R/compute_qic.r

In SLTCA: Scalable and Robust Latent Trajectory Class Analysis

ic <- function(geefit,Y_dist,yy){

  #require(geepack)
  requireNamespace("geepack")
  #weights(geefit) gives posterior membership probabilities tau
  #geefit$geese$gamma is the estimated scale parameter

  if(Y_dist == 'normal'){
    qlik = -0.5*sum(weights(geefit)*(yy-fitted(geefit))*(yy-fitted(geefit)))/geefit$geese$gamma
    v = geefit$geese$gamma
  }else if (Y_dist == 'bin'){
    #yy = 1-(yy-1)
    qlik = sum(weights(geefit)*(yy*log(fitted(geefit)/(1-fitted(geefit))) + log(1 - fitted(geefit))))/geefit$geese$gamma
    v = geefit$geese$gamma*fitted(geefit)*(1-fitted(geefit))
  }else if (Y_dist == 'poi'){
    qlik = sum(weights(geefit)*(yy*log(fitted(geefit)) - fitted(geefit) - log(factorial(yy))))/geefit$geese$gamma
    v = geefit$geese$gamma*fitted(geefit)
  }

  eqlik = qlik - 0.5*sum(weights(geefit)*log(v))

  ceeqic = -2*eqlik

  ceeqic
}