btaNeeded2: Function to compute log rate ratio needed (fixed sample size)

In agpower: Recurrent Event Analysis Planning for Robust Andersen-Gill Model

Function to compute log rate ratio needed (fixed sample size)

Description

Function to compute log rate ratio needed to achieve target power at one-sided Type I control level alp/2. Useful to compute critical value (set pow = 0.5).

Usage

btaNeeded2(
  N,
  thta,
  L,
  alp = 0.05,
  pow = 0.8,
  ar = 0.5,
  frailty.type = c("unblind", "blind"),
  interval = c(log(0.5), log(1))
)

Arguments

N	Sample size.
thta	Variance of frailty parameter. If frailty.type = "blind", assumes thta derives from pooled model; if frailty.type = "unblind" assumes thta is from correctly specified model. Default "unblind".
L	Number of events
alp	Two-sided alpha-level.
pow	Target power.
ar	Allocation ratio (Number control / Total)
frailty.type	Indicates whether frailty variance is based on blinded information ("blind") or unblinded ("unblind"). Default "unblind".
interval	Initial search interval for bta1.

Details

This function computes the log rate ratio bta1 as the root of the equation pow2(bta1, N, thta_, L, alp, ar) - pow = 0, where thta_ depends on bta1 if using estimates from blinded analyses. If frailty.type = "blind": thta_ = thtap2thta(thta, bta1); otherwise if frailty = "unblind": thta_ = thta. Function assumes a rate ratio < 1 is favourable to treatment.

Value

The log rate ratio.

Examples

# Based on unblinded estimates

# Based on blinded estimates
btaNeeded2(N = 1000, thta = 2, L = 1000, alp = c(0.01, 0.05), pow = c(.5), frailty.type = "bl")
exp(btaNeeded2(N = 1000, thta = 2, L = 1000, alp = c(0.01, 0.05), pow = c(.5), frailty.type = "bl"))

agpower documentation built on June 8, 2025, 2 p.m.