The Toronto Alexithymia Scale is a measure of deficiency in understanding, processing, or describing emotions. It was developed in 1986 and later revised, removing some of the items. The current version has twenty statements rated on a five-point Likert scale .
27-465: The reliability and validity of the TAS-20 was established by a series of articles by R. Michael Bagby et al. It has been researched extensively. This psychology -related article is a stub . You can help Misplaced Pages by expanding it . Reliability (psychometric) In statistics and psychometrics , reliability is the overall consistency of a measure. A measure is said to have
54-449: A group of test takers, essentially the same results would be obtained. Various kinds of reliability coefficients, with values ranging between 0.00 (much error) and 1.00 (no error), are usually used to indicate the amount of error in the scores." For example, measurements of people's height and weight are often extremely reliable. There are several general classes of reliability estimates: Reliability does not imply validity . That is,
81-402: A high reliability if it produces similar results under consistent conditions: "It is the characteristic of a set of test scores that relates to the amount of random error from the measurement process that might be embedded in the scores. Scores that are highly reliable are precise, reproducible, and consistent from one testing occasion to another. That is, if the testing process were repeated with
108-404: A means of measuring attributes of a person or as a means of predicting scores on a criterion. While a reliable test may provide useful valid information, a test that is not reliable cannot possibly be valid. For example, if a set of weighing scales consistently measured the weight of an object as 500 grams over the true weight, then the scale would be very reliable, but it would not be valid (as
135-414: A probability of 95%. The standard deviation under repeatability conditions is part of precision and accuracy . An attribute agreement analysis is designed to simultaneously evaluate the impact of repeatability and reproducibility on accuracy. It allows the analyst to examine the responses from multiple reviewers as they look at several scenarios multiple times. It produces statistics that evaluate
162-447: A reliable measure that is measuring something consistently is not necessarily measuring what you want to be measured. For example, while there are many reliable tests of specific abilities, not all of them would be valid for predicting, say, job performance. While reliability does not imply validity , reliability does place a limit on the overall validity of a test. A test that is not perfectly reliable cannot be perfectly valid, either as
189-402: Is reasonable to assume that errors are equally likely to be positive or negative, and that they are not correlated with true scores or with errors on other tests. It is assumed that: 1. Mean error of measurement = 0 2. True scores and errors are uncorrelated 3. Errors on different measures are uncorrelated Reliability theory shows that the variance of obtained scores is simply the sum of
216-481: Is reasonable to assume that the effect will not be as strong with alternate forms of the test as with two administrations of the same test. However, this technique has its disadvantages: 3. Split-half method : This method treats the two halves of a measure as alternate forms. It provides a simple solution to the problem that the parallel-forms method faces: the difficulty in developing alternate forms. It involves: The correlation between these two split halves
243-514: Is smaller than a predetermined acceptance criterion. Test–retest variability is practically used, for example, in medical monitoring of conditions. In these situations, there is often a predetermined "critical difference", and for differences in monitored values that are smaller than this critical difference, the possibility of variability as a sole cause of the difference may be considered in addition to, for example, changes in diseases or treatments. The following conditions need to be fulfilled in
270-417: Is that measurement errors are essentially random. This does not mean that errors arise from random processes. For any individual, an error in measurement is not a completely random event. However, across a large number of individuals, the causes of measurement error are assumed to be so varied that measure errors act as random variables. If errors have the essential characteristics of random variables, then it
297-472: Is used in estimating the reliability of the test. This halves reliability estimate is then stepped up to the full test length using the Spearman–Brown prediction formula . There are several ways of splitting a test to estimate reliability. For example, a 40-item vocabulary test could be split into two subtests, the first one made up of items 1 through 20 and the second made up of items 21 through 40. However,
SECTION 10
#1732786646543324-401: Is used to estimate the reliability of the test. This method provides a partial solution to many of the problems inherent in the test-retest reliability method . For example, since the two forms of the test are different, carryover effect is less of a problem. Reactivity effects are also partially controlled; although taking the first test may change responses to the second test. However, it
351-431: The ability of the appraisers to agree with themselves (repeatability), with each other ( reproducibility ), and with a known master or correct value (overall accuracy) for each characteristic – over and over again. Because the same test is administered twice and every test is parallel with itself, differences between scores on the test and scores on the retest should be due solely to measurement error. This sort of argument
378-469: The absence of error. Errors of measurement are composed of both random error and systematic error . It represents the discrepancies between scores obtained on tests and the corresponding true scores. This conceptual breakdown is typically represented by the simple equation: The goal of reliability theory is to estimate errors in measurement and to suggest ways of improving tests so that errors are minimized. The central assumption of reliability theory
