“…In particular, he distinguishes three major categories of approaches to time series clustering: 1) raw-data-based approaches, in which the series compared are considered as normally sampled at the same interval; 2) features-based approaches, in which the series are compared using some selected features; 3) model-based methods, where the time series are considered similar when the models characterizing them are similar. The approach proposed in this work belongs to the third category; in particular it follows the tradition of AR processes to capture the similarity among time series, as in Piccolo (1990), Maharaj (1996Maharaj ( , 1999Maharaj ( , 2000, Xiong and Yeung (2002) (see Piccolo, 2007, and Corduas and Piccolo, 2008, for a review). Most of these studies are devoted to capturing the structure of the mean of the process hypothesized as generator of the data, whereas little attention was put on the variance.…”