One of the primary purposes of creating an item bank for adaptive testing is to measure patient health status in a precise and efficient manner. Several decisions are required during the construction of an item bank. One of the most critical is to determine a "real" gap between adjacent items in order to assess the necessity of adding new items in that area.
A commonly used criterion is that a meaningful, i.e., substantively significant, gap is a calibration difference of 0.5 logit or more. While useful psychometrically, this standard may overlook important differences that arise from differences in health status or even disease type. We offer an alternative to the psychometric standard of the 0.5 logit difference, namely clinically important or meaningful differences (CMD). We propose that a gap should be defined as "the calibration difference of two adjacent items equal to or greater than a CMD". In contrast, the gap will be considered negligible if the calibration difference between two adjacent items is less than the value of the CMD. That is, there is no clinical motivation to fill gaps less than the value of the CMD.
|Raw Score Range on FACT-Fatigue||Clinically Meaningful Distance (CMD) in Logits|
The sizes of clinically meaningful gaps vary along the measurement continuum (Hays & Woolley, 2000). As a first step, Cella et al. estimated CMD sizes by triangulating anchor- and distribution-based approaches. They determined that 3 raw score units on the Fatigue subscale of the Functional Assessment of Cancer Therapy (FACT-Fatigue) provide reasonable initial estimates of CMD size all along the continuum. After conversion of the raw score CMD values to logits, we arrived at 4 gap values based upon the location along the fatigue continuum (see Table). These gap sizes provide guidance as to where further items are needed, and will ultimately enhance the clinical relevance of item banking and adaptive testing in health status and quality of life measurement. Better techniques for estimating CMD size are under development.
Jin-shei Lai and David T. Eton.
Center on Outcomes Research and Education (CORE), Evanston Northwestern Healthcare and Northwestern University
Cella, D., Eton, D.T., Lai, J-S., & Peterman, A.H. (in press). Combining anchor and distribution based methods to derive clinically meaningful differences on the Functional Assessment of Cancer Therapy (FACT) anemia and fatigue scales. Journal of Pain & Symptom Management.
Hays, R.D. & Woolley, J.M. (2000). The concept of clinically meaningful difference in health-related quality-of-life research: How meaningful is it? Pharmacoeconomics, 18, pp. 419-423.
Clinically Meaningful Gaps. Lai J.-S., Eton D.T. 15:4 p. 850
Clinically Meaningful Gaps Lai J.-S., Eton D.T. Rasch Measurement Transactions, 2002, 15:4 p. 850
|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 2nd. 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|
|Forum||Rasch Measurement Forum to discuss any Rasch-related topic|
Go to Top of Page
Go to index of all Rasch Measurement Transactions
AERA members: Join the Rasch Measurement SIG and receive the printed version of RMT
Some back issues of RMT are available as bound volumes
Subscribe to Journal of Applied Measurement
Go to Institute for Objective Measurement Home Page. The Rasch Measurement SIG (AERA) thanks the Institute for Objective Measurement for inviting the publication of Rasch Measurement Transactions on the Institute's website, www.rasch.org.