405-417: The accuracy of measurement. The basic starting point for almost all theories of test reliability is the idea that test scores reflect the influence of two sorts of factors: 1. Consistency factors: stable characteristics of the individual or the attribute that one is trying to measure. 2. Inconsistency factors: features of the individual or the situation that can affect test scores but have nothing to do with
432-423: The attribute being measured. These factors include: The goal of estimating reliability is to determine how much of the variability in test scores is due to measurement errors and how much is due to variability in true scores ( true value ). A true score is the replicable feature of the concept being measured. It is the part of the observed score that would recur across different measurement occasions in
459-563: The concept of reliability from a single index to a function called the information function . The IRT information function is the inverse of the conditional observed score standard error at any given test score. The goal of estimating reliability is to determine how much of the variability in test scores is due to errors in measurement and how much is due to variability in true scores. Four practical strategies have been developed that provide workable methods of estimating test reliability. 1. Test-retest reliability method : directly assesses
486-704: The degree to which test scores are consistent from one test administration to the next. It involves: The correlation between scores on the first test and the scores on the retest is used to estimate the reliability of the test using the Pearson product-moment correlation coefficient : see also item-total correlation . 2. Parallel-forms method : The key to this method is the development of alternate test forms that are equivalent in terms of content, response processes and statistical characteristics. For example, alternate forms exist for several tests of general intelligence, and these tests are generally seen equivalent. With
513-486: The establishment of repeatability: Repeatability methods were developed by Bland and Altman (1986). If the correlation between separate administrations of the test is high (e.g. 0.7 or higher as in this Cronbach's alpha-internal consistency-table ), then it has good test–retest reliability. The repeatability coefficient is a precision measure which represents the value below which the absolute difference between two repeated test results may be expected to lie with
540-525: The methods to estimate reliability include test-retest reliability , internal consistency reliability, and parallel-test reliability . Each method comes at the problem of figuring out the source of error in the test somewhat differently. It was well known to classical test theorists that measurement precision is not uniform across the scale of measurement. Tests tend to distinguish better for test-takers with moderate trait levels and worse among high- and low-scoring test-takers. Item response theory extends
567-422: The parallel test model it is possible to develop two forms of a test that are equivalent in the sense that a person's true score on form A would be identical to their true score on form B. If both forms of the test were administered to a number of people, differences between scores on form A and form B may be due to errors in measurement only. It involves: The correlation between scores on the two alternate forms
SECTION 20
#1732786646543594-406: The reliability coefficient is defined as the ratio of true score variance to the total variance of test scores. Or, equivalently, one minus the ratio of the variation of the error score and the variation of the observed score : Unfortunately, there is no way to directly observe or calculate the true score, so a variety of methods are used to estimate the reliability of a test. Some examples of
621-415: The responses from the first half may be systematically different from responses in the second half due to an increase in item difficulty and fatigue. In splitting a test, the two halves would need to be as similar as possible, both in terms of their content and in terms of the probable state of the respondent. The simplest method is to adopt an odd-even split, in which the odd-numbered items form one half of
648-421: The returned weight is not the true weight). For the scale to be valid, it should return the true weight of an object. This example demonstrates that a perfectly reliable measure is not necessarily valid, but that a valid measure necessarily must be reliable. In practice, testing measures are never perfectly consistent. Theories of test reliability have been developed to estimate the effects of inconsistency on
675-449: The same conditions of measurement. In other words, the measurements are taken by a single person or instrument on the same item, under the same conditions, and in a short period of time. A less-than-perfect test–retest reliability causes test–retest variability . Such variability can be caused by, for example, intra-individual variability and inter-observer variability . A measurement may be said to be repeatable when this variation
702-402: The test and the even-numbered items form the other. This arrangement guarantees that each half will contain an equal number of items from the beginning, middle, and end of the original test. Test-retest reliability Repeatability or test–retest reliability is the closeness of the agreement between the results of successive measurements of the same measure , when carried out under
729-475: The variance of true scores plus the variance of errors of measurement . This equation suggests that test scores vary as the result of two factors: 1. Variability in true scores 2. Variability due to errors of measurement. The reliability coefficient ρ x x ′ {\displaystyle \rho _{xx'}} provides an index of the relative influence of true and error scores on attained test scores. In its general form,
#542457