help for pcmtest

Global and item specific tests of fit for a Partial Credit Model or a Rating Scale Model

pcmtest, [group(numlist)
new
nfit(#)
power(#)
alpha(#)
approximation
sitest
graphics
filegraph({it:filegraph[, replace])]

Description

pcmtest allows testing the fit between observed data and a
partial credit model or a rating scale model.

The global test of fit (test R1m) can only be computed if the data
contains at least two items. Item specific test of fit (Si tests) can only be
computed if the data contains at least three items.

pcmtest is only performed if item difficulties have been
estimated using pcmodel. pcmtest can be performed whether covariates
have been included in pcmodel or not.

Options

group specifies groups of scores, by defining the upper limit of
each group

new allows changing the computation methodology of the pattern
response probabilities between several tests of fit, rather than using the pattern
response probabilities stored in Stata memory.

nfit specifies the size of a virtual sample with items response
distribution strictly identical to that observed (nfit can deal with
over-power problems when fit tests are performed on large samples).

power specifies the desired power for a R1m test, and estimates the
corresponding size of a virtual sample with items response distribution strictly
identical to that observed.

alpha specifies the type I error used to perform the test of fit
(default: 0.05).

approximation Computation of the pattern response probabilities using
simulation instead of Gauss Hermitte quadratures. Computation should be quicker for
high number of items or responses categories.

sitest performs item specific test of fit (Si tests).

graphics displays several graphs (Distribution of the latent trait
depending on the individual scores, graphic of MAP, graphic of
the groups contributions to the R1m statistic, and graphic of the observed and expected
score distribution).

filegraph indicates the filename and path for saving the graphs
(four graphs are store: filegraph_LT_Sc, filegraph_MAP, filegraph_Contrib
and filegraph_Score_Distrib.)

Outputs

e(globalFitTot): Results of the R1m test performed on the observed sample.

e(itemFitTot): Results of the Si tests performed on the observed sample.

e(globalFitPo): Results of the R1m test corresponding
to the indicated power.

e(itemFitPo): Results of the Si tests corresponding
to the indicated power.

e(globalFitTot): Results of the R1m test corresponding
to the indicated sample size.

e(itemFitTot): Results of the Si tests corresponding
to the indicated sample size.

Author

Jean-François Hamel

Email:
jeanfrancois.hamel@chu-angers.fr

Also see

Online: help for pcmodel, gllamm, simirt
, raschtest.