size.ci.icc: Sample size for a intraclass correlation confidence interval

In statpsych: Statistical Methods for Psychologists

Sample size for a intraclass correlation confidence interval

Description

Computes the sample size required to estimate an intraclass correlation with desired confidence interval precision. This type of intraclass correlation can be used to describe the reliability of a single measurement (e.g., a single rater or a single form of a test). This intraclass correlation assumes a two-factor (subject x measurement) model. Use the size.ci.cronbach function to determine the sample size required to estimate the reliability of a sum or average of r measurements (e.g., items) with desired confidence interval precision.

Usage

size.ci.icc(alpha, icc, r, w)

Arguments

alpha	alpha value for 1-alpha confidence
icc	intraclass correlation planning value
r	number of measurements (raters, forms, occasions)
w	desired confidence interval width

Details

Specifying an intraclass correlation planning value for a conservatively large sample size requirement is not straightforward with an intraclass correlation. For r = 2, the sample size requirement is largest for an intraclass correlation of zero. But for r = 3, 4, 5, 10, 20, and 40 an intraclass correlation planning value of about .26, .33, .38, .43, .44, and .45, respectively, maximizes the sample size requirement.

Value

Returns the required sample size

References

\insertRef

Bonett2002bstatpsych

Examples

size.ci.icc(.05, .70, 3, .2)

# Should return:
# Sample size
#          68
 

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