Classical test theory and item response theory are two statistical theories for analyzing test performance and relating it to examinee abilities. Classical test theory defines test scores, true scores, and error scores at the test level, assumes weak assumptions about test data, and specifies a linear relationship between ability and item performance. Item response theory defines item characteristic functions at the item level, assumes stronger assumptions about test data, and specifies a nonlinear relationship between ability and item performance.

1. Comparison between Classical Test Theory & Item Response Theory
SAIRA KAZIM (M.Phil Education)
sairakazim@gmail.com
Dimension Classical Test Theory Item Response Theory
Definition Classical test theory is a theory
about test scores that introduces
three concepts-test score (often
called the observed score), true
score, and error score.
Item response theory is a general
statistical theory about examinee item and
test performance and how performance
relates to the abilities that are measured
by the items in the test.
Model Linear Non Linear
Level Test Item
Assumption Weak (i.e., easy to meet test
data)
Strong (i.e., more difficult to meet test
data)
Item Ability
Relationship
Non Specified Item Characteristic Functions
Test Parallel Test Non Parallel Test
Invariance Sample dependent. Sample independent,
Error Equal chance for every one Not equal chance for every one
Sample Size
(for item
parameter
estimation)
200 to 500 (in general) Depends on the IRT model, but the larger
population. i.e., over 500 in general are
needed.
Performance Predictable Non Predictable