Quick power analysis

power-analysis.R

# Power analysis examples to answer quick questions.
# - using pwr package in R
# - see also http://www.statmethods.net/stats/power.html
# --------------------------------------------------

# setup
library(pwr)
p <- 0.05
power <- 0.80

# Summary of possible errors
cat("For given p/power, you have\n  ", p * 100, "% chance to find an effect which is not there (Type 1)\n  ",
  100 * (1 - power), "% chance to miss an effect which is there (Type 2)")
  

# Two-sample t-test
#   How many people for a given effect (in _each_ group)
d <- 0.2
pwr.t.test(d = d, sig.level = p, power = power, type = "two.sample")

# Paired t-test
#   How many people for a given effect
d <- 0.2
pwr.t.test(d = d, sig.level = p, power = power, type = "paired")