Power-Based Approach for the Number of Subjects Required for a Study of Interobserver Agreement with Four Outcome Categories

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Description

This function provides detailed sample size estimation information to determine the number of subjects that are required to test the hypothesis H_0: κ = κ_0 vs. H_1: κ = κ_1, at two-sided significance level α, with power, 1 - β. This version assumes that the outcome is multinomial with four levels.

Usage

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Power4Cats(kappa0, kappa1, props, raters=2, alpha=0.05, power=0.80)

Arguments

kappa0

The null hypothesis for the κ hypothesis test.

kappa1

The alternate hypothesis for the κ hypothesis test.

props

The anticipated prevalence of the desired traits. Note that this four element vector must sum to one.

raters

The number of raters that are available. This function allows between 2 and 6 raters.

alpha

The desired type I error rate.

power

The desired level of power, recall power = 1 - type II error.

Details

This function provides detailed sample size estimation tools for studies of interobserver agreement with four levels. This function employs the power approach, rejecting κ_0 in favour of κ_1 for a pre-specified significance level and power. Note that a warning message is provided if any of the expected cell counts are less than 5.

Value

N

The calculated sample size.

kappa0

The specified null hypothesis.

kappa1

The specified alternative hypothesis.

props

The anticipated proportion of individuals with the outcome.

raters

The number of raters.

alpha

The desired type I error rate.

power

The desired level of power, recall power = 1 - type II error.

Author(s)

Michael Rotondi, mrotondi@uwo.ca

References

Donner A, Rotondi MA. (2010). Sample Size Requirements for Interval Estimation of the Kappa Statistic for Interobserver Agreement Studies with a Binary Outcome and Multiple Raters. International Journal of Biostatistics 6:31.

Altaye M, Donner A, Klar N. (2001). Procedures for Assessing Interobserver Agreement among Multiple Raters. Biometrics 57:584-588.

Donner A. (1999). Sample Size Requirements for Interval Estimation of the Intraclass Kappa Statistic. Communication in Statistics 28:415-429.

Bartfay E, Donner A. (2001). Statistical Inferences for Interobserver Agreement Studies with Nominal Outcome Data. The Statistician 50:135-146.

Donner A, Eliasziw M. (1987) Sample size requirements for reliability studies. Statistics in Medicine 6:441-448.

See Also

CI4Cats

Examples

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## Not run: Suppose an investigator would like to determine the required sample size to test 
kappa0=0.4 vs. kappa1=0.6 with alpha=0.05 and power=0.80 in a study of 
interobserver agreement.  Further suppose that the prevalence of the categories is 
0.30, 0.30, 0.30 and 0.10.
## End(Not run)
Power4Cats(kappa0=0.4, kappa1=0.6, props=c(0.30, 0.30, 0.30, 0.10), alpha=0.05, power=0.80);