Understanding Assessment: Reliability and Validity
Here, I want to show you two ways you can think about their relationship. One of my favorite metaphors for the relationship between reliability is that of the target. After reading this article you will learn about the relation between validity and 4 . Reliability is a prerequisite of validity. A highly reliable test is always a valid. “For a test to be valid, or truthful, it must first be reliable.” (educational assessment ). For example, if you are measuring the reading levels of students after a new.
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. 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. The cell on the lower left shows a comparison of the verbal written measure with the verbal teacher observation rating.
Social Research Methods - Knowledge Base - Reliability & Validity
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. Other areas of theatre such as lighting, sound, functions of stage managers should all be included.
The assessment should reflect the content area in its entirety. What are some ways to improve validity? Make sure your goals and objectives are clearly defined and operationalized.
Expectations of students should be written down. Match your assessment measure to your goals and objectives. Additionally, have the test reviewed by faculty at other schools to obtain feedback from an outside party who is less invested in the instrument.
Get students involved; have the students look over the assessment for troublesome wording, or other difficulties. If possible, compare your measure with other measures, or data that may be available. Standards for educational and psychological testing. Methods in Behavioral Research 7th ed. Educational Measurement 2nd ed. American Council on Education.
Reliability and validity
The Center for the Enhancement of Teaching. Before deciding to use a test, read the test manual and any independent reviews to determine if its reliability is acceptable. The acceptable level of reliability will differ depending on the type of test and the reliability estimate used. The discussion in Table 2 should help you develop some familiarity with the different kinds of reliability estimates reported in test manuals and reviews.
Types of Reliability Estimates Test-retest reliability indicates the repeatability of test scores with the passage of time. This estimate also reflects the stability of the characteristic or construct being measured by the test.
Some constructs are more stable than others. For example, an individual's reading ability is more stable over a particular period of time than that individual's anxiety level. Therefore, you would expect a higher test-retest reliability coefficient on a reading test than you would on a test that measures anxiety.
For constructs that are expected to vary over time, an acceptable test-retest reliability coefficient may be lower than is suggested in Table 1. Alternate or parallel form reliability indicates how consistent test scores are likely to be if a person takes two or more forms of a test. A high parallel form reliability coefficient indicates that the different forms of the test are very similar which means that it makes virtually no difference which version of the test a person takes.
On the other hand, a low parallel form reliability coefficient suggests that the different forms are probably not comparable; they may be measuring different things and therefore cannot be used interchangeably. Inter-rater reliability indicates how consistent test scores are likely to be if the test is scored by two or more raters. On some tests, raters evaluate responses to questions and determine the score. Differences in judgments among raters are likely to produce variations in test scores.
A high inter-rater reliability coefficient indicates that the judgment process is stable and the resulting scores are reliable.
Inter-rater reliability coefficients are typically lower than other types of reliability estimates. However, it is possible to obtain higher levels of inter-rater reliabilities if raters are appropriately trained. Internal consistency reliability indicates the extent to which items on a test measure the same thing.
A high internal consistency reliability coefficient for a test 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 can affect internal consistency reliability. For example, a very lengthy test can spuriously inflate the reliability coefficient. Tests that measure multiple characteristics are usually divided into distinct components.
Reliability and Validity
Manuals for such tests typically report a separate internal consistency reliability coefficient for each component in addition to one for the whole test. Test manuals and reviews report several kinds of internal consistency reliability estimates. Each type of estimate is appropriate under certain circumstances.
The test manual should explain why a particular estimate is reported. Standard error of measurement Test manuals report a statistic called the standard error of measurement SEM. It gives the margin of error that you should expect in an individual test score because of imperfect reliability of the test. The SEM represents the degree of confidence that a person's "true" score lies within a particular range of scores.
For example, an SEM of "2" indicates that a test taker's "true" score probably lies within 2 points in either direction of the score he or she receives on the test. This means that if an individual receives a 91 on the test, there is a good chance that the person's "true" score lies somewhere between 89 and The SEM is a useful measure of the accuracy of individual test scores. The smaller the SEM, the more accurate the measurements.
When evaluating the reliability coefficients of a test, it is important to review the explanations provided in the manual for the following: Types of reliability used.
The manual should indicate why a certain type of reliability coefficient was reported. The manual should also discuss sources of random measurement error that are relevant for the test. How reliability studies were conducted. The manual should indicate the conditions under which the data were obtained, such as the length of time that passed between administrations of a test in a test-retest reliability study.
In general, reliabilities tend to drop as the time between test administrations increases. The characteristics of the sample group. The manual should indicate the important characteristics of the group used in gathering reliability information, such as education level, occupation, etc.
This will allow you to compare the characteristics of the people you want to test with the sample group. If they are sufficiently similar, then the reported reliability estimates will probably hold true for your population as well. Appendix A lists some possible sources. Test validity Validity is the most important issue in selecting a test. Validity refers to what characteristic the test measures and how well the test measures that characteristic.