Dimensionality
1. How many dimensions?
Unidimensional: when the items of a test reflect only one
attribute (psy dimension)
o E.g. geometry test score > reflects knowledge of
student only if the test items truly represent only the
knowledge of geometry.
o Conceptual homogeneity: when all the test item
responses are functions of same attribute
o Validity and reliability of unidimensional tests are
evaluated for the total score produced by the
test.
Multidimensional test: when items of the test reflect more
than one psychological attributes.
o Leads to Q2
2. If there is more than one dimension are they correlated
with each other or not? (implications for total scores)
Correlated dimensions
o E.g. Stanford-Binet test > has groups of questions
(subsets) that correspond to a different facet of
intelligence (attribute)
, o Each subset is unidimensional and the items have
conceptual homogeneity
o The subset scores are combined > total test score
General attribute= high-order factor
o Each subset is evaluated base on its psychometric
quality > each subset is examined, also the total score
produced by subsets is evaluated.
Uncorrelated dimensions: when dimensions are not or are
weakly assoc.
o Subsets > reflect attributes that are independent and
do not form a high-order factor.
o No total score is computed
1. How many dimensions?
Unidimensional: when the items of a test reflect only one
attribute (psy dimension)
o E.g. geometry test score > reflects knowledge of
student only if the test items truly represent only the
knowledge of geometry.
o Conceptual homogeneity: when all the test item
responses are functions of same attribute
o Validity and reliability of unidimensional tests are
evaluated for the total score produced by the
test.
Multidimensional test: when items of the test reflect more
than one psychological attributes.
o Leads to Q2
2. If there is more than one dimension are they correlated
with each other or not? (implications for total scores)
Correlated dimensions
o E.g. Stanford-Binet test > has groups of questions
(subsets) that correspond to a different facet of
intelligence (attribute)
, o Each subset is unidimensional and the items have
conceptual homogeneity
o The subset scores are combined > total test score
General attribute= high-order factor
o Each subset is evaluated base on its psychometric
quality > each subset is examined, also the total score
produced by subsets is evaluated.
Uncorrelated dimensions: when dimensions are not or are
weakly assoc.
o Subsets > reflect attributes that are independent and
do not form a high-order factor.
o No total score is computed
