“…It requires only four recent sample data points to achieve reliable and acceptable prediction accuracy (Wen, 2004;Wang and Hsu, 2008), and has been widely applied to management, economics and engineering (Feng et al, 2012;Li et al, 2012;Pi et al, 2010;Lee and Tong, 2011;Mao and Chirwa, 2006;Hu et al, 2015;Hu, 2013;Tsaur and Liao, 2007;Cui et al, 2013;Wei et al, 2015). To improve prediction accuracy of the original GM(1,1) model, several improved versions have been proposed, such as an improved grey model with convolution integral GMC(1, n) (Wang and Hao, 2016), a self-adaptive intelligence model (Zeng et al, 2016), Rolling-ALO-GM(1, 1) model for annual power load forecasting (Zhao and Guo, 2016), PGM(1,1) using particle swarm optimization to determine the development coefficient (Li et al, 2016) and grey wave forecasting that established GM(1,1) models on the basis of qualified contour time sequences (Chen et al, 2016).…”