By Noel P. Munda, LPT, MAEd
January 19, 2022
Validity of Instrument
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 correspond to a different test of the same thing?
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.
In other words, is the test constructed in a way that it successfully tests what it claims to test?
Construct validity is usually verified by comparing the test to other tests that measure similar qualities to see how highly correlated the two measures are.
For example, one way to demonstrate the construct validity of a cognitive aptitude test is by correlating the outcomes on the test to those found on other widely accepted measures of cognitive aptitude.
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.
Expert judgment (not statistics) is the primary method used to determine whether a test has content validity.
Content validity is most often measured by relying on the knowledge of people who are familiar with the construct being measured.
These subject-matter experts are usually provided with access to the measurement tool and are asked to provide feedback on how well each question measures the construct in question. Their feedback is then analyzed, and informed decisions can be made about the effectiveness of each question.
How to perform content validity?
1. Collect data from subject matter experts.
2. Calculate the content validity ratio.
Content Validity Ratio = (ne – N/2) / (N/2)
where:
Ne = The number of subject matter experts indicating “essential”
N = The total number of Subject Matter Expert panelists
If the content validity ratio for a given question falls below a certain critical value, it’s likely that the question is not measuring the construct of interest as well as it should.
The content validity index (CVI), is the mean content validity ratio of all questions on a test. The closer the CVI is to 1, the higher the overall content validity of a test.
FACE VALIDITY
Face validity (or Surface 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.
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.
It is a less technical way of assessing the validity of a test and it’s often used just used as a quick way to detect whether or not a test should be modified in some way before being used.
CRITERION VALIDITY
Criterion validity evaluates how closely the results of your test correspond to the results of a different test.
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.
References:
https://www.spsstests.com/2015/02/how-to-test-validity-questionnaire.html
https://www.scribbr.com/methodology/types-of-validity/?fbclid=IwAR27G-GAz4YpRlQjiUxuXAJj-H3J4XKl45SpV_CSPX8eG_22-1z-Ij046mM
https://www.criteriacorp.com/resources/glossary/construct-validity-0
http://www.mathcs.duq.edu/~packer/Courses/Psy624/test.html
https://study.com/academy/lesson/content-validity-definition-index-examples.html
https://www.statology.org/content-validity/