TY - JOUR A1 - Jain, Brijnesh T1 - Revisiting inaccuracies of time series averaging under dynamic time warping JF - Pattern Recognition Letters N2 - This article revisits an analysis on (in)accuracies of time series averaging under dynamic time warping (dtw) conducted by Niennattrakul and Ratanamahatana [16]. They proposed a correctness-criterion for dtw-averages and postulated that dtw-averages can drift out of the cluster of time series to be averaged. They claimed that dtw-averages are inaccurate if they violate the correctness-criterion or suffer from the drift-out phenomenon. Furthermore, they conjectured that such inaccuracies are caused by the lack of triangle inequality. In this article, we show that a rectified version of the correctness-criterion is unsatisfiable and that the concept of drift-out is geometrically and operationally inconclusive. Satisfying the triangle inequality is insufficient to achieve correctness and unnecessary to overcome the drift-out phenomenon. We place the concept of drift-out on a principled basis and show that Fréchet means never drift out. The adjusted drift-out is a way to test to which extent an approximated dtw-average is coherent. Empirical results show that approximations obtained by the state-of-the-art averaging methods are incoherent in over a third of all cases. KW - k-means KW - Time series averaging KW - Dynamic time warping KW - Time series Y1 - 2019 U6 - https://doi.org/10.1016/j.patrec.2019.05.022 VL - 125 IS - July SP - 418 EP - 424 PB - Elsevier ER -