Taking this as basic point, survival rate at previous period was that the survival rate at certain period divided by retention rate according to probability principle of multiplication.

• 以此为基点,根据乘法概率法则,将某一年龄段的生存率除以留存率可得前一年龄段的生存率,同理可反推出平均年龄以下各年龄段的生存率。