R/ci.omega2.R

In MBESS: The MBESS R Package

ci.omega2 <- function(F.value=NULL, df.1=NULL, df.2=NULL, N=NULL, conf.level=.95, alpha.lower=NULL, alpha.upper=NULL, ...)
{
#######################################################################
# Thanks to Jason Finley and Antoinette Kroes for helpful comments and for encouraging this function to be included in MBESS.
    
# Preliminary information and function set-up.
if(is.null(alpha.lower) & is.null(alpha.upper))
{
alpha.lower <- (1-conf.level)/2
alpha.upper <- (1-conf.level)/2
}

if ( !is.null(alpha.lower)  &&  !is.null(alpha.upper) ) 
{
conf.level<- 1- alpha.upper - alpha.lower
}

if (alpha.lower>.5 || alpha.lower<0) stop ("'alpha.lower' must be smaller than .5 and nonnegative.")
if (conf.level>1 || conf.level<0) stop ("'conf.level' must be larger than 0 and smaller than 1.")
if (F.value<=0) stop ("'F.value' must be larger than 0.")
# A helpful check, but not a fail-safe 'there is an error' issue.
if (N<=0 || N<=df.1+df.2) stop ("N must be larger than df.1+df.2")

if(!is.null(alpha.lower) & is.null(alpha.upper)) stop("This is a problem with the desired confidence level ('alpha.lower' specified but not 'alpha.upper').")
if(is.null(alpha.lower) & !is.null(alpha.upper)) stop("This is a problem with the desired confidence level ('alpha.upper' specified but not 'alpha.lower').")

if(is.null(df.1) | is.null(df.2) | is.null(N)) stop("You need to specify 'df.1', 'df.2', and 'N'.")
if(is.null(F.value)) stop("You must specify the observed F-value ('F.value') from the analysis of variance.")
##########################################################################

limits <- conf.limits.ncf(F.value = F.value, conf.level = NULL, df.1 = df.1, 
df.2 = df.2, alpha.lower = alpha.lower, alpha.upper = alpha.upper)

# CI from Steiger (2004) Eq. 16. This is the CI for Omega^2. 
lower_limit <- limits$Lower.Limit/(limits$Lower.Limit + N)
upper_limit <- limits$Upper.Limit/(limits$Upper.Limit + N)

return(list(lower_limit_omega2=lower_limit, upper_limit_omega2=upper_limit))
}