Sample size for an intraclass correlation confidence interval using a planning value from a prior study

Computes the sample size required to estimate an intraclass correlation with desired confidence interval precision in applications where an estimated intraclass correlation from a prior study is available. The actual confidence interval width in the planned study will depend on the value of the estimated intraclas correlation in the planned study. An estimated intraclass correlation from a prior study can be used to compute a lower prediction limit for the estimated intraclass correlation in the planned study, which is then used as a planning value in the sample size analysis. The probability that the prediction interval will have a width that is less than the desired width in the planned study is approximately 1 - alpha2.

This sample size approach assumes that the population intraclass correlation that was estimated in the prior study is very similar to the population intraclass correlation that will be estimated in the planned study. If an estimated intraclas correlation from a prior study is not available, the researcher must use expert opinion to guess the value of the intraclass correlation that will be observed in the planned study. The size.ci.icc function uses an intraclass correlation planning value that is based on expert opinion regarding the likely value of the intraclass correlation estimate that will be observed in the planned study.

Usage

size.ci.icc.prior(alpha1, alpha2, cor0, n0, r, w)

Arguments

alpha1

alpha level for 1-alpha1 confidence in the planned study

alpha2

alpha level for the 1-alpha2 prediction interval

cor0

estimated correlation in prior study

n0

sample size in prior study

r

number of measurements (raters, forms)

w

desired confidence interval width

Value

Returns the required sample size

Examples

size.ci.icc.prior(.05, .10, .674, 50, 3, .2)
#>  Sample size
#>          114

# Should return:
# Sample size
#         114