*! version 1.0 2022.02.11
help uirt_inf

Title

uirt_inf -- Postestimation command of uirt to plot information functions

Syntax

uirt_inf [varlist] [,options]

varlist must include only variables that were declared in the main list of items of current uirt run.
If varlist is skipped or asterisk * is used and no options are added, uirt_inf will create a graph with item information functions
for all items declared in main list of items of current uirt run.

Options

test test-level I(theta)

se conditional standard error, instead of I(theta); only with test

groups group-specific I(theta); only with test and a multi-group model

tw(twoway_options) twoway graph options to override default graph layout

Description

uirt_inf is a postestimation command of uirt.
It allows to plot the information functions of individual items
or the information function of a test consisting of items provided in varlist.
Test information function is obtained with test option. It is equal to the sum of individual item information functions
and a term that accounts for the prior distribution of theta (reciprocal of the variance of the prior).
In a multi-group model, this may result in different shapes of test information functions for each group.
By default uirt_inf will plot the test information function only for the reference group.
If you wish to see the group-specific I(theta) plots, you should add the groups option.
When test is used together with se, a function of standard error of the estimate of theta is plotted instead of the default I(theta).
It is equal to the reciprocal of the square root of test information function.
Group-specific standard error plots in multi-group models can be obtained by adding the groups option.

Options

test creates a graph with test information function for items specified in varlist.
It can be modified with se to produce standard error plot.
In multi-group models, it can be also modified with groups to produce group-specific plots.

se modifies the test option, to produce a plot with standard error of theta estimates.
In multi-group models, it can be also modified with groups to include group-specific plots.

groups modifies the test-level graphs to include group-specific plots.
It will take no effect in a single-group model, or if option test is not included.

tw(twoway_options) it is used to add user-defined twoway graph options to override the default graph layout,
like: xtitle() or scheme() etc.

Examples

Setup

. webuse masc2

Fit a two-group IRT model with uirt

. uirt q*,gr(female)

Item information function for q1

. uirt_inf q1

Item information functions for all items

. uirt_inf

Test information function assuming all items

. uirt_inf *, test

Group-specific test information functions

. uirt_inf *, test gr

Create a graph with group-specific standard error functions, name it for use in next step

. uirt_inf *, test se gr tw(name(se_theta_inf))

Add the EAP estimate and its standard error to the dataset with uirt_theta;
create a scatterplot of SE(EAP) and EAP; combine with the graph from previous step to compare the results

. uirt_theta ,eap

. tw (scatter se_theta theta if female==0,yvarlab(female=0) ) || (scatter se_theta theta if female==1,yvarlab(female=1)), xscale(range(-4 4)) name(se_theta_eap) ytitle(Standard error of EAP) xtitle(EAP of theta) title (EAP - error vs estimates)

. gr combine se_theta_eap se_theta_inf, ycommon

Stored results

uirt_inf does not store anything in r():

Author

Bartosz Kondratek
everythingthatcounts@gmail.com