Dashed and dotted curves represent two individual Gaussian functions. As shown in Fig. 1, the distribution of COL as a whole is bimodal, which is well represented by the double Gaussian function having maxima of 11 and 20. As a goodness of the
fit, we consider the quantity v2 corresponding to a sum of N squares of (yiy0), where yi and y0 are the observed data and the expected value in the distribution of COL, respectively.