Reliability and validity - Wikiversity
Reliability and validity are two concepts that are important for defining and measuring Reliability is stated as correlation between scores of Test 1 and Test 2. We often think of reliability and validity as separate ideas but, in fact, they're One of my favorite metaphors for the relationship between reliability is that of the . As mentioned in Key Concepts, reliability and validity are closely related. To better understand this relationship, let's step out of the world of testing and onto a .
The third scenario shows a case where your hits are spread across the target and you are consistently missing the center. Your measure in this case is neither reliable nor valid.
Finally, we see the "Robin Hood" scenario -- you consistently hit the center of the target. Your measure is both reliable and valid I bet you never thought of Robin Hood in those terms before. Another way we can think about the relationship between reliability and validity is shown in the figure below.
Here, we set up a 2x2 table.
The columns of the table indicate whether you are trying to measure the same or different concepts. The rows show whether you are using the same or different methods of measurement. Imagine that we have two concepts we would like to measure, student verbal and math ability. Furthermore, imagine that we can measure each of these in two ways.
Relation between Validity and Reliability of a Test
Second, we can ask the student's classroom teacher to give us a rating of the student's ability based on their own classroom observation. The first cell on the upper left shows the comparison of the verbal written test score with the verbal written test score. But how can we compare the same measure with itself?
We could do this by estimating the reliability of the written test through a test-retest correlation, parallel forms, or an internal consistency measure See Types of Reliability. What we are estimating in this cell is the reliability of the measure.
Reliability & Validity
The cell on the lower left shows a comparison of the verbal written measure with the verbal teacher observation rating. Because we are trying to measure the same concept, we are looking at convergent validity See Measurement Validity Types. The cell on the upper right shows the comparison of the verbal written exam with the math written exam. Here, we are comparing two different concepts verbal versus math and so we would expect the relationship to be lower than a comparison of the same concept with itself e.
Thus, we are trying to discriminate between two concepts and we would consider this discriminant validity. Finally, we have the cell on the lower right.
Reliability and validity
A test measures consistently, but it may not measure what it intends to measure. For example, when a man wrongly reports his date of birth consistently, it may be reliable but not valid. Relation Validity of a Test: Validity is concerned with the extent to which the purpose of the test is being served. It studies how truthfully the test measures what it purports to measure.
On the other hand, validity is the correlation of the test with some outside external criteria. A test to be valid, has to be reliable. A test which possesses poor reliability is not expected to yield high validity. To be valid a test must be reliable.
Tests with low reliability cannot be highly valid. Validity may be said as correctness of measurement.
If a test is heterogeneous, it has low reliability and high validity. On the other hand, maximum validity requires items differing in difficulty and low inter-correlation among items. The validity of a test may not be higher than the reliability index. Validity is the proportion of common factor variance.
A valid test is always reliable. If a test truthfully measures what it purports to measure is both valid and reliable. For example, when a man truly reports his date of birth consistently, it is both valid and reliable.