Expected Events (Two-arm Study)

Program Code

The program is written in R.


George SL and Desu MM. Planning the size and duration of a clinical trial studying the time to some critical event. J Chronic Dis. 1971; 27(1): 15-24.


This program calculates an analysis time for a given proportion of total events, or a proportion of total events for a given analysis time. The calculations are provided both under the assumption of the null hypothesis (equal hazards in the two arms) and under the alternative hypothesis (hazard rate in the experimental arm is different from the standard arm). A table of expected events by month for the entire course of accrual and follow-up can be generated. For a time t with associated accrual period T, the expected events can be calculated by:

$$E[D(t)] = {\gamma t* \over 2} (p_1(t) + p_2(t))$$


Input Items

Note: The specific inputs required will depend upon which calculation is requested.

Output Items

There are three options for calculations. The default option is a table of results by month, under the null and under the alternative hypothesis. The second and third options provide expected events for a given time, or time at which the expected proportion of events have occurred.