed to 2000, but only if
> -year- is missing (so values of 1999 are protected)
>
> and so on.
>
> You didn't explain your datatypes. If -drug*- are numeric variables
> with value labels, the syntax will differ accordingly.
>
> Nick
> njcoxstata@gmail.com
>
>
> On 14 June 2013 10:20, Ching Wong <ching.y.wong@student.adelaide.edu.au> wrote:
>
>> I have the following data set:
>>
>> Id     sex   drug1999   drug2000    drug2001      drug 2001
>>
>> 1       F       Yes            No          Yes            Unknown
>>
>> 3       M       No           Yes          Yes             No
>>
>> 5      F         Yes          Yes          Yes            Yes
>>
>> 9      M       Unknown    Yes          No             Yes
>>
>> 10     F        Yes           No           Yes             No
>>
>> I would like to produce a count of to show the number of people who
>> quit each year, only count the first time they quit and do not care if
>> they change their status to ‘No’ again.
>>
>> What would be the command? I tried to change it to the long formal and
>> use the lag function, but it doesn’t work.
>
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