Expected Events on a Study

Program Code

The program is written in JavaScript.


Follow-up Time: Enter the number of years between the last patient accrual to the time of the final analysis.

Accrual Time: Enter the number of years of patient accrual.

Sample Size: Enter n, the planned sample size.

Hazard rate: Enter l, the exponential event rate.

Survival probability and time(default): Enter a time, t (in years), and the probability of patients alive at that time, S(t). The program will calculate l as follows.


Percentage of patients cured: A number between 0 and 1.

Calculation of the Expected Number of Events

Probability of event at analysis time is

P(event|Analysis time t)=1 - e(-l*follow)*(1-e(-l*accrual))/l*accrual).

At times before accrual has completed

P(event|t) =(l-1e(-l t) + t - l-1)/accrual.

At other times

P(event|t) = 1 - e(-l (t-accrual))*(1-e(-l*accrual))/(l*accrual).

The survival density f(t) is assumed to be exponential with rate l and cure rate p, i.e.,



There are three options for calculations. The default option is a table of results in new page. The second and third options provide expected events for a given time, or time at which the expected proportion of events have occurred.