mirt (version 1.46.1)

LSAT7: Description of LSAT7 data

Description

Data from Bock & Lieberman (1970); contains 5 dichotomously scored items obtained from the Law School Admissions Test, section 7.

Data from

Author

Phil Chalmers

References

Bock, R. D., & Lieberman, M. (1970). Fitting a response model for n dichotomously scored items. Psychometrika, 35(2), 179-197.

Bock, R. D., & Lieberman, M. (1970). Fitting a response model for n dichotomously scored items. Psychometrika, 35(2), 179-197.

Examples

# \donttest{
dat <- expand.table(LSAT7)
head(dat)
itemstats(dat)

# fit 2PL model for each item
(mod <- mirt(dat))
coef(mod)

# monotonic splines models (see Winsberg, Thissen, and Wainer, 1984)
mod_monospline <- mirt(dat, itemtype = 'monospline')
anova(mod, mod_monospline)
plot(mod_monospline)

# compare item 1 trace-lines
i1 <- extract.item(mod, 1)
i1mono <- extract.item(mod_monospline, 1)
theta <- matrix(seq(-6, 6, length.out=100))
twoPL <- probtrace(i1, theta)[,2]
monospline <- probtrace(i1mono, theta)[,2]

plot(twoPL ~ theta, type = 'l')
lines(monospline ~ theta, col='red')

# }

# \donttest{
dat <- expand.table(LSAT7)
head(dat)
itemstats(dat)

(mod <- mirt(dat, 1))
coef(mod)
# }