<>
It is difficult for an outsider to make up data for your specific problem;
therefore either frame the prob in terms of a dataset shipped with Stata or
-set trace on- and report the area around the error...
HTH
Martin
-----Ursprüngliche Nachricht-----
Von: [email protected]
[mailto:[email protected]] Im Auftrag von Ilona Carneiro
Gesendet: Freitag, 27. Februar 2009 19:09
An: [email protected]
Betreff: Re: st: AW: RE: Problem looping over spells for an individual
Thanks for these suggestions, Nick. Some of them seem to require
"tsset"ing the data. However, I am trying to adapt the code from
panelthin.ado, but can't quite get it to work for me. I've been
battling with this for a couple of days now and I can't seem to find a
way to loop over consecutive observations for an individual. I see
that in panelthin, it automatically works separately on each panel
because it is tsset, but how can I do this for survival time "stset"
data?
I've written a little sub-programme to see if I can get this to work.
Generation of a local for _N now works and does give the correct count
of observations per individual. However, my generation of the tempvar
`t' to define the sequential observations (_n) for each individual
doesn't work. Any suggestions?
capture program drop temp
program define temp, byable(recall, noheader) sortpreserve
qui{
marksample touse
count if `touse'
if r(N) == 0 error 2000
tempvar T t
sort `_byvars' start
by `_byvars': gen `t' = _n * `touse'
sort `_byvars' start
by `_byvars': gen `T' = _N * `touse'
sort `_byvars' start
sum `T', meanonly
local tmax = r(max)
drop `T'
replace lagend = (end + 19 + 1) if (anmal > 0 & anmal < .)
sort pin start
forvalues i = 1(1)`tmax' {
drop if end < lagend[`i'-1] & lagend[`i'-1] < . &
`t'==`i' & `i'!=1
replace lagend = (end + 21 + 1) if (mal0 > 0 & mal0
< .) &
lagend==. & `i'<`tmax'
}
}
end
bysort id: temp
regards
Ilona
On 26 Feb 2009, at 13:20, Nick Cox wrote:
> Thanks for this, which is good news for me because it explains why
> the code I was seeing looked as it did.
>
> In terms of moving forward, I have a few vague suggestions.
>
> 0. Spells. See the suggestions on reading and software in the thread
> started by Jakob Petersen yesterday.
>
>
<http://www.hsph.harvard.edu/cgi-bin/lwgate/STATALIST/archives/statalist.090
2/date/article-1122.html
> >
>
> 1. One is more of style or taste than technique. I prefer to think
> in terms of tagging observations I want to keep or work on with 1
> and those I don't with 0. Then you can do almost anything later
>
> ... if tag
>
> or
>
> ... if !tag
>
> as the case may be.
>
> An advantage of that style: it is reversible, both within an
> algorithm and generally.
> (If you really want to -drop- observations, -drop- them in one go
> when the selection is final.)
>
> 2. One strategy might be
>
> loop over individuals {
> -expand- each individual to a block of observations with one
> observation per day
> <magic bit>
> reduce each individual back again
> }
>
> 3. This problem reminds me loosely of one tackled with -panelthin-
> on SSC. The code for that may suggest some technique.
>
> Nick
> [email protected]
>
> Ilona Carneiro
>
> Many thanks to Nick & Martin for pointing out my error using "if" -
> you are correct and that's why it wasn't working. However, I'm still
> unable to do what I wanted to. Apologies for posting code which I
> tried to simplify, but just made incomprehensible! The snippet was
> part of a much larger programme in which the other local macros are
> all defined.
>
> I'll try to clarify. Here is an example of the problem I have. These
> are consecutive periods of observations for an individual - the end
> denoted by a clinic visit which may or may not be defined as a case
> (depending on diagnostic result), or by exit from the study.
>
> id start end case tx
> 1 10 20 1 1
> 1 20 35 1 0
> 1 35 50 1 0
> 1 50 100 . .
>
> I need to exclude 19 days at risk if the patient received treatment
> (tx==1) as this is considered to be prophylaxis, and to avoid counting
> the same episode (case==1) twice I also exclude 19 days at risk after
> a case is diagnosed. However, as the latter is only to prevent double-
> counting it is not necessary if the case has already been
> disqualified.
>
> What I need to get is the following:
>
> id start end case tx
> 1 10 20 1 1
> 1 40 50 1 0
> 1 50 100 . .
>
> I originally coded the following VERY crudely:
>
> /* To calculate the gaps */
> sort id start
> by id: gen lagend = end + lag if (tx > 0 & tx < .) | (case > 0 & case
> < .) & _n!=_N
>
>
> /* To drop periods of time that are disqualified - repeated 3 times as
> there may be up to 3 consecutively - to be generalisable, it could be
> more */
> sort id start
> by id: drop if lagend[_n-1] > end & lagend[_n-1] < . & _n!=1
> sort id start
> by id: drop if lagend[_n-1] > end & lagend[_n-1] < . & _n!=1
> sort id start
> by id: drop if lagend[_n-1] > end & lagend[_n-1] < . & _n!=1
> sort id start
> by id: drop if lagstart > end & lagstart < . & _n!=1
>
> /* To update the start date */
> sort id start
> by id: replace start = lagend[_n-1] if lagend[_n-1] < . & _n!=1
> sort id start
> by id: drop if (end < start | start[_n-1] > end) & end < . & start < .
