R: Quantiles from a survfit object

quantile.survfit {survival} | R Documentation

## Quantiles from a survfit object

### Description

Retrieve quantiles and confidence intervals for them from a survfit object.

### Usage

    ## S3 method for class 'survfit'
    quantile(x, probs = c(0.25, 0.5, 0.75), conf.int = TRUE,
    ...)

### Arguments

`x` | a result of the survfit function
`probs` | numeric vector of probabilities with values in [0,1].
`conf.int` | should lower and upper confidence limits be returned?
`...` | optional arguments for other methods

### Details

The kth quantile for a survival curve S(t) is the location at which a horizontal line at height 1-k intersects the plot of S(t). Since S(t) is a step function, it is possible for the curve to have a horizontal segment at exactly 1-k, in which case the midpoint of the horizontal segment is returned. This mirrors the standard behavior of the median when data is uncensored. If the survival curve does not fall to 1-k, then that quantile is undefined.

Confidence limits for the values are based on the intersection of the horizontal line at 1-k with the upper and lower limits for the survival curve. Hence confidence limits use the same p-value as was in effect when the curve was created, and will differ depending on the `conf.type` option of `survfit`. If the survival curves have no confidence bands, confidence limits for the quantiles are not available.

### Value

The quantiles will be a vector if the `survfit` object contains only a single curve, otherwise it will be a matrix or array. In this latter case the second dimension will index the quantiles.

If confidence limits are requested, then result will list with components `quantile`, `lower`, and `upper`, otherwise the vector or matrix of quantiles.

### Author(s)

Terry Therneau

### See Also

`survfit`, `print.survfit`, `qsurvreg`

### Examples

    fit <- survfit(Surv(time, status) ~ ph.ecog, data=lung)
    quantile(fit)

[Package survival version 2.36-14 Index]