Historically, the two rate constants in the SIR model are combined to a new parameter called the reproduction number. Three different forms of reproduction number are examined in this lab, namely the time-dependent reproduction number Rt, the time-dependent effective reproduction number Re, and the basic reproduction number, R0 (Equations 1-2). The time-dependent reproduction number, Rt, reflects the infectivity of the virus and the social interaction frequency of the society and is defined: