Clinically Meaningful Gaps

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
0-6
7-11
12-15
16-41
42-46
47-52
0.65
0.45
0.36
0.30
0.36
0.65

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. … Rasch Measurement Transactions, 2002, 15:4 p. 850



Rasch Publications
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

To be emailed about new material on www.rasch.org
please enter your email address here:

I want to Subscribe: & click below
I want to Unsubscribe: & click below

Please set your SPAM filter to accept emails from Rasch.org

www.rasch.org welcomes your comments:

Your email address (if you want us to reply):

 

ForumRasch 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 3-31, 2015, Fri.-Fri. On-line workshop: Practical Rasch Measurement - Further Topics (E. Smith, Winsteps), www.statistics.com
July 27 - Nov. 20, 2015, Mon.-Fri. On-line course: Introduction to Rasch Measurement Theory (D. Andrich, I. Marais, RUMM), www.education.uwa.edu.au/ppl/courses
Aug. 14 - Sept. 11, 2015, Fri.-Fri. On-line workshop: Many-Facet Rasch Measurement (E. Smith, Facets), www.statistics.com
Aug. 20-24, 2015, Thurs.-Mon. PROMS: Pacific Rim Objective Measurement Symposium 2015, Fukuoka, Japan, proms.promsociety.org/2015/
Sept. 4 - Oct. 16, 2015, Fri.-Fri. On-line workshop: Rasch Applications, Part 1: How to Construct a Rasch Scale (W. Fisher), www.statistics.com
Sept. 9-11, 2015, Wed.-Fri. In-person workshop: Introductory Rasch (A. Tennant, RUMM), Leeds, UK, www.leeds.ac.uk/medicine/rehabmed/psychometric
Sept. 14-16, 2015, Mon.-Wed. IACAT Conference: International Association of Computerized Adaptive Testing, Cambridge, UK, iacat.org
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
Oct. 16 - Nov. 13, 2015, Fri.-Fri. On-line workshop: Practical Rasch Measurement - Core Topics (E. Smith, Winsteps), www.statistics.com
Oct. 23 - Nov. 20, 2015, Fri.-Fri. On-line workshop: Rasch Applications, Part 2: Clinical Assessment, Survey Research, and Educational Measurement (W. Fisher), www.statistics.com
Nov. 13, 2015, Fri. In-person workshop: Rasch Models in Business Administration, in Homage to Professor Pedro Álvarez-Martínez, Tenerife, Canary Islands, www.institutos.ull.es
Dec. 2-4, 2015, Wed.-Fri. In-person workshop: Introductory Rasch (A. Tennant, RUMM), Leeds, UK, www.leeds.ac.uk/medicine/rehabmed/psychometric
March 18, 2016, Fri. UK Rasch User Group Meeting, Durham, UK, www.rasch.org.uk
Aug. 12 - Sept. 9, 2016, Fri.-Fri. On-line workshop: Many-Facet Rasch Measurement (E. Smith, Facets), www.statistics.com
The HTML to add "Coming Rasch-related Events" to your webpage is:
<script type="text/javascript" src="http://www.rasch.org/events.txt"></script>

The URL of this page is www.rasch.org/rmt/rmt154e.htm

Website: www.rasch.org/rmt/contents.htm