drcount {precmed}

Doubly robust estimator of the average treatment effect for count data

Description

Doubly robust estimator of the average treatment effect between two treatments, which is the rate ratio of treatment 1 over treatment 0 for count outcomes.

Usage

drcount(
  y,
  trt,
  x.cate,
  x.ps,
  time,
  ps.method = "glm",
  minPS = 0.01,
  maxPS = 0.99,
  interactions = TRUE
)

Arguments

y

A numeric vector of size n with each element representing the observed count outcome for each subject.

trt

A numeric vector (in 0, 1) of size n with each element representing the treatment received for each subject.

x.cate

A numeric matrix of dimension n by p.cate with each column representing each baseline covariate specified in the outcome model for all subjects.

x.ps

A numeric matrix of dimension n by p.ps + 1 with a leading column of 1 as the intercept and each remaining column representing each baseline covariate specified in the propensity score model for all subjects.

time

A numeric vector of size n with each element representing the log-transformed person-years of follow-up for each subject.

ps.method

A character value for the method to estimate the propensity score. Allowed values include one of: 'glm' for logistic regression with main effects only (default), or 'lasso' for a logistic regression with main effects and LASSO penalization on two-way interactions (added to the model if interactions are not specified in ps.model). Relevant only when ps.model has more than one variable.

minPS

A numerical value between 0 and 1 below which estimated propensity scores should be truncated. Default is 0.01.

maxPS

A numerical value between 0 and 1 above which estimated propensity scores should be truncated. Must be strictly greater than minPS. Default is 0.99.

interactions

A logical value indicating whether the outcome model should allow for treatment-covariate interaction by x. If TRUE, interactions will be assumed only if at least 10 patients received each treatment option. Default is TRUE.

Value

Return a list of 4 elements:

• log.rate.ratio: A numeric value of the estimated log rate ratio.

• rate0: A numeric value of the estimated rate in the group trt=0.

• rate1: A numeric value of the estimated rate in the group trt=1.