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st: Data manipulation with long datasets


From   Sara Mottram <s.mottram@cphc.keele.ac.uk>
To   statalist@hsphsun2.harvard.edu
Subject   st: Data manipulation with long datasets
Date   Mon, 15 May 2006 16:28:15 +0100

Hi,

I am trying to follow the faqs "How do I analyze multiple failure-time data using Stata" (Cleves, 1999) to analyze some data concerning consultation with a family doctor. I think that I need to follow the Andersen and Gill model in section 3.2.1 for what I would like to do. The means that the data need to be in the form:

| id group time0 time status number size |
|------------------------------------------------------|
| 1 placebo 0 1 0 1 3 |
| 2 placebo 0 4 0 2 0 |
| 3 placebo 0 7 0 1 0 |
| 4 placebo 0 10 0 5 0 |
| 5 placebo 0 6 1 4 0 |
|------------------------------------------------------|
| 5 placebo 6 10 0 4 0 |
| 6 placebo 0 14 0 1 0 |
| 7 placebo 0 18 0 1 0 |
| 8 placebo 0 5 1 1 3 |
| 8 placebo 5 18 0 1 3 |
|------------------------------------------------------|
| 9 placebo 0 12 1 1 1 |
| 9 placebo 12 16 1 1 1 |
| 9 placebo 16 18 0 1 1 |
+------------------------------------------------------+
My data are currently in long form with multiple consultations per person and a date for each of these consultations (which I have converted to an edate to allow calculations). I can easily make the date of the consultation representative of the 'time' variable in the example (by subtracting the start time of the study from the consultation date) but I cannot work out how to create an equivalent to the 'time0' variable where I need the time variable from the preceding row to become time0. I thought I might need some sort of within person command but I am struggling to find anything like this.

My data look like this, where duplicate_pp is the number of the consultation in the particular individual:

id cons_dt duplicate_pp
26 05 Jun 00 1
26 18 Aug 00 2
26 13 Oct 00 3
26 10 Nov 00 4
26 25 May 01 5
26 13 Jun 01 6
26 16 Jun 01 7
26 28 Jun 01 8
26 23 Oct 01 9
26 20 Nov 01 10
74 21 Dec 01 1
74 15 Jan 02 2
74 29 Jan 02 3
86 30 Mar 00 1
86 27 Apr 00 2
86 05 May 00 3
86 14 Jun 00 4
86 05 Feb 02 5

Could anyone help me out with creating the time0 variable please?
Thanks
Sara

--
Sara Mottram
Research Assistant: Biostatistics
Primary Care Musculoskeletal Research Centre
Primary Care Sciences
Keele University
Staffordshire, ST5 5BG
Tel: 01782 584711
Fax: 01782 583911
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