Sneh Ringwala

Intermediate Epidemiology

Week 2

A. Starting N = 20; Maximum duration of follow up = 24 months

MonthsOutcomeProbability of DeathProbability of SurvivalSurvival Function

2Death0.05(20-1)/20 = 0.9500.95

4Censored

7Censored

8Death0.06(17-1)/17 = 0.9410.95 * 0.941 = 0.894

12Censored

15Death0.067(15-1)/15 = 0.9330.893 * 0.933 = 0.834

17Death0.071(14-1)/14 = 0.9290.83 * 0.929 = 0.775

19Death0.077(13-1)/13 = 0.9230.771 * 0.923 = 0.715

20Censored

23Death0.091(11-1)/11 = 0.9090.712 * 0.909 = 0.650

B. 0.650 or 65%

C. Attached

D. 1 - (6 participant deaths / 20 participants) = 0.7 or 70%

E. The survival function accounts for duration of follow-up.

F.

Total months of observation = 2 + 4 + 7 + 8 + 12 + 15 + 17 + 19 + 20 + 23 + (10 * 24) = 367 months or 30.58 years

Deaths / Time = 6 / 30.58 years * 100 years = 19.6 death rate per 100 person years

G.

Year One

Total months of observation = 2 + 4 + 7 + 8 + (12 * 16) = 213 months or 17.75 years

Deaths / Time = 2 / 17.75 years * 100 years = 11.3 death rate per 100 person years

Year TwoTotal months of observation = 367 months 213 months = 154 months or 12.83 years

Deaths / Time = 4 / 12.83 years * 100 years = 31.2 death rate per 100 person years

H. The year one and year two rates are different. Reporting them separately may provide insight that the combined two-year rate does not provide.

I. Survival analysis assumes that the event rate for the censored participants is the same as the participants that were followed for the duration of the study.

J.

Proportion dying = 6 / 20 = 0.3

Odds of death = 6 / 14 = 0.43

K. The numbers are different because the event rate is high in these twenty participants.