Deck 6: The Natural History of Disease: Ways of Expressing Prognosis

Question 1

The following table describes the survival of patients treated from disease X from 2015 to 2017 followed for 3 years (assuming no loss to follow-up).What was the probability of surviving the third year?

A) 0.29
B) 0.33
C) 0.61
D) 0.67
E) 0.71

Answer 1

E
Please see calculations for each year:
P₁ = Probability of surviving the first year = 150/225 = 0.67,or 67%
P₂ = Probability of surviving the second year = 60/(150-52) = 0.61,or 61%
P₃ = Probability of surviving the third year = 30/(60-18) = 0.71,or 71%

Question 2

What is the cumulative probability of surviving to the end of the 4-year follow-up period? Use the following table to answer the question. Survival of Patients With Metastatic Cancer Z Following Diagnosis

A) 0.06
B) 0.11
C) 0.54
D) 0.67
E) 0.89

Answer 2

A
The cumulative probability of surviving (Pₓ) is a multiplication of the probability of surviving each interval.For detailed calculation,see the following table.

Question 3

What is the most important assumption in this type of analysis? Use the following table to answer the question. Survival of Patients With Metastatic Cancer Z Following Diagnosis

A) There has been no secular (temporal) change in the effectiveness of treatment or in survivorship over calendar time.
B) The effect of treatment has improved during the period of the study.
C) The survival experience of people who are lost to follow-up is better than the experience of those who are followed up.
D) The survival experience of people who are lost to follow-up is worse than the experience of those who are followed up.
E) An equal number of men and women enrolled each year.

Answer 3

A
There are two important assumptions made in using life-time table.The first one is that there has been no improvement on treatment effect.The second one is that the survival experience of people who are lost to follow-up is same as the experience of those who are followed up."The effect of treatment has improved during the period of the study" is not correct.The treatment effect should be the same during the period of the study."The survival experience of people who are lost to follow-up is better than the experience of those who are followed up" and "The survival experience of people who are lost to follow-up is worse than the experience of those who are followed up" are not correct.The survival experience of people who are lost to follow-up should be the same as the experience of those who are followed up."An equal number of men and women enrolled each year" is not correct.An equal number of men and women enrolled in the study does not have any meaning in life-time table.

Question 4

Which of the following illustrates a violation to one of the assumptions made when using the Kaplan-Meier method?

A) Some patients who dropped out of the study have a similar probability of survival as those who remained in it.
B) Patients present the outcome at different time intervals.
C) An event of interest different from death is studied.
D) There is a significant improvement in the treatment of the condition being studied in the middle of the duration of the study.
E) The median survival time is longer than the duration of the study.

Question 5

What is the probability of dying in those who did not die during the 25- to 36-month interval? Use the following table to answer the question. Survival of Patients With Metastatic Cancer Z Following Diagnosis
$\begin{array}{|l|l|l|l|l|l|l|l|}\hline \begin{array}{l}\text { Interval } \\\text { since } \\\text { beginning } \\\text { treatment } \\\text { (months) }\end{array} & \begin{array}{l}\text { Alive at } \\\text { beginning } \\\text { of } \\\text { interval }\end{array} & \begin{array}{l}\text { Died } \\\text { during } \\\text { interva } \\1\end{array} & \begin{array}{l}\text { Withdre } \\\text { w during } \\\text { interval }\end{array} & \begin{array}{l}\text { Effective } \\\text { number } \\\text { exposed } \\\text { to risk of } \\\text { dying }\end{array} & \begin{array}{l}\text { Proporti } \\\text { on who } \\\text { died } \\\text { during } \\\text { interval }\end{array} & \begin{array}{l}\text { Proportion } \\\text { who did not } \\\text { die during } \\\text { interval }\end{array} & \begin{array}{l}\text { Cumulative } \\\text { proportion } \\\text { who } \\\text { survived } \\\text { from } \\\text { enrollment } \\\text { to end of } \\\text { interval }\end{array} \\\hline x & I_{x} & d_{x} & W_{x} & I_{x}^{\prime} & q_{x} & p_{x} & P_{x} \\\hline 1-12 & 200 & 10 & 40 & & & & \\\hline 13-24 & 150 & 20 & 30 & & & & \\\hline 25-36 & 100 & 30 & 20 & & & & \\\hline 37-48 & 50 & 40 & 10 & & & & \\\hline\end{array}$

A) 0.30
B) 0.33
C) 0.38
D) 0.67
E) 0.70

Question 6

The following table describes the survival of patients treated from disease X from 2015 to 2017 followed for 3 years (assuming no loss to follow-up).If a person is treated and using all the information from the table,what is the probability of surviving 3 years after treatment?

A) 0.29
B) 0.33
C) 0.61
D) 0.67
E) 0.71

Question 7

What is the effective number exposed to risk of dying in the 13- to 24-month interval? Use the following table to answer the question. Survival of Patients With Metastatic Cancer Z Following Diagnosis
$\begin{array}{|l|l|l|l|l|l|l|l|}\hline \begin{array}{l}\text { Interval } \\\text { since } \\\text { beginning } \\\text { treatment } \\\text { (months) }\end{array} & \begin{array}{l}\text { Alive at } \\\text { beginning } \\\text { of } \\\text { interval }\end{array} & \begin{array}{l}\text { Died } \\\text { during } \\\text { interva } \\1\end{array} & \begin{array}{l}\text { Withdre } \\\text { w during } \\\text { interval }\end{array} & \begin{array}{l}\text { Effective } \\\text { number } \\\text { exposed } \\\text { to risk of } \\\text { dying }\end{array} & \begin{array}{l}\text { Proporti } \\\text { on who } \\\text { died } \\\text { during } \\\text { interval }\end{array} & \begin{array}{l}\text { Proportion } \\\text { who did not } \\\text { die during } \\\text { interval }\end{array} & \begin{array}{l}\text { Cumulative } \\\text { proportion } \\\text { who } \\\text { survived } \\\text { from } \\\text { enrollment } \\\text { to end of } \\\text { interval }\end{array} \\\hline x & I_{x} & d_{x} & W_{x} & I_{x}^{\prime} & q_{x} & p_{x} & P_{x} \\\hline 1-12 & 200 & 10 & 40 & & & & \\\hline 13-24 & 150 & 20 & 30 & & & & \\\hline 25-36 & 100 & 30 & 20 & & & & \\\hline 37-48 & 50 & 40 & 10 & & & & \\\hline\end{array}$

A) 40
B) 90
C) 120
D) 135
E) 160