roc_sdt: Model-implied ROC curve from a fitted SDT model

In bmm: Easy and Accessible Bayesian Measurement Models Using 'brms'

Model-implied ROC curve from a fitted SDT model

Description

Computes the receiver operating characteristic (ROC) curve implied by the posterior distribution of a signal detection model fit with bmm(). ROC curves require a response criterion, so they are defined for sdt_yn() and sdt_rating() only (not the criterion-free sdt_mafc() and sdt_ranking()).

Usage

roc_sdt(
  fit,
  conditions = NULL,
  n_points = 100,
  probs = c(0.025, 0.975),
  criterion_points = NULL,
  ...
)

Arguments

fit	A bmmfit object returned by bmm() from an SDT model.
conditions	Optional data frame of predictor values at which to evaluate the model. Column names must match predictor variables used in the formula. If NULL (default), unique predictor combinations are derived from the data.
n_points	Integer. Number of equally-spaced points on the smooth model-implied ROC curve (default 100); used for both binary and rating models. The rating data frame itself still holds K+1 points per draw (K-1 threshold points plus the (0,0) and (1,1) endpoints).
probs	Numeric vector of length 2. Lower and upper quantiles for the credible band (default c(0.025, 0.975)).
criterion_points	Optional. Control of the binary multi-criteria behaviour. NULL (default) auto-detects predictors that vary the criterion only (not d/sdratio) and treats their levels as operating points on one curve. Pass a character vector of column names to force that classification, or FALSE to disable it (one separate curve per predictor combination). Ignored for rating models.
...	Additional arguments passed to brms::posterior_linpred(), such as draw_ids to use a subset of the posterior draws. ndraws is refused: each parameter is drawn by its own call, so random subsets would not match across parameters.

Details

For binary models the ROC is traced analytically from the posterior of d (and sdratio for unequal-variance SDT) over a grid of criterion values. When the criterion varies across conditions but d/sdratio do not (e.g. a base-rate manipulation, as in broeder_schuetz_2009_e3), the several criteria are operating points on a single curve: roc_sdt() returns one smooth curve and attaches the model-implied points (one per criterion level) as a points attribute.

For rating models the K-1 confidence thresholds define K-1 empirical ROC points per posterior draw (returned as the data frame). The smooth model-implied curve is traced over a virtual cut from the posterior of d (and sdratio) and attached as the summary attribute, with the K-1 thresholds attached as the points attribute (labelled t1..t(K-1)) so they fall on the curve. For version = "metad" the smooth curve is the type-1 (d, sdratio) ROC and the threshold points are the model's confidence operating points; they lie inside the curve when the M-ratio is below 1, by the amount of the metacognitive inefficiency.

Value

A data frame of class "bmm_sdt_roc" with columns FA, Hit, .draw, and any condition columns. The object carries a summary attribute (FA, Hit_mean, Hit_lower, Hit_upper) with the smooth model-implied curve, and a points attribute with the model-implied operating points: one per criterion level for binary multi-criteria fits, or the K-1 confidence thresholds (labelled t1..t(K-1)) for rating fits. It also carries the attributes probs, model_class, dist, is_rating and conditions, which the print() and plot() methods read. The Hit_lower and Hit_upper columns in the summary attribute are the pointwise posterior quantiles of the hit rate at each criterion value, plotted at that criterion's posterior-mean false-alarm rate; this band does not include uncertainty in the false-alarm rate and is narrower than a credible band at a fixed false-alarm rate.

See Also

auc_sdt(), roc_observed(), plot.bmm_sdt_roc()

Examples

## Not run: 
# Three base-rate conditions shift the criterion, which identifies sdratio
dat <- expand.grid(id = 1:20, stimulus = c(0L, 1L),
                   condition = c("liberal", "neutral", "strict"))
dat$n_trials <- 100L
# simulated as bias, measured from the midpoint between the means (0 = boundary at the midpoint)
criteria <- c(liberal = -0.5, neutral = 0, strict = 0.5)
dat$n_old <- rsdt_yn(nrow(dat), dat$n_trials, dat$stimulus, d = 1.5,
                     bias = criteria[as.character(dat$condition)],
                     sdratio = 1.3)

fit <- bmm(
  formula = bmf(d ~ 1, criterion ~ 0 + condition, sdratio ~ 1),
  data = dat,
  model = sdt_yn(response = "n_old", stimulus = "stimulus",
                 n_trials = "n_trials"),
  cores = 4,
  backend = "cmdstanr"
)

roc <- roc_sdt(fit)
roc
plot(roc, observed = roc_observed(fit))
plot(roc, observed = roc_observed(fit), scale = "quantile")

## End(Not run)

bmm documentation built on Oct. 16, 2026, 9:08 a.m.