Furthermore, the variables of area and thicknesses were treated as quantitative variables to measure the closeness between data points, and it was found that the completion of missing values with zero yielded better results than using the median. It is known that the completion of missing values with the mean is not ideal due to the induction of bias , and using the median probably produced similar outcomes. Hence, it is suggested that zero completion is preferable to median completion. Other predictive functions of GBDT and NN afforded lower prediction performance than RF, identifying RF was the best (Fig. ).