irtoys (version 0.1.4)

scp: Plot observed and predicted scores against ability

Description

Produces a plot of IRT true scores (test response function at the estimated ability) with a confidence band (plus/minus standard error). The observed sum scores are shown in red.

Usage

scp(resp, ip, theta=NULL)

Arguments

resp

A matrix of binary responses to a test, with persons as rows and items as columns.

ip

Item parameters: a matrix with one row per item, and three columns: [,1] item discrimination $a$, [,2] item difficulty $b$, and [,3] asymptote $c$.

theta

An object containing ability estimates, as output by function mlebme or eap. If NULL, MLE will be estimated from resp and ip.

Value

• None

See Also

mlebme, eap, tsc, trf

Examples

data(Scored)
p.2pl <- est(Scored, model="2PL", engine="ltm")
scp(Scored, p.2pl)