|Coming Rasch-related Events|
|July 25, 2014, Fri.||In-person workshop: Measuring Rehabilitation Outcomes in Older Adults, Chicago, www.rehabmeasures.org|
|July 28 - Nov. 22, 2014, Mon.-Sat..||On-line course: Introduction to Rasch Measurement Theory (D. Andrich, I. Marais) www.education.uwa.edu.au/ppl/courses|
|Aug. 2-6, 2014, Sat.-Wed.||PROMS2014, Guangzhou, China: Sat.-Sun. workshops; Mon.-Wed. symposium, www.confchina.com|
|Aug. 8 - Sept. 5, 2014, Fri.-Fri.||On-line workshop: Many-Facet Rasch Measurement (E. Smith, Facets), www.statistics.com|
|Sept. 3-5, 2014, Wed.-Fri.||IMEKO International Measurement Confederation Symposium, Madeira Island, Portugal, www.imekotc7-2014.pt|
|Sept. 10-12, 2014, Wed.-Fri.||In-person workshop: Introductory Rasch (A. Tennant, RUMM), Leeds, UK, www.leeds.ac.uk/medicine/rehabmed/psychometric|
|Sept. 12 - Oct. 24, 2014, Fri.-Fri.||On-line workshop: Rasch Applications, Part I: How to Construct a Rasch Scale (W.P. Fisher), www.statistics.com|
|Sept. 15-17, 2014, Mon.-Wed.||In-person workshop: Intermediate Rasch (A. Tennant, RUMM), Leeds, UK, www.leeds.ac.uk/medicine/rehabmed/psychometric|
|Sept. 18-19, 2014, Thurs.-Fri.||In-person workshop: Advanced Rasch (A. Tennant, RUMM), Leeds, UK, www.leeds.ac.uk/medicine/rehabmed/psychometric|
|Sept. 30, 2014, Tues.||Submission deadline: 6th Rasch Conference: Sixth International Conference on Probabilistic Models for Measurement in Education, Psychology, Social Science and Health, Cape Town, South Africa www.rasch.co.za/conference.php|
|Oct. 3, 2014, Fri.||Submission deadline: IOMC 2015: International Outcomes Measurement Conference, Chicago IL www.jampress.org|
|Oct. 8-10, 2014, Wed.-Fri.||IACAT Conference: International Association of Computerized Adaptive Testing, Princeton, NJ, iacat.org/conference|
|Oct. 17 - Nov. 14, 2014, Fri.-Fri.||On-line workshop: Practical Rasch Measurement - Core Topics (E. Smith, Winsteps), www.statistics.com|
|Nov. 14, 2014, Fri.||In-person workshop: IX Workshop on Rasch Models in Business Administration, Tenerife, Canary Islands, Spain, www.institutos.ull.es/viewcontent/institutos/iude/46416/es|
|Dec. 3-5, 2014, Wed.-Fri.||In-person workshop: Introductory Rasch (A. Tennant, RUMM), Leeds, UK, www.leeds.ac.uk/medicine/rehabmed/psychometric|
|Jan. 2 - Jan. 30, 2015, Fri.-Fri.||On-line workshop: Practical Rasch Measurement - Core Topics (E. Smith, Winsteps), www.statistics.com|
|Jan. 12-14, 2015, Mon.-Wed.||6th Rasch Conference: Sixth International Conference on Probabilistic Models for Measurement in Education, Psychology, Social Science and Health, Cape Town, South Africa www.rasch.co.za/conference.php|
|March 11-13, 2015, Wed.-Fri.||In-person workshop: Introductory Rasch (A. Tennant, RUMM), Leeds, UK, www.leeds.ac.uk/medicine/rehabmed/psychometric|
|March 20, 2015, Fri.||UK Rasch User Group Meeting, London, United Kingdom, www.rasch.org.uk|
|March 26-27, 2015, Thur.-Fri.||In-person workshop: Introduction to Rasch Measurement with Winsteps (W. Boone), Cincinnati, raschmeasurementanalysis.com|
|April 16-20, 2015, Thurs.-Mon.||AERA Annual Meeting, Chicago IL www.aera.net|
|April 21-22, 2015, Tues.-Wed.||IOMC 2015: International Outcomes Measurement Conference, Chicago IL www.jampress.org|
|May 13-15, 2015, Wed.-Fri.|
|May 18-20, 2015, Mon.-Wed.||In-person workshop: Intermediate Rasch (A. Tennant, RUMM), Leeds, UK, www.leeds.ac.uk/medicine/rehabmed/psychometric|
|Sept. 9-11, 2015, Wed.-Fri.|
|Sept. 14-16, 2015, Mon.-Wed.||In-person workshop: Intermediate Rasch (A. Tennant, RUMM), Leeds, UK, www.leeds.ac.uk/medicine/rehabmed/psychometric|
|Sept. 17-18, 2015, Thur.-Fri.||In-person workshop: Advanced Rasch (A. Tennant, RUMM), Leeds, UK, www.leeds.ac.uk/medicine/rehabmed/psychometric|
|Dec. 2-4, 2015, Wed.-Fri.|
|The HTML to add "Coming Rasch-related Events" to your webpage is:|