Consider the data table showing patients in a trial in which 30 are given a placebo and 20 are given an experimental drug and the deaths are recorded over a period of 24 months.

$\begin{array}{c}
\underline { \text { Control} } \quad \quad \quad \quad \quad \quad \quad \quad\underline { \text { Exp. drug}}\
\begin{array}{cccc}
\text { Time } & \text { \# at risk } & \text { Deaths } & \text { \# at risk } & \text { Deaths } \
3 & 30 & 5 & 20 & 1 \
6 & 25 & 6 & 18 & 2 \
9 & 19 & 3 & 16 & 1 \
12 & 16 & 3 & 15 & 2 \
24 & 13 & 2 & 13 & 1
\end{array}\end{array}$
-What proportion of patients died during the interval between 6 and 9 months after starting the trial?

Question

Consider the data table showing patients in a trial in which 30 are given a placebo and 20 are given an experimental drug and the deaths are recorded over a period of 24 months.
​
 $\begin{array}{c}
\underline {  \text {  Control}   }  \quad \quad \quad \quad \quad \quad \quad \quad\underline { \text { Exp. drug}}\
\begin{array}{cccc}
\text { Time } & \text { \# at risk } & \text { Deaths } & \text { \# at risk } & \text { Deaths } \
3 & 30 & 5 & 20 & 1 \
6 & 25 & 6 & 18 & 2 \
9 & 19 & 3 & 16 & 1 \
12 & 16 & 3 & 15 & 2 \
24 & 13 & 2 & 13 & 1
\end{array}\end{array}$
-What proportion of patients died during the interval between 6 and 9 months after starting the trial?

Quizplus · Accepted Answer

The proportion of patients who died during the interval between 6 and 9 months after starting the trial is the number of deaths during that interval divided by the number of patients at risk at the beginning of the interval. In the control group, there were 6 deaths during that interval and 25 patients at risk at the beginning of the interval, so the proportion of patients who died during that interval is 6/25 = 0.24. In the experimental drug group, there were 3 deaths during that interval and 18 patients at risk at the beginning of the interval, so the proportion of patients who died during that interval is 3/18 = 0.167. The overall proportion of patients who died during that interval is the weighted average of these two proportions, with weights equal to the number of patients in each group. So the overall proportion of patients who died during that interval is (0.24 * 30 + 0.167 * 20) / (30 + 20) = 0.114.

Consider the Data Table Showing Patients in a Trial in Which