Confidence Interval Funciton

[spsanderson]

confidence_interval <- function(vector, interval) {
  # Standard deviation of sample
  vec_sd <- sd(vector)
  # Sample size
  n <- length(vector)
  # Mean of sample
  vec_mean <- mean(vector)
  # Error according to t distribution
  error <- qt((interval + 1)/2, df = n - 1) * vec_sd / sqrt(n)
  # Confidence interval as a vector
  result <- c("lower" = vec_mean - error, "upper" = vec_mean + error)
  return(result)
}

> confidence_interval(rnorm(100), .025)
      lower       upper 
-0.02767951 -0.02181560 
> confidence_interval(rnorm(100), 1 - 0.025)
     lower      upper 
-0.3523130  0.1597769