FTres function

Freeman-Tukey Residuals

Calculates the Freeman-Tukey residuals for log-linear models of frequency data. If the frequencies are assumed to be Poisson distributed, then the Freeman-Tukey residuals are approximately normal distributed.

FTres(obs, fit)

Arguments

• obs: A numeric vector containing the observed frequencies.
• fit: A numeric vector containing the estimated frequencies.

Details

For an observed frequency $ni$ and the estimated frequency $mi$, the Freeman-Tukey residual $FTi$ is defined as

$FTi = \sqrt(ni)+\sqrt(ni+1)-\sqrt(4mi+1).$

Returns

A numeric vector containing the Freeman-Tukey residuals.

References

Andersson, B., Branberg, K., and Wiberg, M. (2013). Performing the Kernel Method of Test Equating with the Package kequate . Journal of Statistical Software, 55(6) , 1--25. doi:10.18637/jss.v055.i06

Holland, P.W, Thayer, D. (1998). Univariate and Bivariate Loglinear Models for Discrete Test Score Distributions ETS Technical Report No 98-1 .

Author(s)

bjorn.andersson@statistik.uu.se

kenny.branberg@stat.umu.se

marie.wiberg@stat.umu.se

See Also

glm

Examples

#Example data:
P<-c(5, 20, 35, 25, 15)
x<-0:4
glmx<-glm(P~I(x)+I(x^2), family="poisson", x=TRUE)
res<-FTres(glmx$y, glmx$fitted.values)