\HeaderA{survexp.fit}{Compute Expected Survival}{survexp.fit}
\keyword{survival}{survexp.fit}
\begin{Description}\relax
Compute expected survival times.
\end{Description}
\begin{Usage}
\begin{verbatim}
survexp.fit(x, y, times, death, ratetable)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{x}] a matrix. The first column contains the group, 
an integer value that divides the subjects into subsets. 
Remaining columns must match the dimensions of the \code{ratetable}, 
in the correct order. 

\item[\code{y}] the follow up time for each subject. 

\item[\code{times}] the vector of times at which a result will be computed. 

\item[\code{death}] a logical value, if \code{TRUE} the conditional survival is computed, 
if \code{FALSE} the cohort survival is computed. See
\code{\LinkA{survexp}{survexp}} for more details.

\item[\code{ratetable}] a rate table, such as \code{survexp.uswhite}. 

\end{ldescription}
\end{Arguments}
\begin{Details}\relax
For conditional survival \code{y} must be the time of last follow-up or death for 
each subject. 
For cohort survival it must be the potential censoring time for 
each subject, ignoring death. 

For an exact estimate \code{times} should be a superset of \code{y}, so that each 
subject at risk is at risk for the entire sub-interval of time. 
For a large data set, however, this can use an inordinate amount of 
storage and/or compute time.  If the \code{times} spacing is more coarse than 
this, an actuarial approximation is used which should, however, be extremely 
accurate as long as all of the returned values are \textgreater{} .99. 

For a subgroup of size 1 and \code{times} \textgreater{} \code{y}, 
the conditional method reduces to exp(-h) where 
h is the expected cumulative hazard for the subject over his/her 
observation time.  This is used to compute individual expected survival.
\end{Details}
\begin{Value}
A list containing the number of subjects and the expected survival(s) 
at each time point. 
If there are multiple groups, these will be 
matrices with one column per group.
\end{Value}
\begin{Section}{Warning}
Most users will call the higher level routine \code{survexp}. 
Consequently, this function has very few error checks on its input arguments.
\end{Section}
\begin{SeeAlso}\relax
\code{\LinkA{survexp}{survexp}},  \code{\LinkA{survexp.us}{survexp.us}}.
\end{SeeAlso}

