The term validity refers to whether or not a test measures what it intends to measure .
On a test with high validity the items will be closely linked to the test’s intended focus. For many certification and licensure tests this means that the items will be highly related to a specific job or occupation. If a test has poor validity then it does not measure the job-related content and competencies it ought to.
There are several ways to estimate the validity of a test, including content validity, construct validity, criterion-related validity ( concurrent & predictive ) and face validity.
Content validity refers to the connections between the test items and the subject-related tasks. The test should evaluate only the content related to the field of study in a manner sufficiently representative, relevant, and comprehensible .
It implies using the construct correctly (concepts, ideas, notions). Construct validity seeks agreement between a theoretical concept and a specific measuring device or procedure. For example, a test of intelligence nowadays must include measures of multiple intelligences, rather than just logical-mathematical and linguistic ability measures.
Also referred to as instrumental validity , it states that the criteria should be clearly defined by the teacher in advance. It has to take into account other teachers´ criteria to be standardized and it also needs to demonstrate the accuracy of a measure or procedure compared to another measure or procedure which has already been demonstrated to be valid.
Concurrent validity is a statistical method using correlation, rather than a logical method.
Examinees who are known to be either masters or non-masters on the content measured by the test are identified before the test is administered. Once the tests have been scored, the relationship between the examinees’ status as either masters or non-masters and their performance (i.e., pass or fail) is estimated based on the test. This type of validity provides evidence that the test is classifying examinees correctly. The stronger the correlation is, the greater the concurrent validity of the test is.
This is another statistical approach to validity that estimates the relationship of test scores to an examinee's future performance as a master or non-master. Predictive validity considers the question, "How well does the test predict examinees' future status as masters or non-masters?" For this type of validity, the correlation that is computed is based on the test results and the examinee’s later performance. This type of validity is especially useful for test purposes such as selection or admissions.
Like content validity, face validity is determined by a review of the items and not through the use of statistical analyses. Unlike content validity, face validity is not investigated through formal procedures. Instead, anyone who looks over the test, including examinees, may develop an informal opinion as to whether or not the test is measuring what it is supposed to measure. While it is clearly of some value to have the test appear to be valid, face validity alone is insufficient for establishing that the test is measuring what it claims to measure.
Reliability is the extent to which an experiment, test, or any measuring procedure shows the same result on repeated trials. Without the agreement of independent observers able to replicate research procedures, or the ability to use research tools and procedures that produce consistent measurements, researchers would be unable to satisfactorily draw conclusions, formulate theories, or make claims about the generalizability of their research. For researchers, four key types of reliability are:
Equivalency reliability is the extent to which two items measure identical concepts at an identical level of difficulty. Equivalency reliability is determined by relating two sets of test scores to one another to highlight the degree of relationship or association. For example, a researcher studying university English students happened to notice that when some students were studying for finals, they got sick. Intrigued by this, the researcher attempted to observe how often, or to what degree, these two behaviors co-occurred throughout the academic year. The researcher used the results of the observations to assess the correlation between “studying throughout the academic year” and “getting sick”. The researcher concluded there was poor equivalency reliability between the two actions. In other words, studying was not a reliable predictor of getting sick.
Stability reliability (sometimes called test, re-test reliability ) is the agreement of measuring instruments over time. To determine stability, a measure or test is repeated on the same subjects at a future date. Results are compared and correlated with the initial test to give a measure of stability. This method of evaluating reliability is appropriate only if the phenomenon that the test measures is known to be stable over the interval between assessments. The possibility of practice effects should also be taken into account.
Internal consistency is the extent to which tests or procedures assess the same characteristic, skill or quality. It is a measure of the precision between the measuring instruments used in a study. This type of reliability often helps researchers interpret data and predict the value of scores and the limits of the relationship among variables. For example, analyzing the internal reliability of the items on a vocabulary quiz will reveal the extent to which the quiz focuses on the examinee’s knowledge of words.
Inter-rater reliability is the extent to which two or more individuals (coders or raters) agree. Inter-rater reliability assesses the consistency of how a measuring system is implemented. For example, when two or more teachers use a rating scale with which they are rating the students’ oral responses in an interview (1 being most negative, 5 being most positive). If one researcher gives a "1" to a student response, while another researcher gives a "5," obviously the inter-rater reliability would be inconsistent. Inter-rater reliability is dependent upon the ability of two or more individuals to be consistent. Training, education and monitoring skills can enhance inter-rater reliability.
Intra-rater reliability is a type of reliability assessment in which the same assessment is completed by the same rater on two or more occasions. These different ratings are then compared, generally by means of correlation. Since the same individual is completing both assessments, the rater's subsequent ratings are contaminated by knowledge of earlier ratings.
Backwash effect (also known as washback) is the influence of testing on teaching and learning. It is also the potential impact that the form and content of a test may have on learners’ conception of what is being assessed (language proficiency) and what it involves. Therefore, test designers, delivers and raters have a particular responsibility, considering that the testing process may have a substantial impact, either positive or negative.