Understanding Assessment: Reliability and Validity
After reading this article you will learn about the relation between validity and reliability of a test. Relation # Reliability of a Test: 1. Reliability refers to the. Define reliability, including the different types and how they are assessed. would be relevant to assessing the reliability and validity of a particular measure. Then a score is computed for each set of items, and the relationship between the. 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 .
Imagine that for each person you are measuring, you are taking a shot at the target. If you measure the concept perfectly for a person, you are hitting the center of the target. If you don't, you are missing the center.
The more you are off for that person, the further you are from the center. The figure above shows four possible situations. In the first one, you are hitting the target consistently, but you are missing the center of the target. That is, you are consistently and systematically measuring the wrong value for all respondents.
Reliability & Validity
This measure is reliable, but no valid that is, it's consistent but wrong. The second, shows hits that are randomly spread across the target. You seldom hit the center of the target but, on average, you are getting the right answer for the group but not very well for individuals.
In this case, you get a valid group estimate, but you are inconsistent. Here, you can clearly see that reliability is directly related to the variability of your measure.
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. If at this point your bathroom scale indicated that you had lost 10 pounds, this would make sense and you would continue to use the scale. But if it indicated that you had gained 10 pounds, you would rightly conclude that it was broken and either fix it or get rid of it.
In evaluating a measurement method, psychologists consider two general dimensions: Psychologists consider three types of consistency: Test-Retest Reliability When researchers measure a construct that they assume to be consistent across time, then the scores they obtain should also be consistent across time. For example, intelligence is generally thought to be consistent across time. A person who is highly intelligent today will be highly intelligent next week. This means that any good measure of intelligence should produce roughly the same scores for this individual next week as it does today.
Clearly, a measure that produces highly inconsistent scores over time cannot be a very good measure of a construct that is supposed to be consistent. This is typically done by graphing the data in a scatterplot and computing the correlation coefficient.
But other constructs are not assumed to be stable over time.
Reliability and validity
The very nature of mood, for example, is that it changes. So a measure of mood that produced a low test-retest correlation over a period of a month would not be a cause for concern.
On the Rosenberg Self-Esteem Scale, people who agree that they are a person of worth should tend to agree that they have a number of good qualities.
This is as true for behavioral and physiological measures as for self-report measures. For example, people might make a series of bets in a simulated game of roulette as a measure of their level of risk seeking. Like test-retest reliability, internal consistency can only be assessed by collecting and analyzing data.
This involves splitting the items into two sets, such as the first and second halves of the items or the even- and odd-numbered items. Then a score is computed for each set of items, and the relationship between the two sets of scores is examined.
Reliability and Validity of Measurement – Research Methods in Psychology
For example, there are ways to split a set of 10 items into two sets of five. Interrater Reliability Many behavioral measures involve significant judgment on the part of an observer or a rater.
But how do researchers make this judgment? We have already considered one factor that they take into account—reliability. When a measure has good test-retest reliability and internal consistency, researchers should be more confident that the scores represent what they are supposed to. There has to be more to it, however, because a measure can be extremely reliable but have no validity whatsoever.
Thus, reliability controls validity. Reliability may be said as the dependability of measurement. Maximum reliability is found in case of homogeneous items.
Relation between Validity and Reliability of a Test
Maximum reliability requires items of equal difficulty and high inter- correlation among test items. Validity co-efficient does not exceed the square root of reliability coefficient. The reliability is the proportion of true variance.
We cannot claim that a reliable test is also valid. This may or may not be true. 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.