pi.var: Prediction limits for a sample variance in a future study

In statpsych: Statistical Methods for Psychologists

Prediction limits for a sample variance in a future study

Description

Computes a two-sided or one-sided prediction limit for the estimated variance in a future study for a planned sample size of n. The prediction limit uses a variance estimate from a prior study of size n0.

Several confidence interval sample size functions in this package require a planning value of the expected sample variance in the planned study. A one-sided upper variance prediction limit is useful as a variance planning value for a conservatively large sample size required to obtain a confidence interval with desired width. This strategy for specifying a variance planning value is useful in applications where the population variance in the prior study is assumed to be very similar to the population variance in the planned study.

For more details, see Section 1.31 of Bonett (2021, Volume 1)

Usage

pi.var(alpha, var, n0, n, type)

Arguments

alpha	alpha value for upper 1-alpha confidence
var	estimated variance from prior study
n0	sample size used to estimate the variance
n	planned sample size of future study
type	set to 1 for two-sided prediction interval set to 2 for one-sided upper prediction limit set to 3 for one-sided lower prediction limit

Value

Returns two-sided or one-sided prediction limit(s) of an estimate variance in a future study

References

\insertRef

Hahn1972statpsych

\insertRef

Bonett2021statpsych

Examples

pi.var(.05, 15, 40, 100, 2)

# Should return:
#      UL
# 23.9724
 

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