In order to test the hypotheses, unnecessary columns are dropped off and only “birth year” and “date” are left. Two sample group are split based on their birth year: users who born after 1980 (inclusing 1980) belongs to the young group, while users who born before 1980 is assigned to other age groups. By applying groupby() and count() function, finally the number of people in different group in each day is got as Fig. 3 shown.