alpNeeded {agpower} | R Documentation |
Function to compute alpha needed (fixed sample size)
Description
Function to compute two-sided alpha needed to achieve target power given a rate ratio. Useful for computing probability to achieve hurdles.
Usage
alpNeeded(N, bta1, thta, tau, lam0, pow = 0.8, ar = 0.5)
Arguments
N |
Sample size. |
bta1 |
log-transform of rate ratio. |
thta |
Variance of frailty parameter. |
tau |
Expected follow-up time. |
lam0 |
Event rate for control. |
pow |
Target power. |
ar |
Allocation ratio (Number control / Total) |
Details
This function computes the two-sided alpha alp. Function assumes a rate ratio < 1 is favourable to treatment.
Value
The two-sided alpha level.
Examples
# alpha needed to achieve multiple powers given rate ratio (and other input).
alpNeeded(N = 1000, bta1 = log(0.8), thta = 2, tau = 1, lam0 = 1.1, pow = c( .7, .8))
# alpha needed for many inputs
if (require("dplyr") & require("tidyr")) {
assumptions = tibble(RR = 0.8) %>%
crossing(
thta = c(2, 3, 4),
lam0 = 1.1,
pow = c(0.7, 0.8),
N = c(500, 1000),
tau = 1
) %>%
mutate(
alp = alpNeeded(N = N, bta1 = log(RR), thta = thta, tau = tau, lam0 = lam0, pow = pow)
)
assumptions %>% data.frame()
}
[Package agpower version 0.1.2 Index]