a dummy variable is a binary variable that IS I if a happens D lO if a happens EXample: D ∫1,解放后 「1, student D 0解放前0, teacher 2t≥t t=1979 o. t< t 2021/2/202021/2/20 6 A dummy variable is a binary variable, that is, Example: 1 if A happens 0 if A happens D  =   1, 0, D  =   解放后 解放前 1, student 0, teacher D  =   * * * 1, , 1979 0, t t t D t t t   = =   