(Incidentally, criticisms of standardized tests such as GRE, SAT, etc. A tape measure or set of scales which are incorrectly calibrated will always give the.How to Determine the Validity and Reliability of an Instrumentthe predictive validity of the test and only needs to hire those who score high on her test. This type of reliability test has a disadvantage caused by memory effects.In practice, an assessment is rarely totally valid or totally reliable. Then, comparing the responses at the two time points. This involves giving the questionnaire to the same group of respondents at a later point in time and repeating the research. Reliability is assessed by Test-retest reliability.
Internal consistency reliability looks at the consistency of the score of individual items on an instrument, with the scores of a set of items, or subscale, which typically consists of several items to measure a single construct. Common measures of reliability include internal consistency, test-retest, and inter-rater reliabilities. A common measurement of this type of validity is the correlation coefficient between two measures.Often times, when developing, modifying, and interpreting the validity of a given instrument, rather than view or test each type of validity individually, researchers and evaluators test for evidence of several different forms of validity, collectively (e.g., see Samuel Messick’s work regarding validity).Reliability refers to the degree to which an instrument yields consistent results. Criterion-related validity indicates the extent to which the instrument’s scores correlate with an external criterion (i.e., usually another measurement from a different instrument) either at present ( concurrent validity) or in the future ( predictive validity). Common methods to assess construct validity include, but are not limited to, factor analysis, correlation tests, and item response theory models (including Rasch model). Construct validity indicates the extent to which a measurement method accurately represents a construct (e.g., a latent variable or phenomena that can’t be measured directly, such as a person’s attitude or belief) and produces an observation, distinct from that which is produced by a measure of another construct.
A similar type of reliability called alternate forms, involves using slightly different forms or versions of an instrument to see if different versions yield consistent results. Unlike pre-post tests, no treatment occurs between the first and second administrations of the instrument, in order to test-retest reliability. Test-retest measures the correlation between scores from one administration of an instrument to another, usually within an interval of 2 to 3 weeks. Group variability, score reliability, number of items, sample sizes, and difficulty level of the instrument also can impact the Cronbach’s alpha value.
However, even when using these instruments, you should re-check validity and reliability, using the methods of your study and your own participants’ data before running additional statistical analyses. Therefore, when available, I suggest using already established valid and reliable instruments, such as those published in peer-reviewed journal articles. Kappa statistics, correlation coefficients, and intra-class correlation (ICC) coefficient are some of the commonly reported measures of inter-rater reliability.Developing a valid and reliable instrument usually requires multiple iterations of piloting and testing which can be resource intensive. Common situations where more than one rater is involved may occur when more than one person conducts classroom observations, uses an observation protocol or scores an open-ended test, using a rubric or other standard protocol.
Reliability and Validity Assessment. Carmines, E., & Zeller, R. New York, NY: Harper & Row.
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