This has me tearing my (sparse enough) hair out, thought
I'd share that experience with others...
I have prescription data on patients (-id-); once they start on a
diabetic medication (-medcat-), they can either stay on it, switch, or
add a new one. For each prescription, there is the number of -days-
the script is good for. Here is one patient, where I have also calculated
the -gap- in days between each fill date:
+--------------------------------------------+
| scrssn date medcat days gap |
|--------------------------------------------|
| 1081 16 Feb 00 1 90 . |
| 1081 05 May 00 6 90 79 |
| 1081 06 May 00 1 90 1 |
| 1081 25 Jul 00 2 90 80 |
| 1081 01 Aug 00 5 90 7 |
| 1081 26 Sep 00 1 90 56 |
| 1081 22 Oct 00 5 90 26 |
| 1081 01 Nov 00 2 90 10 |
| 1081 23 Jan 01 1 90 83 |
| 1081 01 Feb 01 2 90 9 |
So this patient started on medcat=1, for 90 days, but after 79 days
got a different med, medcat=2, but refilled the original medcat=1
on day 80. This means that the second record indicates an "add"
instead of a "switch". However, the next time they got their start
med was on 26 Sep 2000, 80+7+56 = 143 days after 6 May, so the
med on 25 Jul 2000 represents "switch" to medcat=2, and the med
on 26 Sep 2000 represents a switch back to the original med.
What I need to do is operationalize this logic, and mark every
record that is not the index med (first medication) as either
a switch, an add, or a continuation. I have written piles of
useless code for this today, and imagine I am missing some
very useful insight/adofile/nerve that would do the trick. Rather
than paste in the broken bits here, I thought I'd leave it open
for free-thinking listers... Any pointers?
Other info:
it is just chance that all of the -days- here are 90; many patients
also have 14 & 30 day scripts)
there are only 6 distinct -medcat- medication categories, so they
could be handled one at a time
as long as the last record is within the -days- covered by the last
switched or continued medcat, it is considered an -add-
I keep thinking the solution is of the form
bys scrssn (date) : <loop over 1/_N for each record>
but can't see a way to do it.
thanks in advance,
Jeph
--
Jeph Herrin
[email protected]
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