Meaning
of validity
Validity refers to
the question: “Does the test measure what it claims to measure”?
The word “valid”
comes from the Latin ‘validus’, it meaning strong. Validity is the accuracy of
test or experiment.
§ Concept of validity given by Kelly (1927) and
defined validity as “a test is valid if it measures what it claims to measure”.
§ Logically, validity is the property of an argument made up
of on the fact- ‘the truth of the hypotheses, guarantees the truth of the
conclusion’.
§ Test Validity refers to the meaning and usefulness of test
results.
§ Validity of an assessment is the degree to which it measures
what it is supposed to measure.
§ More specifically, validity refers to the degree to which a
certain inference or interpretation based on a test is appropriate.
§ Validity of a test means, what the test measures and how
well it does?
Validity tells
you how accurately a method measures something. If a method measures what it
claims to measure, and the results closely correspond to real-world values,
then it can be considered valid. There are four main types of validity:
- Construct
validity: Does the test measure the
concept that it’s intended to measure?
- Content
validity: Is the test fully
representative of what it aims to measure?
- Face validity:
Does the content of the test appear to be suitable to its aims?
- Criterion
validity: Do the
results accurately measure the concrete outcome they are designed to
measure?
In quantitative
research, you have to consider the reliability and
validity of your methods and
measurements.
Construct validity
Construct validity evaluates
whether a measurement tool really represents the thing we are interested in
measuring. It’s central to establishing the overall validity of a method.
What is a construct?
A construct refers to a concept or
characteristic that can’t be directly observed, but can be measured by observing
other indicators that are associated with it.
Constructs can be characteristics of
individuals, such as intelligence, obesity, job satisfaction, or depression;
they can also be broader concepts applied to organizations or social groups,
such as gender equality, corporate social responsibility, or freedom of speech.
Example
There is no
objective, observable entity called “depression” that we can measure directly.
But based on existing psychological research and theory, we can measure
depression based on a collection of symptoms and indicators, such as low
self-confidence and low energy levels.
What is construct validity?
Construct validity is about
ensuring that the method of measurement matches the construct you want to
measure. If you develop a questionnaire to diagnose depression, you need to
know: does the questionnaire really measure the construct of depression? Or is
it actually measuring the respondent’s mood, self-esteem, or some other
construct?
To achieve construct validity, you
have to ensure that your indicators and measurements are carefully developed
based on relevant existing knowledge. The questionnaire must include only
relevant questions that measure known indicators of depression.
The other types of validity
described below can all be considered as forms of evidence for construct
validity.
Content validity
Content validity assesses
whether a test is representative of all aspects of the construct.
To produce valid results, the
content of a test, survey or measurement method must cover all relevant parts
of the subject it aims to measure. If some aspects are missing from the
measurement (or if irrelevant aspects are included), the validity is threatened
and the research is likely suffering from omitted variable bias.
Example
A mathematics
teacher develops an end-of-semester algebra test for her class. The test should
cover every form of algebra that was taught in the class. If some types of
algebra are left out, then the results may not be an accurate indication of
students’ understanding of the subject. Similarly, if she includes questions
that are not related to algebra, the results are no longer a valid measure of
algebra knowledge.
Face validity
Face validity considers how suitable the
content of a test seems to be on the surface. It’s similar to content validity,
but face validity is a more informal and subjective assessment.
Example
You create
a survey to measure the regularity of people’s dietary habits. You review the
survey items, which ask questions about every meal of the day and snacks eaten
in between for every day of the week. On its surface, the survey seems like a
good representation of what you want to test, so you consider it to have high
face validity.
As face validity is a subjective
measure, it’s often considered the weakest form of validity. However, it can be
useful in the initial stages of developing a method.
Criterion validity
Criterion validity evaluates how well
a test can predict a concrete outcome, or how well the results of your test approximate
the results of another test.
What is a criterion variable?
A criterion variable is an
established and effective measurement that is widely considered valid,
sometimes referred to as a “gold standard” measurement. Criterion variables can
be very difficult to find.
What is criterion validity?
To evaluate criterion validity, you
calculate the correlation between the results of your
measurement and the results of the criterion measurement. If there is a high
correlation, this gives a good indication that your test is measuring what it
intends to measure.
Example
A
university professor creates a new test to measure applicants’ English writing
ability. To assess how well the test really does measure students’ writing
ability, she finds an existing test that is considered a valid measurement of
English writing ability, and compares the results when the same group of
students take both tests. If the outcomes are very similar, the new test has
high criterion validity
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