Statistics of the logarithmic molecular abundance ratio of M1 and M2 for the gas-phase species and grain species at the three different evolutionary times. Panel a shows modeling parameters with a grain temperature T_d = 10 K and E_dif/E_des = 0.5, and panel b shows T_d = 20 K and E_dif/E_des = 0.3. X_M1 and X_M2 represent the abundance of a species in models M1 and M2, respectively. The solid lines represent the relative percentage of each bin with respect to the total number of the gas-phase or grain species averaged over the three different times. The width of each bin is 0.3.