A function to calculate the N individuals/groups required to estimate the ICC with a desired confidence interval

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Description

Given a predicted ICC and k measures per individual/group, this function will calculate the N individuals/groups required to obtain a desired confidence interval w(according to Bonett, 2002).

Usage

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Nest(est.type = c("hypothetical", "pilot"), w, ICC = NULL, k = NULL,
x = NULL, y = NULL, data = NULL, alpha = 0.05)

Arguments

est.type

character string of either "hypothetical" indicating usage of the given values of k and ICC or if "pilot" is specified then to calculate these from the dataset provided. Also, just the first letter may be used

w

desired width of the confidence interval about the ICC estimate

ICC

expected intraclass correlation coefficient

k

number of measurements per individual or group

x

column name of data indicating the individual or group ID from a pilot study

y

column name of data indicating the measurements from a pilot study

data

a data.frame from a pilot experiment

alpha

the alpha level to use when estimating the confidence interval

Details

More than one ICC or k may be given. In this case, the return value is a dataframe with rows representing the values of the specified ICCs and the columns yield the different k values.

Value

data.frame indicating the N number of individuals or groups to use to estimate the given ICC with a desired confidence interval width. Rows represent different levels of ICC while columns indicate different levels of k measurements per individual/group.

Author(s)

Matthew Wolak matthewwolak@gmail.com

References

D.G. Bonett. 2002. Statistics in Medicine, 21(9): 1331-1335.

M.E. Wolak, D.J. Fairbairn, Y.R. Paulsen. 2011. Methods in Ecology and Evolution.

See Also

ICCest

Examples

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#Example 1
n1<-Nest("h", w=0.14, ICC=0.1, k=10)
n1

#Example 2
data(ChickWeight)
Nest("p", w=0.14, x=Chick, y=weight, data=ChickWeight)
ex2<-ICCest(Chick, weight, ChickWeight)
ex2$UpperCI-ex2$LowerCI #confidence interval width of pilot study
ex2

#Example 3
Nest("h", w=0.14, ICC=seq(0.05, 0.15, 0.05), k=seq(10,12,1))