#' Control Chart Constant A2
#'
#' Calculate A2 control chart constant from Wheeler's SPC books.
#'
#' @param sample.size A scalar or vector of sample sizes
#' @param n.sigma How many standard errors to use (default 3 for most control charts)
#'
#' @return A scalar or vector with computed constants.
# .spc.cached.constant.A2 <- data.frame(
# sample.size = 2:15,
# A2 = c(1.880, 1.023, 0.729, 0.577,
# 0.483, 0.419, 0.373, 0.337,
# 0.308, 0.285, 0.266, 0.249,
# 0.235, 0.223)
# )
spc.constant.calculation.A2 <- function(
sample.size,
n.sigma = 3
) {
# ret <- NA
#
# idx <- which(.spc.cached.constant.A2$sample.size == sample.size)
# if (length(idx) != 0) {
# ret <- .spc.cached.constant.A2$A2[idx]
# }
#
# ret
sapply(sample.size, FUN = function(i) {
n.sigma/(spc.constant.calculation.d2(i) * sqrt(i))
})
}
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