Histograms and relevant statistical results of artificial data sets. From left to right: the four columns, (a)-(e), (f)-(j), (k)-(p) and (q)-(u), show results of data sets with f
of 250, 360, 500 and 1000 Hz, respectively. For each data set, from top to bottom: the first four rows show results of four groups, including groups ❶, ❷, ❸ and ➍, respectively. Four curves in each inset in the last row, which contains (e), (j), (p) and (u), correspond to four histograms in the same column and ordered by the legends, respectively.