simulation-based power analysis for chi2

chi2_powersim.R

library(tidyverse)
library(purrr)

n1 = 12
n2 = 30
nsims = 10

get_chi2 <- function(x) {
  p1 <- rbinom(1, size = n1, prob = x$p1)
  p2 <- rbinom(1, size = n2, prob = x$p2)
  
  mat <- matrix(c(p1, n1 - p1, p2, n2 - p2), byrow=TRUE, nrow = 2)
  x$pval <- chisq.test(mat)$p.val
  return(x)
}

sims <- expand.grid(p1 = seq(0,1,.1), 
            p2 = seq(0,1,.1), 
            sim = 1:nsims) %>%
  as_tibble %>%
  mutate(index = 1:n()) %>%
  split(.$index) %>%
  map_df(get_chi2)

sims %>%
  group_by(p1, p2) %>%
  summarise(power = mean(pval < .05, na.rm=TRUE))