再生性
X i ∼ Po ( λ i ) ( i = 1 , 2 ) ⟶ X 1 + X 2 ∼ Po ( λ 1 + λ 2 ) {\displaystyle X_{i}\sim {\mbox{Po}}(\lambda _{i})\ (i=1,2)\ \longrightarrow X_{1}+X_{2}\sim {\mbox{Po}}(\lambda _{1}+\lambda _{2})}