R: Parametric Survival Model

psm {rms} | R Documentation

## Parametric Survival Model

### Description

`psm` is a modification of Therneau's `survreg` function for fitting the accelerated failure time family of parametric survival models. `psm` uses the `rms` class for automatic `anova`, `fastbw`, `calibrate`, `validate`, and other functions. `Hazard.psm`, `Survival.psm`, `Quantile.psm`, and `Mean.psm` create S functions that evaluate the hazard, survival, quantile, and mean (expected value) functions analytically, as functions of time or probabilities and the linear predictor values.

For the `print` method, format of output is controlled by the user previously running `options(prType="lang")` where `lang` is `"plain"` (the default), `"latex"`, or `"html"`.

The `residuals.psm` function exists mainly to compute normalized (standardized) residuals and to censor them (i.e., return them as `Surv` objects) just as the original failure time variable was censored. These residuals are useful for checking the underlying distributional assumption (see the examples). To get these residuals, the fit must have specified `y=TRUE`. A `lines` method for these residuals automatically draws a curve with the assumed standardized survival distribution. A `survplot` method runs the standardized censored residuals through `npsurv` to get Kaplan-Meier estimates, with optional stratification (automatically grouping a continuous variable into quantiles) and then through `survplot.npsurv` to plot them. Then `lines` is invoked to show the theoretical curve. Other types of residuals are computed by `residuals` using `residuals.survreg`.

### Usage

    psm(formula=formula(data),
        data=parent.frame(), weights,
        subset, na.action=na.delete, dist="weibull",
        init=NULL, scale=0,
        control=survreg.control(),
        parms=NULL,
        model=FALSE, x=FALSE, y=TRUE, time.inc, ...)

    ## S3 method for class 'psm'
    print(x, correlation=FALSE, digits=4, coefs=TRUE,
    title, ...)

    Hazard(object, ...)
    ## S3 method for class 'psm'
    Hazard(object, ...)   # for psm fit
    # E.g. lambda <- Hazard(fit)

    Survival(object, ...)
    ## S3 method for class 'psm'
    Survival(object, ...) # for psm
    # E.g. survival <- Survival(fit)

    ## S3 method for class 'psm'
    Quantile(object, ...) # for psm
    # E.g. quantsurv <- Quantile(fit)

    ## S3 method for class 'psm'
    Mean(object, ...)     # for psm
    # E.g. meant   <- Mean(fit)

    # lambda(times, lp)   # get hazard function at t=times, xbeta=lp
    # survival(times, lp) # survival function at t=times, lp
    # quantsurv(q, lp)    # quantiles of survival time
    # meant(lp)           # mean survival time

    ## S3 method for class 'psm'
    residuals(object, type=c("censored.normalized",
    "response", "deviance", "dfbeta",
    "dfbetas", "working", "ldcase", "ldresp", "ldshape", "matrix"), ...)

    ## S3 method for class 'residuals.psm.censored.normalized'
    survplot(fit, x, g=4, col, main, ...)

    ## S3 method for class 'residuals.psm.censored.normalized'
    lines(x, n=100, lty=1, xlim,
    lwd=3, ...)
    # for type="censored.normalized"

### Arguments

`formula` | an S statistical model formula. Interactions up to third order are supported. The left hand side must be a `Surv` object.
`object` | a fit created by `psm`. For `survplot` with residuals from `psm`, `object` is the result of `residuals.psm`.
`fit` | a fit created by `psm`
`data,subset,weights,dist,scale,init,na.action,control` | see `survreg`.
`parms` | a list of fixed parameters. For the t-distribution this is the degrees of freedom; most of the distributions have no parameters.
`model` | set to `TRUE` to include the model frame in the returned object
`x` | set to `TRUE` to include the design matrix in the object produced by `psm`. For the `survplot` method, `x` is an optional stratification variable (character, numeric, or categorical). For `lines.residuals.psm.censored.normalized`, `x` is the result of `residuals.psm`. For `print` it is the result of `psm`.
`y` | set to `TRUE` to include the `Surv()` matrix
`time.inc` | setting for default time spacing. Used in constructing time axis in `survplot`, and also in make confidence bars. Default is 30 if time variable has `units="Day"`, 1 otherwise, unless maximum follow-up time < 1. Then max time/10 is used as `time.inc`. If `time.inc` is not given and max time/default `time.inc` is > 25, `time.inc` is increased.
`correlation` | set to `TRUE` to print the correlation matrix for parameter estimates
`digits` | number of places to print to the right of the decimal point
`coefs` | specify `coefs=FALSE` to suppress printing the table of model coefficients, standard errors, etc. Specify `coefs=n` to print only the first `n` regression coefficients in the model.
`title` | a character string title to be passed to `prModFit`
`...` | other arguments to fitting routines, or to pass to `survplot` from `survplot.residuals.psm.censored.normalized`. Passed to the generic `lines` function for `lines`.
`times` | a scalar or vector of times for which to evaluate survival probability or hazard
`lp` | a scalar or vector of linear predictor values at which to evaluate survival probability or hazard. If both `times` and `lp` are vectors, they must be of the same length.
`q` | a scalar or vector of probabilities. The default is .5, so just the median survival time is returned. If `q` and `lp` are both vectors, a matrix of quantiles is returned, with rows corresponding to `lp` and columns to `q`.
`type` | type of residual desired. Default is censored normalized residuals, defined as (link(Y) - linear.predictors)/scale parameter, where the link function was usually the log function. See `survreg` for other types.
`n` | number of points to evaluate theoretical standardized survival function for `lines.residuals.psm.censored.normalized`
`lty` | line type for `lines`, default is 1
`xlim` | range of times (or transformed times) for which to evaluate the standardized survival function. Default is range in normalized residuals.
`lwd` | line width for theoretical distribution, default is 3
`g` | number of quantile groups to use for stratifying continuous variables having more than 5 levels
`col` | vector of colors for `survplot` method, corresponding to levels of `x` (must be a scalar if there is no `x`)
`main` | main plot title for `survplot`. If omitted, is the name or label of `x` if `x` is given. Use `main=""` to suppress a title when you specify `x`.

### Details

The object `survreg.distributions` contains definitions of properties of the various survival distributions.
`psm` does not trap singularity errors due to the way `survreg.fit` does matrix inversion. It will trap non-convergence (thus returning `fit$fail=TRUE`) if you give the argument `failure=2` inside the `control` list which is passed to `survreg.fit`. For example, use `f <- psm(S ~ x, control=list(failure=2, maxiter=20))` to allow up to 20 iterations and to set `f$fail=TRUE` in case of non-convergence. This is especially useful in simulation work.

### Value

`psm` returns a fit object with all the information `survreg` would store as well as what `rms` stores and `units` and `time.inc`. `Hazard`, `Survival`, and `Quantile` return S-functions. `residuals.psm` with `type="censored.normalized"` returns a `Surv` object which has a special attribute `"theoretical"` which is used by the `lines` routine. This is the assumed standardized survival function as a function of time or transformed time.

### Author(s)

Frank Harrell
Department of Biostatistics
Vanderbilt University
f.harrell@vanderbilt.edu

### See Also

`rms`, `survreg`, `residuals.survreg`, `survreg.object`, `survreg.distributions`, `pphsm`, `survplot`, `survest`, `Surv`, `na.delete`, `na.detail.response`, `datadist`, `latex.psm`, `GiniMd`, `prModFit`, `ggplot.Predict`, `plot.Predict`

### Examples

    n <- 400
    set.seed(1)
    age <- rnorm(n, 50, 12)
    sex <- factor(sample(c('Female','Male'),n,TRUE))
    dd <- datadist(age,sex)
    options(datadist='dd')
    # Population hazard function:
    h <- .02*exp(.06*(age-50)+.8*(sex=='Female'))
    d.time <- -log(runif(n))/h
    cens <- 15*runif(n)
    death <- ifelse(d.time <= cens,1,0)
    d.time <- pmin(d.time, cens)

    f <- psm(Surv(d.time,death) ~ sex*pol(age,2),
             dist='lognormal')
    # Log-normal model is a bad fit for proportional hazards data

    anova(f)
    fastbw(f)  # if deletes sex while keeping age*sex ignore the result
    f <- update(f, x=TRUE,y=TRUE)       # so can validate, compute certain resids
    validate(f, B=10)      # ordinarily use B=300 or more
    plot(Predict(f, age, sex))   # needs datadist since no explicit age, hosp.
    # Could have used ggplot(Predict(...))
    survplot(f, age=c(20,60))     # needs datadist since hospital not set here
    # latex(f)

    S <- Survival(f)
    plot(f$linear.predictors, S(6, f$linear.predictors),
         xlab=expression(X*hat(beta)),
         ylab=expression(S(6,X*hat(beta))))
    # plots 6-month survival as a function of linear predictor (X*Beta hat)

    times <- seq(0,24,by=.25)
    plot(times, S(times,0), type='l')   # plots survival curve at X*Beta hat=0
    lam <- Hazard(f)
    plot(times, lam(times,0), type='l') # similarly for hazard function

    med <- Quantile(f)        # new function defaults to computing median only
    lp <- seq(-3, 5, by=.1)
    plot(lp, med(lp=lp), ylab="Median Survival Time")
    med(c(.25,.5), f$linear.predictors)
                              # prints matrix with 2 columns

    # fit a model with no predictors
    f <- psm(Surv(d.time,death) ~ 1, dist="weibull")
    f
    pphsm(f)          # print proportional hazards form
    g <- survest(f)
    plot(g$time, g$surv, xlab='Time', type='l',
         ylab=expression(S(t)))

    f <- psm(Surv(d.time,death) ~ age,
             dist="loglogistic", y=TRUE)
    r <- resid(f, 'cens') # note abbreviation
    survplot(npsurv(r ~ 1), conf='none')
                          # plot Kaplan-Meier estimate of
                          # survival function of standardized residuals
    survplot(npsurv(r ~ cut2(age, g=2)), conf='none')
                          # both strata should be n(0,1)
    lines(r)              # add theoretical survival function
    #More simply:
    survplot(r, age, g=2)

    options(datadist=NULL)

[Package rms version 5.1-1 Index]