ie.setup {Design} | R Documentation

## Intervening Event Setup

### Description

Creates several new variables which help set up a dataset for modeling with `cph` or `coxph` when there is a single binary time-dependent covariable which turns on at a given time, and stays on. This is typical when analyzing the impact of an intervening event. `ie.setup` creates a `Surv` object using the start time, stop time format. It also creates a binary indicator for the intervening event, and a variable called `subs` that is useful when `attach`-ing a dataframe. `subs` has observation numbers duplicated for subjects having an intervening event, so those subject's baseline covariables (that are not time-dependent) can be duplicated correctly.

### Usage

    ie.setup(failure.time, event, ie.time, break.ties=FALSE)

### Arguments

`failure.time` | a numeric variable containing the event or censoring times for the terminating event
`event` | a binary (0/1) variable specifying whether observations had the terminating event (event=1) or were censored (event=0)
`ie.time` | intervening event times. For subjects having no intervening events, the corresponding values of ie.time must be NA.
`break.ties` | Occasionally intervening events are recorded as happening at exactly the same time as the termination of follow-up for some subjects. The `Surv` function will not allow this. To randomly break the ties by subtracting a random number from such tied intervening event times, specify `break.ties=TRUE`. The random number is uniform between zero and the minimum difference between any two untied `failure.time`s.

### Value

a list with components `S, ie.status, subs, reps`. `S` is a `Surv` object containing start and stop times for intervals of observation, along with event indicators. `ie.status` is one if the intervening event has occurred at the start of the interval, zero otherwise. `subs` is a vector of subscripts that can be used to replicate other variables the same way `S` was replicated. `reps` specifies how many times each original observation was replicated. `S, ie.status, subs` are all the same length (at least the number of rows for `S` is) and are longer than the original `failure.time` vector. `reps` is the same length as the original `failure.time` vector. The `subs` vector is suitable for passing to `validate.lrm` or `calibrate`, which pass this vector under the name `cluster` on to `predab.resample` so that bootstrapping can be done by sampling with replacement from the original subjects rather than from the individual records created by `ie.setup`.

### Author(s)

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

### See Also

`cph`, `coxph`, `Surv`, `cr.setup`, `predab.resample`

### Examples

    failure.time <- c(1 ,   2,   3)
    event        <- c(1 ,   1,   0)
    ie.time      <- c(NA, 1.5, 2.5)

    z <- ie.setup(failure.time, event, ie.time)
    S <- z$S
    S
    ie.status <- z$ie.status
    ie.status
    z$subs
    z$reps
    ## Not run:
    attach(input.data.frame[z$subs,])   #replicates all variables
    f <- cph(S ~ age + sex + ie.status)
    # Instead of duplicating rows of data frame, could do this:
    attach(input.data.frame)
    z <- ie.setup(failure.time, event, ie.time)
    s <- z$subs
    age <- age[s]
    sex <- sex[s]
    f <- cph(S ~ age + sex + ie.status)
    ## End(Not run)

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