DIF effect sizes plot — gg

type = "effect" shows the signed expected-score difference for each item, with flagged items highlighted; type = "curves" overlays the expected item score curves of each group for the chosen (by default the flagged) items.

Usage

gg_dif(
  x,
  type = c("effect", "curves"),
  which.items = NULL,
  theta_lim = c(-4, 4)
)

Arguments

x: an mv_dif object from dif().
type: "effect" or "curves".
which.items: items to draw for type = "curves", by name. Defaults to the flagged items, or the item with the largest effect if none is flagged.
theta_lim: range of the latent trait for type = "curves".

Value

A ggplot object.

Examples

# \donttest{
set.seed(1)
a <- matrix(rlnorm(8, 0.2, 0.3)); d <- matrix(rnorm(8))
d2 <- d; d2[1] <- d2[1] - 1
data <- rbind(simdata(a, d, 400, itemtype = "2PL"),
              simdata(a, d2, 400, itemtype = "2PL"))
res <- dif(data, group = rep(c("F", "M"), each = 400))
gg_dif(res)

gg_dif(res, type = "curves")

# }