survobrien {survival}R Documentation

O'Brien's Test for Association of a Single Variable with Survival


Peter O'Brien's test for association of a single variable with survival This test is proposed in Biometrics, June 1978.


survobrien(formula, data)


formula a valid formula for a cox model, without time dependent covariates.
data a data frame.


a new data frame. The original time and status variables are removed, and have been replaced with start, stop, and event. If a predictor variable is a factor or is protected with I(), it is retained as is. Other predictor variables have been replaced with time-dependent logit scores.
Because of the time dependent variables, the new data frame will have many more rows that the original data, approximately #rows * #deaths /2.


A time-dependent cox model can now be fit to the new data. The univariate statistic, as originally proposed, is equivalent to single variable score tests from the time-dependent model. This equivalence is the rationale for using the time dependent model as a multivariate extension of the original paper.

In O'Brien's method, the x variables are re-ranked at each death time. A simpler method, proposed by Prentice, ranks the data only once at the start. The results are usually similar.


O'Brien, Peter, "A Nonparametric Test for Association with Censored Data", Biometrics 34: 243-250, 1978.

See Also



xx <- survobrien(Surv(futime, fustat) ~ age + factor(rx) + I(,
coxph(Surv(start, stop, event) ~ age, data=xx)
coxph(Surv(start, stop, event) ~ age + rx +, data=xx)

[Package survival version 2.31 Index]