Dependency of Anxiety on Stress
Stress and anxiety among nonclinical women in Townsville, Queensland, Australia.
data("StressAnxiety")A data frame containing 166 observations on 2 variables.
score, linearly transformed to the open unit interval (see below).
score, linearly transformed to the open unit interval (see below).
Both variables were assess on the Depression Anxiety Stress Scales, ranging from 0 to 42. Smithson and Verkuilen (2006) transformed these to the open unit interval (without providing details about this transformation).
Example 2 from Smithson and Verkuilen (2006) supplements.
Smithson, M., and Verkuilen, J. (2006). A Better Lemon Squeezer? Maximum-Likelihood Regression with Beta-Distributed Dependent Variables. Psychological Methods, 11(7), 54–71.
data("StressAnxiety", package = "betareg")
StressAnxiety <- StressAnxiety[order(StressAnxiety$stress),]
## Smithson & Verkuilen (2006, Table 4)
sa_null <- betareg(anxiety ~ 1 | 1,
data = StressAnxiety, hessian = TRUE)
sa_stress <- betareg(anxiety ~ stress | stress,
data = StressAnxiety, hessian = TRUE)
summary(sa_null)
summary(sa_stress)
AIC(sa_null, sa_stress)
1 - as.vector(logLik(sa_null)/logLik(sa_stress))
## visualization
attach(StressAnxiety)
plot(jitter(anxiety) ~ jitter(stress),
xlab = "Stress", ylab = "Anxiety",
xlim = c(0, 1), ylim = c(0, 1))
lines(lowess(anxiety ~ stress))
lines(fitted(sa_stress) ~ stress, lty = 2)
lines(fitted(lm(anxiety ~ stress)) ~ stress, lty = 3)
legend("topleft", c("lowess", "betareg", "lm"), lty = 1:3, bty = "n")
detach(StressAnxiety)
## see demo("SmithsonVerkuilen2006", package = "betareg") for more detailsPlease choose more modern alternatives, such as Google Chrome or Mozilla Firefox.