“…The functional form could be linear [23,25,26,31,33,43,47,48,51,53], semi-log [20,24,[27][28][29][30][34][35][36][37]41,42,44,46,49,50,52], or log-linear (log-log) [6,21,22,39,45,55]. Temporal dimension could be incorporated in the model by adding a dummy variable of year [25,31].…”