Statalist


[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

st: RE: RE: Nested loops by observation


From   David Sabapathy <[email protected]>
To   "[email protected]" <[email protected]>
Subject   st: RE: RE: Nested loops by observation
Date   Mon, 20 Jul 2009 11:58:55 -0600

Thank you very much for your reply.  You are correct in that I am figuring out how Stata works relative to some other software I used eons ago.  I also have a gut instinct this is not the way to go. A sample of my dataset is as follows:
Obs  dgc1_1b_cde  dgc2_1b_cde  dgc3_1b_cde  dgc4_1b_cde  dgc5_1b_cde  dgc6_1b_cde  dhc1_age  dhc2_age  dhc3_age ..... dhc6_age  chronic
1               0                     1                 1                       1                     0                       1                    20            22             24                 30           .
2               0                     1                 0                       1                     0                       1                    66            68             70                 76           .
3               0                     0                 0                       0                     1                       1                    34            36             38                 44           .
4               1                     1                 0                       1                     0                       1                    42            44             46                 52           .
... N>15000
Each observation represents one individual's responses to a medication survey administered 6 consecutive times or cycles. The "dgc" variables represent a binary response to whether this individual is taking a certain medication (1=yes).  The fourth character in the "dgc" variables e.g. dgc"1" represents the cycle number.  e.g. the first individual did not take the medication in cycle 5 (dgc5_1b_cde==0) but did in cycle 6 (dgc6_1b_cde==0). I am defining incident chronic usage of this medication as the patient not taking the medication in any cycle i followed by taking the medication for two consecutive cycles i+1 and i+2.  That is you need a sequence of three cycles starting with a "0" and followed by two "1s".  Above, observations 1 and 3 qualify as being chronic incident usage of the medication, 2 and 4 do not.  The "dhc" variables in my code are just the individuals age.  I thought of setting the "chronic" variable if the incidient chronic usage condition was met but it ce!
 rtainly looks like a new approach is needed.

David Sabapathy

________________________________________
From: [email protected] [[email protected]] On Behalf Of Nick Cox [[email protected]]
Sent: July 20, 2009 10:59 AM
To: [email protected]
Subject: st: RE: Nested loops by observation

My visceral instinct, fortified by some Stata experience, is that this
is not the way to go at all. That is, I guess that your second sentence
is quite wrong: you don't need to do it this way at all.

This looks like the code of someone experienced in some alternative
software, but less so in Stata. In Stata, loops over observations are
rarely needed given the scope for using -by:- and _n.

Give an example of your data and a precise definition of chronic
condition and I will try to advise further. (I'm not going to try to
infer your definition from your code.)

Nick
[email protected]

David Sabapathy

I have a question related to the FAQ "if command versus if qualifier".
For each observation in a dataset I need to perform a series of nested
loops ("forvalues" / "if") on a longitudinal variable set to evaluate
whether a "chronic" medication condition exists.  That is, each
observation contains multiple years of survey information (the dgc*
variables below) which is being analyzed and if a chronic condition
exists a new variable "chronic" is set to 1.  I can't use the nested
commands as shown below in a simplified version of the code as they only
work on the first observation.  However I also can't use this nested
code as a qualifier (i.e. replace chronic = 1 if ...) as syntax does not
appear to allow this type of nesting.  Is there anyway I can step
through observations one by one with this nested code?  Any other
possible solutions?
Thank you for any help you can provide,
David

gen chronic = .

forvalues cycle = 1(1)4 {
     if dgc`cycle'_1b_cde == 0 {                       // if no med use
cycle i
          local chron_cyc1 = `cycle' + 1
          if dgc`chron_cyc1'_1b_cde == 1 {       // if med use cycle_i+1
               local chron_cyc2 = `cycle' + 2
               if dgc`chron_cyc2'_1b_cde == 1 {  // if med use cycle_i+2
                    if dhc`chron_cyc1'_age >=65 & dhc`chron_cyc2'_age
>=65 {
                         // "replace chronic = 2"
                         }
                   else {
                          // "replace chronic = 1"
                          }
                   }
              }
        }
}


*
*   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/

This message and any attached documents are only for the use of the intended recipient(s), are confidential and may contain privileged information. Any unauthorized review, use, retransmission, or other disclosure is strictly prohibited. If you have received this message in error, please notify the sender immediately, and then delete the original message. Thank you.

*
*   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/



© Copyright 1996–2024 StataCorp LLC   |   Terms of use   |   Privacy   |   Contact us   |   What's new   |   Site index