test_elife {longevity}

Likelihood ratio test for covariates

Description

This function fits separate models for each distinct value of the factor covariate and computes a likelihood ratio test to test whether there are significant differences between groups.

Usage

test_elife(
  time,
  time2 = NULL,
  event = NULL,
  covariate,
  thresh = 0,
  ltrunc = NULL,
  rtrunc = NULL,
  type = c("right", "left", "interval", "interval2"),
  family = c("exp", "gp", "weibull", "gomp", "gompmake", "extgp", "extweibull", "perks",
    "perksmake", "beard", "beardmake"),
  weights = rep(1, length(time)),
  arguments = NULL,
  ...
)

Arguments

time

excess time of the event of follow-up time, depending on the value of event

time2

ending excess time of the interval for interval censored data only.

event

status indicator, normally 0=alive, 1=dead. Other choices are TRUE/FALSE (TRUE for death). For interval censored data, the status indicator is 0=right censored, 1=event at time, 2=left censored, 3=interval censored. Although unusual, the event indicator can be omitted, in which case all subjects are assumed to have experienced an event.

covariate

vector of factors, logical or integer whose distinct values define groups

thresh

vector of thresholds

ltrunc

lower truncation limit, default to NULL

rtrunc

upper truncation limit, default to NULL

type

character string specifying the type of censoring. Possible values are "right", "left", "interval", "interval2".

family

string; choice of parametric family

weights

weights for observations

arguments

a named list specifying default arguments of the function that are common to all elife calls

...

additional arguments for optimization, currently ignored.

Value

a list with elements

• stat likelihood ratio statistic

• df degrees of freedom

• pval the p-value obtained from the asymptotic chi-square approximation.

Examples

test <- with(subset(dutch, ndays > 39082),
 test_elife(
 time = ndays,
 thresh = 39082L,
 covariate = gender,
 ltrunc = ltrunc,
 rtrunc = rtrunc,
 family = "exp"))
 test