Psychometrics:
Psychometrics is the field of study
concerned with the theory and technique of psychological measurement which
includes the measurement of knowledge, abilities, attitudes, personality
traits, and educational measurement. The field is primarily concerned with
the construction and validation of measurement instruments such as
questionnaires, tests, and personality assessments. It involves two major
research tasks, namely: (i) the construction of instruments and procedures for
measurement; and (ii) the development and refinement of theoretical approaches
to measurement.
Psychometric Properties:
The psychometric properties of a psychological test
relate to the data that has been collected on the test to determine how well it
measures the construct of interest. In order to develop a good psychological
test, the new test is subjected to statistical analyses to ensure that it has
good psychometric properties.
There are two broad types of psychometric properties
that a test must have in order to be considered a good measure of a particular
construct.
1-Reliability."This is the test's
ability to measure the construct of interest consistently.
Types of Reliability:
1-Test –Retest Reliability: the same test twice a group and correlate the two set of
score. 2- Equivalent- Forms Reliability: correlation between scores on two
forms of the same test taken concurrently, at different times
3- Split-Half Reliability: measure of internal consistency of a test, correlation
between scores on the odd numbered and even number items of a single test. 4- Kuder- Richardson which measure the
internal consistency, used to estimate test reliability from one administration
of test.
5- Scorer Reliability compares
the two scores of the same test by two independent.
2-validity Validity
refers to how well the test accurately measures the construct of interest. "It
is an agreement/relationship between a test score and the quality it is
intended to measure”
Types of validity:
1- Face Validity, the
"appearance" of validity. If all you have is face validity, no
inferences or generalizations can be made of actual behavior.Need to compare
their test responses to actual behavior(i.e., aggressiveness in school). By giving
the test-item to a panel of experts and asking for their judgment onproximity
of the test content with construct of the test. (Face validity)
2-Content-Related Validity: test possesses content validity to the extent that it provides
an adequate representation of construct you are trying to measure.
3- Criterion-Related Validity: how well test can predict relevant
aspects of future behavior you are interested in. Two types of
Criterion-Related Validity:
(a)Predictive Validity the "forecasting" function
of a test. How well can test predict future performance ?Predictor: is score
you obtain on test;
(b) Concurrent Validity. Want
to know how person is behaving now. Tests are taken at same time; designed to
predict person’s current performance (assess simultaneous relationship between
test and criterion)
.4- Construct Validity : Construct validity looks into the
agreement between a theoretical concept and a specific measuring procedure. For
example, where a researcher invents a new instrument that intends to measure IQ
capabilities, the researcher might need to spend time attempting to “define”
intelligence in order to achieve an acceptable level of construct validity.
Construct validity can further be subdivided into convergent validity and
discriminate validity. Convergent validity is a general agreement between
measures where theoretically they should be related. On the other hand,
discriminate validity is a general disagreement between measures where
theoretically they should not be related [16]. Both convergent and discriminate
validities will be examined by using the item-scale correlations; convergent
validity indicates correlation between an item and its own scale, while
discriminate validity indicates correlation between an item and any of the
other scales [17].
Construct
Validity conducted
when you first create a test to measure a construct of interest .Two processes
used to determine construct validity:
a) Convergent Validity new
test needs to correlate well with other tests believed to be measuring same
construct. By administering the test along with other established tests
developed on theoretically similar constructs and examining the correlation
between the two (Convergent validity)
.b) Discriminant Validity (Divergent Validity)you
need to show that your test measures something a bit different from other tests
that purport to measure the same construct (Uniqueness of test).-Why devise new
test if there is already one around. By
administering the test along with theoretically opposite tests and exploring
the correlation (Divergent validity).
3-Internal
consistency:
It indicates
the extent to which items on a test measure the same construct. A high internal
consistency reliability coefficient indicates that the items on the test are
very similar to each other in content (homogeneous). It is important to note
that the length of a test also affects internal consistency. A very long test,
therefore, can spuriously have inflated reliability coefficient. Internal
consistency is commonly measured as Cronbach’sAlpha which is between 0 (low)
and 1 (high).
4-Dimensionality:
a scale’s dimensionality, or factor structure, refers to the
number and nature of the variables reflected in its items. First, they must
understand the number of psychological variables, or dimensions, reflected in
its items. A scale’s items might be uni-dimensional, all reflecting a single
common psychological variable or they might be multidimensional, reflecting two
or more psychological variables. The second core dimensionality issue is, if a
scale is multidimensional, whether the dimensions are correlated with each
other. The third dimensionality issue is, again if a
scale is multidimensional, the psychological meaning of the dimensions.
Researchers must identify the nature of the psychological variables reflected
by the dimensions.
Psychometric Properties Evaluation
Psychometric
properties are defined as the elements that contribute to the statistical
adequacy of
the
instrument in terms of reliability and validity [23]. When both validity and
reliability
analyses
produce reasonably good results, then, the translated questionnaire can be
concluded
and
declared to have acceptable psychometric properties.
5- Test length
Test construction is not just a
simple matter of throwing any kind of item into a main batch. It is crucial to
decide what type of item format is required.
The length of the test should
be suitable for that particular group. It would be a waste of time to test
someone with a major depressive disorder on a test which requires 3 hours of
heavy concentration. In other words, test items can come in different formats
and styles such as multiple-choice questionnaires, true-false items,
forced-choice, closed/open-response and so forth.
Validation: evidence
for the validity of a test comes from demonstrating relationship/correlation
between the test and other attributes it purports to measure. Three types of
validity that need to be demonstrated ;content, criterion & construct. We must have convincing proof that
there is a relationship between our test and what it claims to measure before
we are justified in saying there is this connection and that this test is a
valid measure of what we are interested in.
6-Standardization:
Item selection is never a perfect system. It always involves an
item measurement error in assessment tests .That is why careful consideration
is applied to the planning and implementation of item selection from the
beginning to the end stages to avoid as little as possible too much measurement
error.
1.
Item
analysis phase: The item analysis phase
involves 3 different types of item statistics:1.Item difficulty value 2.discrminationvalue
3.Item total correlation. Item
statistics help the researcher to choose the most suitable items. It is always
wise to try and adapt tests on a homogeneous basis, which means
taking into account many different demographic features of the test person,
such as age, sex, social/economic background, educational status, and most
important cultural differences.
References:-
2.http://bpd.about.com/od/glossary/g/Psychometric-Properties.htm
3 .
http://courseweb.edteched.uottawa.ca/PSY1102C/Lectures/psychometric.htm
4 . http://psych.wfu.edu/furr/716/Furr%20SC&P%20Ch%204%20- %20Dimensionality%20and%20Reliability.pdf
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