ci.sd: Confidence interval for a standard deviation

In statpsych: Statistical Methods for Psychologists

Confidence interval for a standard deviation

Description

Computes the traditional confidence interval for a population standard deviation using a sample estimate of the standard deviation. The traditional confidence interval assumes normality and is hypersensitive to minor violations of this assumption. This function should be used only if the data appear to come from an approximate normal or mildly platykurtic distribution.

Usage

ci.sd(alpha, sd, n)

Arguments

alpha	alpha value for 1-alpha confidence
sd	estimated standard deviation
n	sample size

Value

Returns a 1-row matrix. The columns are:

• Estimate - estimated standard deviation (from input)

• LL - lower limit of the confidence interval

• UL - upper limit of the confidence interval

Examples

ci.sd(.05, 4.65, 50)

# Should return:
#  Estimate       LL       UL
#      4.65 3.884303  5.79452
 

statpsych documentation built on Jan. 13, 2026, 1:07 a.m.