Each fall the General and Applied Knowledge (GAK) and Comprehensive Written Section (CWS) examinations are administered to candidates who wish to progress toward Board certification. Both tests are now evaluated using a statistical technique called the Rasch Model, which helps in the evaluation of test results from year to year and can facilitate changes in the two tests. The present article briefly describes the "hows" and "whys" of this statistical technique.
To clarify issues which must be confronted when multiple choice tests are created, administered, evaluated and revised it is well to reflect upon what commonly takes place with the GAK and CWS certification tests. A test is developed utilizing the "Standards for Advanced Education Programs in Pediatric Dentistry," then it is administered to candidates, scoring is completed, and the test is analyzed. Questions flagged through review of selected statistical tests are removed and replaced with new items. Additionally, a percentage of old items are removed and replaced with new material. Maintaining a consistent level of difficulty between the old and new items is critically important. If old items that are difficult are replaced with items that are less difficult, the passing level goes up. If easy items are replaced with more difficult ones, the passing level goes down.
The Rasch Model developed by George Rasch (a Danish mathematician) and utilized by Professor Ben Wright at the University of Chicago helps maintain the same measurement scale from year to year, even if items are removed from a test and new questions are inserted. Maintaining the measurement scale from year to year helps ensure that the same passing point in terms of knowledge level is used, regardless of the mix of items in terms of item difficulty. To build a common measurement scale from one test administration to the next so-called "item anchors" are used. These are in fact the items which are being repeated from one year to the next. As each test is altered from year to year, plots of test takers' performances and test item difficulties are also used to help optimally target new GAK and CWS items so that candidate ability can be accurately and consistently measured.
There are many nuances to the statistics that describe the Rasch model, and a variety of additional ways in which the Rasch model can be utilized. This model is used by many groups in education, in business, and in medicine for the development and maintenance of important tests. In dentistry, the American Dental Association, the American Board of Endodontics, the American Board of Orthodontics and the American Board of Pediatric Dentistry all utilize this model. In summary, the Rasch Model is a robust state of the art analytical technique which currently helps ensure that the same passing point is maintained from year to year, regardless of the mix of items presented on tests of the American Board of Pediatric Dentistry.
William Boone & Stephen Brandt
Excerpted from Boone, William J. & Brandt, Stephen K. Brandt (1999) Analysis of the American Board Examinations Utilizing the Rasch Model. Pediatric Dentistry, 21:2, p. 142
The American Board of Pediatric Dentistry Examinations Boone, W. Rasch Measurement Transactions, 1999, 13:2 p. 689
|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|
|in Spanish:||Análisis de Rasch para todos, Agustín Tristán||Mediciones, Posicionamientos y Diagnósticos Competitivos, Juan Ramón Oreja Rodríguez|
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