powerForHalfSizes

library(ggplot2)
library(pwr)

#funcs and params-----------------------------
pwrf <- function(ef,pow){
  normal <- pwr.t.test(d = ef, type = "two.sample",
             alternative = "two.sided",
             power = pow)$n
  half <- pwr.t.test(d = (ef/2), type = "two.sample",
             alternative = "two.sided",
             power = pow)$n
  return(half/normal)
}
pwrfANOVA <- function(ef,pow){
  normal <- pwr.anova.test(f = ef, k = 4,
                       power = pow)$n
  half <- pwr.anova.test(f = (ef/2), k = 4,
                     power = pow)$n
  return(half/normal)
}

#t.test---------------------------------------
esTest <- seq(0.001,2,by = 0.001)
df <- data.frame(es = NA, ratio = NA, pow = NA)
for (pw in seq(0.5,0.95, by = 0.05)){
  p <- sapply(esTest, function(x) pwrf(x,pw))
  d <- data.frame(es = esTest,
                  ratio = p,
                  pow = rep(pw, length(p))
                  )
  df <- rbind(df, d)
  
}

df <- df[2:dim(df)[1],]
df$pow <- factor(df$pow)


ggplot(df, aes(x = es, y = ratio, color = pow)) + geom_line() +
  theme_minimal() + xlab("Effect Size") + ylab("Sample Ration when es/2") +
  ggtitle("Sample Size Ratio for Two Sample T-Test when es is halved")

#ANOVA---------------------------------------
esTest <- seq(0.001,1,by = 0.001)
df <- data.frame(es = NA, ratio = NA, pow = NA)
for (pw in seq(0.5,0.95, by = 0.05)){
  p <- sapply(esTest, function(x) pwrfANOVA(x,pw))
  d <- data.frame(es = esTest,
                  ratio = p,
                  pow = rep(pw, length(p))
  )
  df <- rbind(df, d)
  
}

df <- df[2:dim(df)[1],]
df$pow <- factor(df$pow)


ggplot(df, aes(x = es, y = ratio, color = pow)) + geom_line() +
  theme_minimal() + xlab("Effect Size") + ylab("Sample Ration when es/2") +
  ggtitle("Sample Size Ratio for ANOVA when es is halved")