Fit a model for the mediator given the treatment and covariates.
lm is called if mreg = "linear". glm is called with family = binomial() if mreg = "logistic".
fit_mreg(mreg, data, avar, mvar, cvar, emm_ac_mreg = NULL)
mreg: A character vector of length 1. Mediator regression type: "linear" or "logistic".data: Data frame containing the following relevant variables.avar: A character vector of length 1. Treatment variable name.mvar: A character vector of length 1. Mediator variable name.cvar: A character vector of length > 0. Covariate names. Use NULL if there is no covariate. However, this is a highly suspicious situation. Even if avar is randomized, mvar is not. Thus, there are usually some confounder(s) to account for the common cause structure (confounding) between mvar and yvar.emm_ac_mreg: A character vector of length > 0. Effect modifiers names. The covariate vector in treatment-covariate product term in the mediator model.A regression object of class lm (linear) or glm (logistic)