Dictionary Definition
equating n : the act of regarding as equal [syn:
equation]
User Contributed Dictionary
English
Verb
equating- present participle of equate
Extensive Definition
Test equating traditionally refers to the
statistical process of determining comparable scores on different
forms of an exam. It can be accomplished using either classical
test theory or item
response theory.
In item response theory, equating is the process
of equating the units and origins of two scales on which the
abilities of students have been estimated from results on different
tests. The process is analogous to equating degrees Fahrenheit with
degrees Celsius by converting measurements from one scale to the
other. The determination of comparable scores is a by-product of
equating that results from equating the scales obtained from test
results.
Why is equating necessary?
Suppose that Dick and Jane both take a test to
become licensed in a certain profession. Because the high
stakes (you get to practice the profession if you pass the
test) may create a temptation to cheat, the organization that
oversees the test creates two forms. If we know that Dick scored
60% on form A and Jane score 70% on form B, do we know for sure
which on has a better grasp of the material? What if form A is
composed of very difficult items, while form B is relatively easy?
Equating analyses are performed to address this very issue, so that
scores are as fair as possible.
Equating in Item Response Theory
In item response theory, person locations are estimated on a scale; i.e. locations are estimated in relation to a unit and origin. It is common in educational assessment to employ tests in order to assess different groups of students with the intention of establishing a common scale by equating the origins, and sometimes units, of the scales obtained from response data from the different tests. The process is referred to as equating or test equating.In item response theory, two different kinds of
equating are horizontal and vertical equating . Vertical equating
refers to the process of equating tests administered to groups of
students with different abilities, such as students in different
grades (years of schooling) . Horizontal equating refers the
equating of tests administered to groups with similar abilities;
for example, two tests administered students in the same grade in
two consecutive calendar years. Different tests are used to avoid
practice effects.
In terms of item response theory, equating is
just a special case of the more general process of scaling,
applicable when more than one test is used. In practice, though,
scaling is often implemented separately for different tests and
then the scales subsequently equated.
A distinction is often made between two methods
of equating; common person and common item equating. Common person
equating involves the administration of two tests to a common group
of persons. The mean and standard deviation of the scale locations
of the groups on the two tests are equated using a linear
transformation. Common item equating involves the use of common
items embedded in two different tests. The mean item location of
the common items is equated.
Classical Approaches to Equating
In classical test theory, mean equating simply adjusts the distribution of scores so that the mean of one form is comparable to the mean of the other form. While mean equating is attractive because of its simplicity, it lacks flexibility, namely accounting for the possibility that the standard deviations of the forms differ.Linear equating adjusts so that the two forms
have a comparable mean and
standard
deviation. There are several types of linear equating that
differ in the assumptions and mathematics used to estimate
parameters. The Tucker and Levine Observed Score methods estimate
the relationship between observed scores on the two forms, while
the Levine True Score method estimates the relationship between
true scores on the two forms.
Equipercentile equating determines the equating
relationship as one where a score could have an equivalent percentile on either form.
This relationship can be nonlinear.
Unlike with item response theory, equating based
on classical test theory is somewhat distinct from scaling.
Equating is a raw-to-raw transformation in that it estimates a raw
score on Form B that is equivalent to each raw score on the base
Form A. Any scaling transformation used is then applied on top of,
or with, the equating.