[R] Incidence estimated from Kaplan-Meier

[Frank E Harrell Jr]

Nguyen Dinh Nguyen wrote:
> Dear all,
> 
> I have a stat question that may not be related to R, but I would like to
> have your advice.
> 
>  
> 
> I have just read a medical paper in which the authors report the 1-p (where
> p is the cumulative survival probability from the Kaplan Meier curve) as
> incidence of disease.  
> 
>  
> 
> Specifically, the study followed ~12000 women on drug A and ~20000 women on
> drug B for 12 months.  During that period 29 women on drug A and 80 on drug
> B had the disease.  The incidence of disease for A and B was 0.24% and 0.30%
> respectively.  However, instead of reporting these numbers, they report the
> 1-p figure which was 0.3% for A and 0.6% for B. 
> 
>  
> 
> So, the incidence from 1-p was substantially higher than the actual
> incidence.  My question is: is it appropriate to use 1-p estimated from
> Kaplan-Meier as the incidence of disease?  If not, why not? 
> 
>  
> 
> Regards,
> 
> Nguyen

Yes it's appropriate, and it makes you state the cumulative incidence by 
time t rather than leaving time unspecified.  In your example it is 
likely that all women weren't followed completely, so simple incidences 
are not appropriate to compute because the denominator is not constant.

Frank

> 
>  
> 
> ____________________________ 
> Nguyen Dinh Nguyen, 
> 
> Bone and Mineral Research Program 
> Garvan Institute of Medical Research 
> St Vincent's Hospital 
> 384 Victoria Street, Darlinghurst 
> Sydney, NSW 2010 
> Australia 
> Tel; 61-2-9295 8274 
> Fax: 61-2-9295 8241 
> E-mail: n.nguyen at garvan.org.au 
> 
>  
> 
> 
> 	[[alternative HTML version deleted]]
> 
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-- 
Frank E Harrell Jr   Professor and Chair           School of Medicine
                      Department of Biostatistics   Vanderbilt University