Summary

Ceiling and floor effects are common in data. Ceiling or floor effects occur when the tests or scales are relatively easy or difficult such that substantial proportions of individuals obtain either maximum or minimum scores and that the true extent of their abilities cannot be determined.

Ceiling and floor effects, subsequently, causes problems in data analysis. For example, ceiling or floor effects alone would induce, respectively, attenuation or inflation in mean. And both ceiling and floor effects would result in attenuation in variance. This imposes challenges in mean and variance based data analytic methods.

The current version of this package implements methods to deal with challenges associated with ceiling/floor effects in the data using paramtric methods that assume normality for the true scores.

Helper functions

The package contains a helper function threeganova.sim that would generate a three-group anova data with a standard normal control group and positive/negative treatment groups of effect with same magnitudes. In addition, one can specify the standard deviation in positive treatment group. To see the specifics of the function, user can enter ?threeganova.sim in the R console.

Another helper function included in the package is induce.cfe where the user can manually induce ceiling and floor effects to healthy data. To see the specifics of the function, user can enter ?induce.cfe in the R console.

Moreover, the function F.star.test allows user to conduct a Brown-Forsythe F star test. This is a variant of the commonly used F test. F star test is robust agaisnt violations of homogeneity of variance (HOV) assumption for the F test.

Functions for data analyses

The current version of the package includes three functions that can facilitate the user to conduct data analyses for data with ceiling/floor effects.rec.mean.var estimates the true mean and variance of the data with ceiling/floor effects. That is, as mentioned in the summary, the observed mean and variance of data with ceiling/floor effects are often biased. Thus, rec.mean.var aims to help the user to recover the mean and variance of the data were ceiling/floor effects absent. lw.t.test conducts a t test that adjusts for ceiling/floor effects in the data. As lw.t.test also uses Welch's t test, the adjusted t test is robust against HOV violation. lw.f.star conducts a F star test for one-way ANOVA that adjusts for ceiling/floor effects in the data. lw.f.star is also robust against HOV violation.

example

library(DACF)
# Simulate healthy data for two groups
x.1=rnorm(300,2,4)
x.2=rnorm(300,3,5)
# check mean and variance for simulated healthy data
mean(x.1);var(x.1)
mean(x.2);var(x.2)
# induce ceiling effects of 20% in group 1
x.1.cf=induce.cfe(.2,0,x.1)
# induce floor effects of 10% in group 2
x.2.cf=induce.cfe(0,.1,x.2)
# recover the mean and variance for ceiling/floor data
rec.mean.var(x.1.cf)
rec.mean.var(x.2.cf)
# conduct a t test on healthy data
t.test(x.1,x.2)
t.test(x.1.cf,x.2.cf)
# conduct an adjusted t test on ceiling/floor data
lw.t.test(x.1.cf,x.2.cf,"a")
lw.t.test(x.1.cf,x.2.cf,"b")
# generate a dataframe for ANOVA demo
testdat=threeganova.sim(10000,.0625,1)
# induce ceiling/floor effects in the data
testdat.cf=testdat
testdat.cf[testdat.cf$group==2,]$y=induce.cfe(.2,0,testdat.cf[testdat.cf$group==2,]$y)
# conduct an adjusted F star test on ceiling/floor data
lw.f.star(testdat.cf,y~group,"a")
lw.f.star(testdat.cf,y~group,"b")


QMmmmLiu/DACFD documentation built on Nov. 18, 2017, 8:53 a.m.