mdd.fisher.exact {MDD}R Documentation

MDD for Fisher's Exact Test

Description

Calculate the minimum detectable difference for a two-sample Fisher's exact test. Also computes the true treatment response rates closest to the control response rate that would be detected with a given power.

Usage

mdd.fisher.exact(placebo.size, treat.size, prob.placebo, alpha = 0.05, pow = 0.8, 
                 alternative = "two.sided")

Arguments

placebo.size number of subjects in control group.
treat.size number of subjects in treatment group.
prob.placebo anticipated proportion of responses in control group.
alpha significance level.
pow power.
alternative indicates the alternative hypothesis and must be one of "two.sided", "greater", or "less". You can specify just the initial letter.

Details

alternative = "less" is the alternative that has the treatment group mean less than the control group mean.

Value

A list with the following components:

actual true treatment reponse rate(s) that would be detected as significant, with power pow, at significance level alpha.
observed matrix with the number and proportion of observed treatment responses that would be significant, conditional on the number and proportion of observed control responses.

Author(s)

Don Barkauskas (barkda@wald.ucdavis.edu)

References

See fisher.test for references.

See Also

chisq.test for an asymptotic test

gui.mdd for a GUI version

Examples

fish.ex <- mdd.fisher.exact(20,40,.25)

#For a two-sided test at significance level 0.05 and power 80%, with 20 control 
#subjects and 40 treatment subjects and an assumed control response rate of 25%.

fish.ex$actual

#If the true treatment response rate is less than 0.01811086 or greater than
#0.65370397, it will be detected with 80% power.

fish.ex$observed

#For example, if there are 6 observed control repsonses (observed response rate 
#of 30%), then either 3 or fewer or 25 or more treatment responses (7.5% and 
#62.5% response rates, respectively) will be declared significant.
#
#Compare to mdd.chisq(20,40,.25).

rm(fish.ex)

[Package MDD version 0.5 Index]