我正在学习生存分析的LIFE TABLE,但看到LIFE TABLE中的概率密度时,不知道其结果是如何计算出来的,请教各位,指点指点,谢谢!

期初时间Intrvl Start Time	期初记入数Number Entrng this Intrvl	期内退出数Number Wdrawn During Intrval	历险数Number Exposed to Risk	期间终结数Number of Termnl Events	终结比例Propn Terminating	生存比例Propn Surviving	期末的累积生存比例Cumul Propn Surv at End	期末的累积生存比例的标准误SE of Cumul Surviving	概率密度Probability Densty	概率密度的标准误SE of Probability Densty	风险率Hazard Rate	风险率的标准误SE of Hazard Rate
0	10	1	9.500	0	.00	1.00	1.00	.00	.000	.000	.00	.00
2	9	1	8.500	1	.12	.88	.88	.11	.059	.055	.06	.06
4	7	0	7.000	0	.00	1.00	.88	.11	.000	.000	.00	.00
6	7	2	6.000	1	.17	.83	.74	.16	.074	.068	.09	.09
8	4	0	4.000	0	.00	1.00	.74	.16	.000	.000	.00	.00
10	4	1	3.500	1	.29	.71	.53	.21	.105	.092	.17	.16
12	2	1	1.500	0	.00	1.00	.53	.21	.000	.000	.00	.00
14	1	0	1.000	0	.00	1.00	.53	.21	.000	.000	.00	.00
16	1	1	.500	0	.00	1.00	.53	.21	.000	.000	.00	.00