[R] Surv(): Stop time must be > start time, NA created

[Federico Calboli]

On 3 Jun 2011, at 11:27, Dimitris Rizopoulos wrote:

> this sounds like a competing risks problem. Maybe you would be interested in a cause-specific hazard regression or the Fine & Gray model (http://cran.r-project.org/package=cmprsk).

I will look into that,but, biologically, parkinson leads to dementia (cause and effect rather than competing risk), and in fact all my subjects do have parkinson. Unless the two competing risks are 'risk of dementia' vs 'risk of death'.

Best

F

> 
> Recently there was also a special issue in JSS on this topic (http://www.jstatsoft.org/v38).
> 
> I hope it helps.
> 
> Best,
> Dimitris
> 
> 
> On 6/3/2011 12:17 PM, Federico Calboli wrote:
>> I am writing to get a better handle on a warning I am getting from a coxph analysis I am doing.
>> 
>> I am analysing age of onset of dementia *after* the onset of parkinson disease. My data looks like:
>> 
>>   age.park age.dem age.death censor x1 x2   x3   x4
>> 1       76      87        88      0 16 33   E3   E3
>> 2       75      84        84      0 33 36   E3   E3
>> 3       77      81        81      1 NA NA<NA>  <NA>
>> 4       65      65        69      0 NA NA   E4   E4
>> 5       56      76        79      0 NA NA<NA>  <NA>
>> 6       62      72        72      1 NA NA<NA>  <NA>
>> ...
>> 
>> Obviously some individuals (lines 1,2,5) will first develop parkinson, then a few years later, dementia. Some individuals will not develop dementia (lines 3 and 6, where age of death and age of dementia correspond, but the censor variable is 1). Some (more) unluky individuals develop parkinson and dementia at the same time (line 4).
>> 
>> my coxph model looks like
>> 
>> coxph(Surv(age.mot,age.dem, censor) ~ x1 + x2 + x3 + x4, mydata)
>> 
>> and I get the warning:
>> 
>> In Surv(age.mot, age.dem, censor) :
>>   Stop time must be>  start time, NA created
>> 
>> I am almost sure that this is due to the instances where age.park == age.dem, but there is nothing I can really do. So my question:
>> 
>> how do I deal with the instances where age.park == age.dem in order to keep those individuals in the analysis and to get sensible results?
>> 
>> Best wishes
>> 
>> Federico
>> 
>> 
>> 
>> 
>> --
>> Federico C. F. Calboli
>> Department of Epidemiology and Biostatistics
>> Imperial College, St. Mary's Campus
>> Norfolk Place, London W2 1PG
>> 
>> Tel +44 (0)20 75941602   Fax +44 (0)20 75943193
>> 
>> f.calboli [.a.t] imperial.ac.uk
>> f.calboli [.a.t] gmail.com
>> 
>> ______________________________________________
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>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>> 
> 
> -- 
> Dimitris Rizopoulos
> Assistant Professor
> Department of Biostatistics
> Erasmus University Medical Center
> 
> Address: PO Box 2040, 3000 CA Rotterdam, the Netherlands
> Tel: +31/(0)10/7043478
> Fax: +31/(0)10/7043014
> Web: http://www.erasmusmc.nl/biostatistiek/

--
Federico C. F. Calboli
Department of Epidemiology and Biostatistics
Imperial College, St. Mary's Campus
Norfolk Place, London W2 1PG

Tel +44 (0)20 75941602   Fax +44 (0)20 75943193

f.calboli [.a.t] imperial.ac.uk
f.calboli [.a.t] gmail.com