updateBeta: Function for updating the coefficient(s) for covariate(s)

Description

The function updates the partial likelihood estimate of the coefficient(s) for covariate(s) (i.e. beta) by solving the pseudo-score equation of the stratified proportional hazards model with dynamic treatment regimes (DTRs) as strata proposed in Tang and Wahed (2013) [Epub ahead of print]. The Newton-Raphson method is used for computation.

Usage

updateBeta(beta, V, U, delta, w11, w12, w21, w22)

Arguments

beta

current estimate of the coefficient(s) for covariate(s)

covariates included in the model. The function allows for one covariate or more than one covariates

observed survival time, U is death time if delta=1, and U is censoring time if delta=0

delta

censoring indicator, delta=1 for died, and delta=0 for censored

w11

weights for dynamic treatment regime A1B1

w12

weights for dynamic treatment regime A1B2

w21

weights for dynamic treatment regime A2B1

w22

weights for dynamic treatment regime A2B2

Value

The function returns an updated estimate of the coefficient(s) for covariate(s).
beta_upan updated estimate of the coefficient(s) for covariate(s)

Details

This function is for internal use only and is not to be called by the user. In sequentially randomized designs, there could be more than two therapies available at each stage. For simplicity, and to maintain similarity to the most common sequentially randomized clinical trials, a simple two-stage randomization design allowing two treatment options at each stage is used in the current version of the package. In detail, patients are initially randomized to either A1 or A2 at the first stage. Based on their response status, they are then randomized to either B1 or B2 at the second stage. Therefore, there are a total of four DTRs: A1B1, A1B2, A2B1, and A2B2.

References

Tang X, Wahed AS: Cumulative hazard ratio estimation for treatment regimes in sequentially randomized clinical trials. Statistics in Biosciences, 2013 [Epub ahead of print]