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IRT2, CRT, TEST
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Classical Test Theory
Generalizability Theory
Item Response Theory
=
Variance discriminate, but variance due to what (facets)?
Decompose variance into e.g. person, p
and item, i. Identify facets causing desired,undesired variation
•Probabilistic rather than deterministic•Item (question) level discrimination, not just test level
•Account for person ability and item difficulty in same scale
A person should have greater probability of
success on easier item than more difficult
item.
A more able person should have greater
probability of success on assessment items
than a less able person.
Rasch analysis (in a nutshell)-how good is
your test item fitting to these assertions?
Bar height = 1.80m
(item difficulty)
Personal best = 2.10m(Person ability)
Personal best = 1.72m(Person ability)
Personal best = 1.50(Person ability)
Personal best = 1.80m
(Person ability)What’s the probability he will clear the bar?50:50?Anxiety? Preparation?
Etc.
Wright map
ICC and IIC
Polytomous IRT (e.g. partial credit model)
Fit statistics to Rasch model (chi-square)
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Pro
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Ability
Item 1 Item 2 Item 3
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0.5
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1.5
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In
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Ability
Item 1 Item 2 Item 3 Total