functions-under-development/ci_mean_t.R

In GegznaV/BioStat: Routines for Basic (Bio)Statistics

#' t-distribution based confidence interval of mean
#'
#' Student's t-distribution based confidence interval of mean
#'
#' @inheritParams ci_mean_boot
#'
#' @return An object (data frame or matrix) with a point estimate and confidence interval of mean.
#' @export
#'
#' @examples
#' set.seed(999555)
#' x <- rnorm(35, 10, 5)
#' ci_mean_t(x)
#
ci_mean_t <- function(x,
                      conf_level = 0.95,
                      na.rm = TRUE,
                      return_df = TRUE) {
    checkmate::assert_numeric(x, all.missing = FALSE)
    checkmate::assert_number(conf_level, lower = 0, upper = 1)

    if (na.rm) {
        x <- x[!is.na(x)]
    }

    n <- length(x)
    SD <- sd(x)
    mean_bar <- mean(x)

    t <- qt((1 - conf_level) / 2, df = (n - 1), lower.tail = FALSE)

    Err  <- t * SD/sqrt(n)

    res <- matrix(c(mean_bar, mean_bar - Err, mean_bar + Err, conf_level),
                  nrow = 1,
                  byrow = TRUE,
                  dimnames = list(NULL,
                                  c("mean", "lower", "upper", "conf_level")))

    if (return_df == TRUE)
        res <- as.data.frame(res)

    res
}