exportPattern("^[[:alpha:]]+")
  importFrom("grDevices", "dev.list", "dev.off", "graphics.off", "pdf")
  importFrom("graphics", "axis", "lines", "par", "plot", "polygon",
             "text", "title")
  importFrom("stats", "as.formula")
  importFrom("survival", "coxph", "coxph.detail")
  importFrom("stats", "pchisq")