> & _n!=1
>
> This works fine for adding a gap after each treatment, as I need to do
> this even if the observation period is dropped from the time at risk.
> The code gave the following result, as both the 2nd & 3rd episodes
> were disqualified, instead of just the 2nd:
>
> id start end case tx
> 1 10 20 1 1
> 1 55 100 . .
>
> I realise that I need to evaluate the generation of the gap after
> cases separately for each observation period, incase the observation
> is dropped. But can't seem to find a way to do this. I hope this is a
> clearer explanation of the problem.
>
> On another point, I subsequently use stgen gap = gaplen() to
> calculate how much time to exclude from the time at risk. Stata
> appears to count one more than just the actual gap, i.e. it will give
> me a gap of 20 days between an observation ending with day 20, and a
> subsequent observation starting at day 40, when the actual time
> excluded in-between is 19 days. I'm just subtracting 1 from the
> calculation at present, but is there a reason for this?
>
> Ilona
>
>
>
> On 25 Feb 2009, at 18:27, Martin Weiss wrote:
>
>>
>> <>
>>
>>
>> I was desperate to find an SJ tip for Ilona on the difference
>> between "if"
>> and "if"; turns out it is an FAQ:
>> http://www.stata.com/support/faqs/lang/ifqualifier.html
>>
>>
>>
>>
>> HTH
>> Martin
>>
>>
>> -----Ursprüngliche Nachricht-----
>> Von: [email protected]
>> [mailto:[email protected]] Im Auftrag von Nick Cox
>> Gesendet: Mittwoch, 25. Februar 2009 18:22
>> An: [email protected]
>> Betreff: st: RE: Problem looping over spells for an individual
>>
>> Unless you are working under the aegis of -by:- _N will always be
>> interpreted as the total number of observations. This code doesn't
>> satisfy that.
>>
>> I echo Martin Weiss in suspecting that your -if `touse'- is a bug.
>> You
>> are almost certainly confusing the two flavours of -if-.
>>
>> Otherwise, your code still looks very confused and based on a
>> variety of
>> misunderstandings. Apart from `touse', which is defined by -
>> marksample-,
>> all of the local macros you refer to will be treated as empty
>> strings,
>> as none has been defined earlier in the program. I am surprised to
>> hear
>> that it is running at all.
>>
>> It does not look as if you need a program anyway. My impression is
>> that
>> all you need is to use -by:- but I don't understand your problem well
>> enough to suggest better code. Someone else may be able to give
>> better
>> help. If not, rather than a lengthy word description, you should
>> perhaps
>> give an example of your data with the intended result.
>>
>> Nick
>> [email protected]
>>
>> Ilona Carneiro
>>
>> I am trying to write a programme that will run a command sequentially
>> for observations of an individual. For each individual I have
>> multiple
>> spells and multiple failures. However, the twist is that I also need
>> to exclude a period of time at risk after each treatment
>> (prophylaxis)
>> and after each failure (to prevent double-counting of failures that
>> may actually be the same episode). I managed to do this without any
>> problem for the treatment, but if an episode is disqualified (by a
>> prior treatment or episode) I don't want it to disqualify a
>> subsequent
>> episode. Therefore I need to run the code sequentially for each spell
>> of an individual, but using the marksample touse code to run it "by"
>> individual doesn't seem to be working - the "forvalues" seems to
>> always interpret _N as the last observation in the whole dataset, not
>> the last observation for each individual.
>>
>> I have the following code:
>>
>> program define byid, byable(recall, noheader)
>> marksample touse
>> sort `id' `start'
>> if `touse' {
>> forvalues i = 1(1)`=_N' {
>> replace lagend = (`end' + `lag') if ((`tx' > 0 & `tx' <
>> .) | (`case'
>>> 0 & `case' < .))
>> drop if lagend[`i'-1]>`end' & `id'[`i'-1]==`id'
>> }
>> }
>> end
>>
>> gen lagend=.
>> qui by id: byid
>>
>> but I get the error:
>> 2nd by group not found
>> r(111);
>>
>> And the programme isn't doing what I need it to.
>>
>>
>> *
>> * For searches and help try:
>> * http://www.stata.com/help.cgi?search
>> * http://www.stata.com/support/statalist/faq
>> * http://www.ats.ucla.edu/stat/stata/
>>
>>
>> *
>> * For searches and help try:
>> * http://www.stata.com/help.cgi?search
>> * http://www.stata.com/support/statalist/faq
>> * http://www.ats.ucla.edu/stat/stata/
>
>
> *
> * For searches and help try:
> * http://www.stata.com/help.cgi?search
> * http://www.stata.com/support/statalist/faq
> * http://www.ats.ucla.edu/stat/stata/
>
> *
> * For searches and help try:
> * http://www.stata.com/help.cgi?search
> * http://www.stata.com/support/statalist/faq
> * http://www.ats.ucla.edu/stat/stata/
*
* For searches and help try:
* http://www.stata.com/help.cgi?search
* http://www.stata.com/support/statalist/faq
* http://www.ats.ucla.edu/stat/stata/
*
* For searches and help try:
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* http://www.stata.com/support/statalist/faq
* http://www.ats.ucla.edu/stat/stata/
