One of the most profound benefits of Rasch measurement is the capability of producing a map of the test. The map explains the essence of the instrument. The main purpose of administering psychological tests is to assess the ability level of some trait of the individual in order to make a clinical interpretation or diagnosis. The test should be able to identify the level of functioning, strengths and weaknesses, and implications for interventions. Knox's Cube Test-Revised (Stone MH, Chicago, IL: Stoelting Co, 2002) is one of the few psychological instruments that provide a report form with such capability.
|Click picture for a more readable version|
The Figure shows the sample report form of Socio-Sexual Knowledge and Attitude Test-Revised (SSKAAT-R, Griffith D & Lunsky Y, Chicago, IL: Stoelting Co, 2003). SSKAAT-R is an instrument that measure 6 domains of the sexual knowledge of individual with retardation. Each scale is Rasch analyzed separately. A T-score, a simple linear transformation of the Rasch logits scale, is given which has a mean score of 50 and a standard deviation of 10. The item number on the map indicates the difficulty of an item on T- score scale. This map provides individual item responses and ability estimates of each scale with criterion measures (the mean ability estimate of the different level of mental retardation.) Distance to ceilings and floors can also be examined as it is clear that the, Anatomy and Healthy Boundaries scale has a lower ceiling, not a critical problem in this type of a test. These interpretations can easily be made visually and intuitively from this map. The domain level knowledge can be assessed by examining overall ability and the content level knowledge can be assessed by examining the item response pattern. The clinician does not have to know the value of infit or outfit, just simply examine item response pattern and evaluate the content of the item. For example on figure 1, domain Anatomy has 3 unexpected responses in which items (6, 7, and 8) have similar contents. This is the information clinicians need to know, not the statistical parameter of the individual.
The Rasch property of population invariance, or distribution independence, greatly helps in the analysis of SSKAAT-R data since the target population has a highly skewed distribution (in terms of IQ). A fit analysis assisted to construct statistically appropriate scales. The common Rasch ruler connects items and scores. These are common knowledge in the field of measurement but definitely not for people who actually use the instruments and for those that information is probably of limited importance. The most important thing is to obtain meaningful information from the test without dealing with complex statistical procedures and Rasch measurement has this capability. Certain areas such as early childhood and special education are struggling to find a way to assess child development or to identify learning disability qualification. There is a large gap between people in educational measurement/statistics and practical filed that need to be bridged. A Rasch-assisted report form or the map of the test is an easy way to achieve that goal.
Rasch-assisted Report Form. Yumoto F. Rasch Measurement Transactions, 2003, 16:4 p.893-4
|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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