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st: Artificial censoring in survival analysis


From   melaku.fekadu@gmail.com
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   st: Artificial censoring in survival analysis
Date   Tue, 2 Aug 2011 10:25:27 +0300

Hello statalisters,

I analyze employment data using survival method for a length of 12 months. I decided to do so because some of my observations are younger to experience the event (in this case exiting unemployment) for more than 12 months; that is I observe them only for 12 months. To overcome this problem I imposed a 12 months period of analysis for all of my observations. That is all observations have equal length of 12 months to experience the event. I did so by artificially censoring those observations for whom I have data for more than 12 months and did not experience the event within 12 months. These are old individuals. I did censor even though I see some of these observations experience the event later, after the 12 months period.

My questions: 
1. Should I include in the analysis those observations that I censored?
2. Is the sample data presented below appropriate for survival analysis? Note that all of observations experience the event except those I censored at the 12 month.

Below is a small representation of my data. The failure variable 'Failure' is cross-tabulated with the variable 'studytime' which is the number of months until experiencing the event.

   Failure
   0 | 1
    ------
1    0 | 200
2    0 | 89
3    0 | 70
5    0 | 68
6    0 | 58
7    0 | 50
8    0 | 51
10   0 | 45
11   0 | 30
12   150 | 0

Thanks,
Melaku

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