For every keyed item and response option: the count and proportion
choosing it, the mean location of those persons, and the point-biserial
correlation between choosing the option and the person measure. Locations
and correlations use the rest measure (the person estimate from the other
items), so the analysed item cannot credit its own takers. The keyed
option should attract the ablest persons and carry the only positive
point-biserial; a distractor whose takers are abler than the keyed
option's (with at least min_n takers) is flagged as a possible
miskey.
Arguments
- fit
A fitted object from
raschrun with akey.- items
Optional subset of item names; defaults to every keyed item.
- min_n
Minimum takers for an option to be eligible for the miskey flag.
Value
A data frame with one row per item-option: item,
option, its assigned score, keyed (full credit),
n, prop, mean_location, point_biserial,
and flag.
Examples
set.seed(1); Np <- 400
th <- rnorm(Np)
raw <- sapply(seq(-1, 1, length.out = 6), function(d) {
ok <- rbinom(Np, 1, plogis(th - d))
ifelse(ok == 1, "A", sample(c("B", "C", "D"), Np, replace = TRUE))
})
colnames(raw) <- paste0("M", 1:6)
fit <- rasch(raw, key = setNames(rep("A", 6), colnames(raw)))
head(distractor_analysis(fit))
#> item option score keyed n prop mean_location point_biserial flag
#> 1 M1 A 1 TRUE 277 0.6925 0.2457337 0.23025114 FALSE
#> 2 M1 B 0 FALSE 40 0.1000 -0.3836142 -0.12294026 FALSE
#> 3 M1 C 0 FALSE 38 0.0950 -0.2619386 -0.08678212 FALSE
#> 4 M1 D 0 FALSE 45 0.1125 -0.4096550 -0.13900664 FALSE
#> 5 M2 A 1 TRUE 245 0.6125 0.3067212 0.26204987 FALSE
#> 6 M2 B 0 FALSE 60 0.1500 -0.3834449 -0.15309278 FALSE