[R] Fitting a survival curve

[Ben Bolker]

Richard Pitman <richard.pitman3 <at> btopenworld.com> writes:

> 
> I am new to R and am trying to fit a survival curve with a weibull
> hazard function to a set of data giving the probability of survival to
> age x, given the year of birth, in the form:
> 
> Probability of survival:
> 			Birth year
> 		1980	1981	...	2003
> 	.2	0.90	0.89	...	0.87
> 	1	0.80	0.81	...	0.79
> age	2	0.75	0.74	...	0.73
> 	3	0.70	0.69	...	0.68
> 	5	0.50	0.49	...	0.43
> 	10	0.30	0.31	...	0.26
> 
> I would like to be able to fit a curve to each birth cohort, extrapolate
> the curve a few years and be able to create a plot of the survival
> curves.
> 


  You don't have enough data for a standard survival analysis,
which is based on individual-level survival times.  (You don't
even know the total cohort size, which you would need to know
to fit a binomial model.)  However, you can compute the _expected_
probabilities of survival to age a using dweibull(a) [or,
since your categories are fairly coarse, pweibull(a2)-pweibull(a1)].
As a starting point, you could try a least-squares fit through
the data -- again, this is not quite right, but in the
absence of information about sample size it's a little hard
to know how to weight the different points.

  Hope that helps.
   Ben Bolker