Data with responses of naive mock jurors to the conventional
conventional two-option verdict (guilt vs. acquittal) versus a
three-option verdict setup (the third option was the Scottish
'not proven' alternative), in the presence/absence of conflicting
testimonial evidence.
Usage
data("MockJurors")
Format
A data frame containing 104 observations on 3 variables.
verdict
factor indicating whether a two-option or
three-option verdict is requested. (A sum contrast rather
than treatment contrast is employed.)
conflict
factor. Is there conflicting testimonial evidence?
(A sum contrast rather than treatment contrast is employed.)
confidence
jurors degree of confidence in his/her verdict,
scaled to the open unit interval (see below).
Details
The data were collected by Daily (2004) among first-year psychology
students at Australian National University. Smithson and Verkuilen (2006)
employed the data scaling the original confidence (on a scale 0–100)
to the open unit interval: ((original_confidence/100) * 103 - 0.5) / 104.
The original coding of conflict in the data provided from Smithson's
homepage is -1/1 which Smithson and Verkuilen (2006) describe to mean
no/yes. However, all their results (sample statistics, histograms, etc.)
suggest that it actually means yes/no which was employed in MockJurors.
Deady, S. (2004).
The Psychological Third Verdict: 'Not Proven' or 'Not Willing to Make a Decision'?
Unpublished honors thesis, The Australian National University, Canberra.
Smithson, M., and Verkuilen, J. (2006).
A Better Lemon Squeezer? Maximum-Likelihood Regression with
Beta-Distributed Dependent Variables.
Psychological Methods, 11(7), 54–71.
See Also
betareg, ReadingSkills, StressAnxiety
Examples
data("MockJurors", package = "betareg")
library("lmtest")
## Smithson & Verkuilen (2006, Table 1)
## variable dispersion model
## (NOTE: numerical rather than analytical Hessian is used for replication,
## Smithson & Verkuilen erroneously compute one-sided p-values)
mj_vd <- betareg(confidence ~ verdict * conflict | verdict * conflict,
data = MockJurors, hessian = TRUE)
summary(mj_vd)
## model selection for beta regression: null model, fixed dispersion model (p. 61)
mj_null <- betareg(confidence ~ 1 | 1, data = MockJurors)
mj_fd <- betareg(confidence ~ verdict * conflict | 1, data = MockJurors)
lrtest(mj_null, mj_fd)
lrtest(mj_null, mj_vd)
## McFadden's pseudo-R-squared
1 - as.vector(logLik(mj_null)/logLik(mj_vd))
## visualization
if(require("lattice")) {
histogram(~ confidence | conflict + verdict, data = MockJurors,
col = "lightgray", breaks = 0:10/10, type = "density")
}
## see demo("SmithsonVerkuilen2006", package = "betareg") for more details