Internal consistency reflects the extent to which items within an instrument measure various aspects of the same characteristic or construct. Show
DescriptionInternal consistency is a measure of reliability. Reliability refers to the extent to which a measure yields the same number or score each time it is administered, all other things being equal (Hays & Revicki, 2005). Classical test theory views an observed response as consisting of the sum of true score and error (Nunnally & Bernstein, 1994). True score for an individual is assumed to be invariant on repeated measurements. However, two parallel measurements will yield nonidentical observed scores as a result of random error of measurement. Because random errors are normally distributed, the true score will be located at the mean of the distribution of parallel measures. Observed scores actually include true score, systematic error, and random error components.... This is a preview of subscription content, access via your institution. Buying optionsChapter EUR 29.95 Price includes VAT (Singapore)
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Learn about institutional subscriptions Cronbach, L. J. (1951). Coefficient alpha and the internal structure of tests. Psychometrika, 16, 297–334. Google Scholar Feldt, L. S., Woodruff, K. J., & Salih, F. A. (1987). Statistical inference for coefficient alpha. Applied Psychological Measurement, 11, 93–103. Google Scholar Hays, R., & Revicki, D. A. (2005). Reliability and validity (including responsiveness). In P. Fayers & R. Hays (Eds.), Assessing quality of life in clinical trials: Methods and practice (2nd ed., pp. 25–29). New York: Oxford University Press. Google Scholar Nunnally, J. C., & Bernstein, I. C. (1994). Psychometric theory (3rd ed.). New York: McGraw-Hill. Google Scholar Download references Author informationAuthors and Affiliations
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Corresponding authorCorrespondence to Dennis Revicki . Editor informationEditors and Affiliations
Rights and permissionsReprints and Permissions Copyright information© 2014 Springer Science+Business Media Dordrecht About this entryCite this entryRevicki, D. (2014). Internal Consistency Reliability. In: Michalos, A.C. (eds) Encyclopedia of Quality of Life and Well-Being Research. Springer, Dordrecht. https://doi.org/10.1007/978-94-007-0753-5_1494 A measure is reliable if it is consistent, that is, measures the same thing in the same way, each time. explanatory context Questionnaires or structured interview schedules are assumed to be reliable data collection instruments because they ask all respondents a standard set of questions in a given order. Even disregarding the likely possibility of mistakes or deviations from the set of questions by an interviewer or of a respondent reading the questions on a questionnaire in a different order, there is still doubt about the reliability of such data collection instruments. A metric ruler may be reliable as a tool for measuring length as it measures the same thing in the same way, but it is unlikely that a set of questions, which after all relies on communication is reliable in the measurement, for example, of attitudes.
There are various ways of assessing reliability, by far the best is to divide the responses on the test instrument into two groups at random and correlate the answers on each half for the sample. A high correlation coefficient suggests, although by no means confirms, a reliable instrument. For more information on assessing reliability see Researching the Real World Section 1.9.1.1 analytical review Colorado State University (1993–2013) defines the following: Reliability: The extent to which a measure, procedure or instrument yields the same result on repeated trials. Equivalency Reliability: The extent to which two items measure identical concepts at an identical level of difficulty. Stability Reliability: The agreement of measuring instruments over time. Synchronic Reliability: The similarity of observations within the same time frame; it is not about the similarity of things observed. Trochim (2006) states: In research, the term reliability means 'repeatability' or 'consistency'. A measure is considered reliable if it would give us the same result over and over again (assuming that what we are measuring isn't changing!).... There are four general classes of reliability estimates, each of which estimates reliability in a different way. They are: • Inter-Rater or Inter-Observer Reliability Used to assess the degree to which different raters/observers give consistent estimates of the same phenomenon. • Test-Retest Reliability Used to assess the consistency of a measure from one time to another. • Parallel-Forms Reliability Used to assess the consistency of the results of two tests constructed in the same way from the same content domain. • Internal Consistency Reliability Used to assess the consistency of results across items within a test. Wojtczak (2002), in the Glossary of Medical Education Terms, states: Trust in the accuracy or provision of one's results; in the case of tests, it is an expression of the precision, consistency and reproducibility of measurements. Ideally, measurements should be the same when repeated by the same person or made by different assessors. In tests, contributing factors to reliability are the consistency of marking, the quality of test and test items, and the type and size of the sample. Satisfactory reliability of objective tests can be achieved by having large numbers of well-constructed test items marked by computer. Reliability is characterized by the stability, equivalence, and homogeneity of test. Stability or test-retest reliability is the degree to which the same test produces the same results when repeated under the same conditions; Equivalence or alternate-form reliability is the degree to which alternate forms of the same measurement instrument produce the same result; Homogeneity is the extent to which various items legitimately team together to measure a single characteristic, such as a desired attitude. In a clinical examination, obtaining reliability depends on three variables: the students, the examiners and the patients. Such complexity makes it difficult to reproduce a comparable situation for tests of clinical skill and clinical problem-solving. In a reliable assessment procedure, the variability due to the patient and the examiner should be removed. Wherever possible, a subjective approach to marking should be replaced by a more objective one and students should be tested by a number of examiners. It is important to note that students are usually examined using different patients, which may enhance the performance of some students and harm the performance of others. Therefore, tests which aim to assess clinical skills and clinical problem-solving have to contain many samples of student performance if they are to achieve adequate levels of reliability. The development of the multi-station objective structured clinical examination (OSCE) represents an effort to do so. Richard Schaefer (2017): Reliability: The extent to which a measure provides consistent results. associated issues related areas See also validity Researching the Real World Section 1.9 Sources Colorado State University, 1993–2013, Glossary of Key Terms available at http://writing.colostate.edu/guides/guide.cfm?guideid=90,accessed 10 April 2013, still available 1 June 2019. Schaefer, R. T., 2017, 'Glossary' in Sociology: A brief introduction, Fourth Edition, originally c. 2000, McGraw-Hill. Available at http://novellaqalive.mhhe.com/sites/0072435569/student_view0/glossary.html, site dated 2017, accessed 11 June 2017, 'not found' 1 June 2019. Trochim, W.M.K, 2006, 'Types of Reliability', Research Methods Knowledge Base, last revised 20 October 2006, available at http://www.socialresearchmethods.net/kb/reliablt.php, accessed 10 April 2013, still available 28 December 2016, the page is split over two internet pages, most of the quote is now on http://www.socialresearchmethods.net/kb/reltypes.php, accessed 14 June 2019. Wojtczak, A., 2002, Glossary of Medical Education Terms, http://www.iime.org/glossary.htm, December, 2000, Revised February 2002, accessed 19 August 2014, page not available 28 December 2016. Is the extent to which an instrument yields the same results on repeated trials?Reliability is the extent to which an experiment, test, or any measuring procedure yields the same result on repeated trials.
What is the ability of a research instrument to yield consistent results?Reliability refers to the degree to which an instrument yields consistent results. Common measures of reliability include internal consistency, test-retest, and inter-rater reliabilities.
What is meant by reliability of an instrument?The reliability of a measurement instrument is the extent to which it yields consistent, reproducible estimates of what is assumed to be an underlying true score.
Is the extent to which a test or procedure will yield the same results either over time or with different individuals administering the test?11), "reliability is the extent to which an experiment, test or any measuring procedure yields the same results on repeated trials."
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