Evaluation of Imputation Models Based on the Enhancement to Yield Forecasting

Abstract

Market price and yield forecasting models for Fresh Produce (FP) are crucial to protect retailers and consumers from overpriced FP. However, utilizing the data for forecasting is obstructed by the occurrence of missing values. Therefore, it is imperative to impute the encountered missing instances to enable effective forecasting. Most of the work found in literature tackles imputation of missing values when they are randomly scattered in the dataset while very little work is found tackling both: consecutive occurrence of missing data, i.e. missing data chunks, as well as those randomly missing. In this work, the data used for forecasting has missing values in chunks as well as at random points. Therefore, various comprehensive imputation models are used to impute both random as well as chunks of missing values. Since the imputed time series are incomplete, the only way to evaluate those imputation models is to analyze their effect on forecasting performance. The ensemble of two compound deep learning (DL) models, namely Attention Convolutional Neural Networks Long Short Term Memory (Att-CNN-LSTM) and SeriesNet with Gated Recurrent Unit (GRU), is used for forecasting. For imputation, three DL models are tested: The Ensemble imputation model which is a Voting Regressor of two DL submodels, Residual GRU and LSTM-Deep-GRU. Another deep learning imputation model is used which is a Transfer Learning (TL) model. Finally, a Hybrid model of both DL models is designed to take the pros of each of its integrated models by using the Ensemble model in case of random missing data and the Transfer Learning model in case of missing data chunks. It is observed that, in general, imputing the missing values improves the forecasting result as compared to eliminating the instances with missing values. The Hybrid model improves the overall forecasting performance by up to 60% compared to the case of using the second-best Transfer Learning model and around 64% as compared to the case of imputation using the Ensemble model.