freqbump {equate}R Documentation

Frequency Adjustment

Description

This function smooths a frequency distribution by adding a small relative frequency to each score while adjusting the probabilities to sum to one (see Kolen & Brennan, 2004, p. 48).

Usage

freqbump(x, jmin = 10^-6, Kx = length(x))

Arguments

x vector of either counts (summing to the number of examinees) or probabilities (summing to 1). If x does not sum to one it is assumed to be a vector of counts and it is converted to probabilities
jmin the frequency to be added to each score point (default is 10^-6)
Kx integer indicating the number of items in the scale (default is length(x))

Value

Returns a vector of adjusted relative frequencies, as probabilities

Author(s)

Anthony Albano tony.d.albano@gmail.com

References

Kolen, M. J., & Brennan, R. L. (2004) Test Equating, Scaling, and Linking. (2nd ed.), New York: Springer.

See Also

freqtab, freqavg

Examples

set.seed(2005)
x <- round(rnorm(1000,100,10))
xscale <- 70:130
xtab <- freqtab(x,xscale)

# compare freqbump to freqavg:
xbump <- freqbump(xtab[,2])
xavg <- freqavg(xtab)
cbind(xtab,bump=round(xbump*sum(xtab[,2]),6),avg=xavg)

[Package equate version 0.1-1 Index]