R/truePrevBinom.R

In prevalence: Tools for Prevalence Assessment Studies

truePrevBinom <-
function(x, n, Se, Sp, prior,
         nchains, burnin, update, verbose){

  ## create model
  model <- character()
  model[1] <- "model {"
  model[2] <- "x ~ dbin(AP, n)"
  model[3] <- "AP <- SE * TP + (1 - SP) * (1 - TP)"

  model <- c(model, writeSeSp("SE", Se))
  model <- c(model, writeSeSp("SP", Sp))

  model <-
    c(model,
      paste0("TP ~ dbeta(", prior[1], ", ", prior[2], ")"))

  model <- c(model, "}")

  class(model) <- "prevModel"

  ## create data
  data <- list(x = x, n = n)

  ## generate inits
  inits <- NULL

  ## get results!
  if (verbose) cat("JAGS progress:\n\n")

  JAGSout <- R2JAGS(model = model, data = data, inits = inits,
                    nchains = nchains, burnin = burnin, update = update,
                    nodes = c("TP", "SE", "SP"), verbose = verbose)

  mcmc.list <- JAGSout$mcmc.list
  class(mcmc.list) <- c("list", "mcmc.list")

  nodes <- colnames(mcmc.list[[1]])                      # extract node names
  mcmc.list_list <- list()                               # initiate list
  for (i in seq_along(nodes))                            # assign nodes
    mcmc.list_list[[i]] <- mcmc.list[, i]
  names(mcmc.list_list) <- nodes                         # assign node names
  mcmc.list_list <- mcmc.list_list[c("TP", "SE", "SP")]  # reorder elements

  ## define diagnostics
  # deviance information criterion
  DIC <- JAGSout$dic

  # brooks-gelman-rubin diagnostic
  # exclude fixed nodes
  exclude <- which(apply(mcmc.list[[1]], 2, sd) == 0)
  if (length(exclude) > 0) {
    BGR <- gelman.diag(mcmc.list[, -exclude])
  } else {
    BGR <- gelman.diag(mcmc.list)
  }

  ## create new 'prev' object
  out <-
    new("prev",
        par = list(x = x, n = n, SE = Se, SP = Sp, prior = prior,
                   nchains = nchains, burnin = burnin, update = update,
                   inits = inits),
        model = model,
        mcmc = mcmc.list_list,
        diagnostics = list(DIC = DIC,
                           BGR = BGR))

  return(out)
}