
From  Ronán Conroy <rconroy@rcsi.ie> 
To  statalist@hsphsun2.harvard.edu 
Subject  Re: st: Interpreting conditional logistic regression equations using 2 similar types of matching. 
Date  Wed, 7 Feb 2007 10:28:22 +0000 
On 6 Feabh 2007, at 23:40, Donald Spady wrote:
This may be a second posting. The first one did not seem to go through andI'm not sure I understand this design. Children can have more than one seizure, so is your case variable whether the child ever had a seizure or never had a seizure, or are you doing a nested case control and matching a child in whom a seizure occurred with a child of the same age in whom one did not occur?
on reading the FAQ I realized that I might have sent nonplain text. (I
copied the output from Stata using the copy table command rather than the
copy text command. Hopefully this one will work.)
I am looking at the effect of irondeficiency anemia on the likelihood of a
child having a seizure.
Age is a measure of exposure to risk. This, and the fact that cases are defined by the occurrence of an event, suggest survival models here rather than conditional logistic regression.I am using clogit but have a problem in that I have matched my case/control "group" variable (age) as either very tightly matched (same month: "tight") or more loosely matched (up to 3 months difference: "loose").
The whole age range of difference is 30 months, so 3You are losing cases (output omitted) with both of your current designs, which is going to lower your power and, I'm guessing, bias the estimates in ways you can't predict but have certainly demonstrated.
months is still fairly closely matched. When I do the 2 clogit equations I
get different Odds ratios (which seems OK), but don't know which one is the
'right' one to use. Any help would be appreciated.
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