William McCown and Judith Johnson (Psychological Reports, October 1991, 69, 543-549) describe the unsatisfactory nature of the more than 40 questionnaires developed to ascertain HIV knowledge and prevention skills. They endeavor to produce a better questionnaire: "A useful HIV knowledge test should have a number of characteristics. It should be brief so it can be used quickly by the physician or mental health professional. Optimally, such a test would be reliable and valid across a variety of populations. For example, it should require minimum education, literacy, or intellectual functioning on the part of the examinee. It should also include an oral and written form, both of which should be scorable by persons with limited training" (p. 544).
With input from medical personnel, health educators and special education instructors, 19 open-ended items were constructed, written to be understood by mildly mentally retarded people. A scoring key was composed for each item. 1092 visitors to patients in three hospitals took the test. Responses not clearly showing knowledge were scored incorrect.
The Rasch model was used because it produces item calibrations that are "relatively sample-free or applicable across diverse groups" through 1) examining the internal consistency of a scale regardless of sample variance, and 2) identifying item-sample interactions which threaten comparisons across populations. The analysis was conducted with the RASCAL program.
Item text and chi-square fit statistics are listed in the journal for the 13 of 19 items that showed satisfactory fit. The item showing the most coherence with overall HIV knowledge is "Tell me some ways you do not get HIV disease" [Correct if subject can generate two or more answers]. The least coherent of the 13 fitting items is "What two things should you do if you have the HIV infection?" [Avoid sex with non-infected partner and get medical treatment]. This suggests that an initial analysis of the answers of the first 50 or 100 respondents would have pointed out which items require revision. This could have substantially improved the questionnaire administered to the remaining 1000. Further understanding of the possible HIV knowledge variable is hampered because no item calibrations nor details of misfitting items nor summary of the performance of the respondents are provided.
Basic HIV Disease Knowledge Questionnaire, W McCown & J Johnson Rasch Measurement Transactions, 1992, 6:2 p. 221
|Rasch Measurement Transactions (free, online)||Rasch Measurement research papers (free, online)||Probabilistic Models for Some Intelligence and Attainment Tests, Georg Rasch||Applying the Rasch Model 3rd. Ed., Bond & Fox||Best Test Design, Wright & Stone|
|Rating Scale Analysis, Wright & Masters||Introduction to Rasch Measurement, E. Smith & R. Smith||Introduction to Many-Facet Rasch Measurement, Thomas Eckes||Invariant Measurement: Using Rasch Models in the Social, Behavioral, and Health Sciences, George Engelhard, Jr.||Statistical Analyses for Language Testers, Rita Green|
|Rasch Models: Foundations, Recent Developments, and Applications, Fischer & Molenaar||Journal of Applied Measurement||Rasch models for measurement, David Andrich||Constructing Measures, Mark Wilson||Rasch Analysis in the Human Sciences, Boone, Stave, Yale|
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