stepComponent(object, component = c("endemic", "epidemic"),
              scope = list(upper = object$formula[[component]]),
              direction = "both", trace = 2, verbose = FALSE, ...)

## S3 method for class 'twinstim'
add1(object, scope, component = c("endemic", "epidemic"), 
    trace = 2, ...)
## S3 method for class 'twinstim'
drop1(object, scope, component = c("endemic", "epidemic"), 
     trace = 2, ...)

data("imdepi", "imdepifit")

## simple baseline model
m0 <- update(imdepifit, epidemic=~1, siaf=NULL)

## AIC-based step-wise backward selection of the endemic component
m0_step <- stepComponent(m0, "endemic", scope=list(lower=~I(start/365-3.5)))
## nothing is dropped from the model