In the last few years, there have been many methodological and theoretical advances in the random forests approach. Some methodological developments and extensions include case-specific random forests , multivariate random forests , quantile regression forests , random survival forests , enriched random forests for microarry data  and predictor augmentation in random forests  among others. For theoretical developments, the statistical and asymptotic properties of random forests have been intensively investigated. Advances have been made in the areas such as consistency  , variable selection  and the construction of confidence intervals . Although RF methodology has proven itself to be a reliable predictive approach in many application areas , there are some cases where random forests may suffer. First, as a fully nonparametric predictive algorithm, random forests may not efficiently incorporate known relationships between the response and the predictors. Second, random forests may fail in extrapolation problems where predictions are required at points out of the domain of the training dataset. For regression problems, a random forest prediction is an average of the predictions produced by the trees in the forest.