wald.strata {JM}

Wald Test for Stratification Factors

Description

It performs a Wald test to test the hypothesis of equal spline coefficients among strata in the approximation of baseline risk function.

Usage

wald.strata(fit)

Arguments

fit

an object of class jointModel with method = "spline-PH-GH" and with a strata specification in the survival part.

Value

an object of class wald.strata with components:

alternative

a character string naming the alternative.

Result

a numeric matrix with the results of the Wald test.

Note

This test is valid when the same knots have been used across strata.

Author(s)

Dimitris Rizopoulos [e-mail]

References

Rizopoulos, D. (2012) Joint Models for Longitudinal and Time-to-Event Data: with Applications in R. Boca Raton: Chapman and Hall/CRC.

Examples

## Not run: 
fitLME <- lme(log(serBilir) ~ drug * year - drug, random = ~ year | id, 
    data = pbc2)
fitSURV <- coxph(Surv(years, status2) ~ drug + strata(hepatomegaly), 
    data = pbc2.id, x = TRUE)
fit.pbc <- jointModel(fitLME, fitSURV, timeVar = "year", method = "spline-PH-aGH")
wald.strata(fit.pbc)

## End(Not run)