# st: Simple programming question?

 From "Anderson, Bradley J" To "'statalist@hsphsun2.harvard.edu'" Subject st: Simple programming question? Date Tue, 17 Oct 2006 16:39:07 -0400

```Though I seem to be too simple to figure it out.

I have data like the following:

id day1 day2 day3 day4 day5 day6 ... day90
1  0    0    0    1    0    0    ... 0
2  0    0    0    0    1    1    ... .
3  1    1    1    1    1    1    ... 1
4  0    0    0    0    0    0    ... 0

Assume that a 1 on day`i' represents failure.  I'm trying to generate a
variable that gives days to failure for survival analysis.  E.g., subject 1
failed on day 4, subject 5 failed on day 5, subject 3 failed on day 1,
subject 4 did not fail and would be considered censored.  90 days worth of
data were collected but not all subjects were observed for the full 90-day
period.  Also note that subjects may be recorded as failing (drinking at
hazardous levels) on any combination of days during the 90-day period.  I'm
trying to calculate number of days to first failure.  Seems like it should
be simple but I'm sufficiently naive that I've not solved it.  Thanks.

-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu]On Behalf Of Nick Cox
Sent: Tuesday, October 17, 2006 1:16 PM
To: statalist@hsphsun2.harvard.edu
Subject: st: RE: Manipulating variables with repeated observations

You should find out about -by:-.

For example:

bysort MRN (VisitDate) : gen visit = _n
by MRN : gen change = BMI[_N] - BMI[1]

Nick
n.j.cox@durham.ac.uk

Karen R. Flórez

> I have a dataset with kids BMIs that looks like this:
>
> MRN     VisitDate   BMI
>
> 123     10/20/04    30
>
> 123      6/11/05    25
>
> 123      4/14/06    25
>
> 222
>
> 222
>
> 222
>
>
>
> Where MRN is the unique identifier. Kids had different visits at
> different times and BMI were take at each time. How can I generate
> a variable that codes for Visit 1,2,3,etc? So that I can measure
> the change between baseline and last follow-up?

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```