eAccrual: computes the expected cumulative enrollment (accrual) given a set of piecewise constant enrollment rates and times.

library(tibble)
library(dplyr)
#library(gsDesign2)
devtools::load_all()

Introduction of `eAccrual()`

For the enrollment in the first 3 months, it is exactly \(3 \times 5 = 15\).

eAccrual(x = 3,
         enrollRates = tibble(duration = c(3, 3, 18), rate = c(5, 10, 20)))

## [1] 15

For the enrollment in the first 6 months, it is exactly \(3 \times 5 + 3 \times 10 = 45\).

eAccrual(x = 6, 
         enrollRates = tibble(duration = c(3, 3, 18), rate = c(5, 10, 20)))

## [1] 45

For the enrollment in the first 24 months, it is exactly \(3 \times 5 + 3 \times 10 + 18 * 20 = 405\).

eAccrual(x = 24, 
         enrollRates = tibble(duration = c(3, 3, 18), rate = c(5, 10, 20)))

## [1] 405

For the enrollment after 24 months, it is the same as that from the 24 months, since the enrollment is stopped.

eAccrual(x = 25, 
         enrollRates = tibble(duration = c(3, 3, 18), rate = c(5, 10, 20)))

## [1] 405

Instead of compute the enrolled subjects one time point by one time point, we can also compute it once.

eAccrual(x = c(3, 6, 24, 25), 
         enrollRates = tibble(duration = c(3, 3, 18), rate = c(5, 10, 20)))

## [1]  15  45 405 405

TODO