Validity investigation

Question: I really want to you to help me in a simple explanation understand how in practice can I go about collecting validity evidences via Rasch Analysis with Winsteps to support use and inference of my test?

Answer: There are many types of validity described in the literature, but they summarize to two main topics:

1. Construct validity: does the test measure what it is intended to measure?

2. Predictive validity: does the test produce measures which correspond to what we know about the persons?

Investigation of these validities is performed directly by inspection of the results of the analysis (Rasch or Classical or ...), or indirectly through correlations of the Rasch measures (or raw scores, etc.) with other numbers which are thought to be good indicators of what we want.

Question: That is what exactly type of validity questions should I ask and how can I answer them using Rasch analysis?

Answer: 1. Construct validity: we need a "construct theory" (i.e., some idea about our latent variable) - we need to state explicitly, before we do our analysis, what will be a more-difficult item, and what will be a less-difficult item.

Certainly we can all do that with arithmetic items: 2+2=? is easy. 567856+97765=? is hard.

If the Table 1 item map agrees with your statement. Then the test has "construct validity". It is measuring what you intended to measure.

2. Predictive validity: we need to we need to state explicitly, before we do our analysis, what will be a the characteristics of a person with a higher measure, and what will be the characteristics of a person with a lower measure. And preferably code these into the person labels in our Winsteps control file.

For arithmetic, we expect older children, children in higher grades, children with better nutrition, children with fewer developmental or discipline problems, etc. to have higher measures. And the reverse for lower measures.

If the Table 1 person map agrees with your statement. Then the test has "predictive validity". It is "predicting" what we expected it to predict. (In statistics, "predict" doesn't mean "predict the future", "predict" means predict some numbers obtained by other means.

Question: More specifically, in using, for example, DIF analysis via Winsteps what type of validity question I am trying to answer?

Answer: 1. Construct validity: DIF implies that the item difficulty is different for different groups. The meaning of the construct has changed! Perhaps the differences are too small to matter. Perhaps omitting the DIF item will solve the problem. Perhaps making the DIF item into two items will solve the problem.

For instance, questions about "snow" change their difficulty. In polar countries they are easy. In tropical countries they are difficult. When we discover this DIF, we would define this as two different items, and so maintain the integrity of the "weather-knowledge" construct.

2. Predictive validity: DIF implies that the predictions made for one group of persons, based on their measures, differs from the predictions made for another group. Do the differences matter? Do we need separate measurement systems? ...

Question: Similarly, in using Fit statistics, dimensionality, and order of item difficulty what type of validity questions I am attempting to answer via Winsteps?

Answer: They are the same questions every time. Construct Validity and Predictive Validity. Is there a threat to validity? Is it big enough to matter in a practical way? What is the most effective way of lessening or eliminating the threat?


Help for Winsteps Rasch Measurement Software: www.winsteps.com. Author: John Michael Linacre

For more information, contact info@winsteps.com or use the Contact Form
 

Facets Rasch measurement software. Buy for $149. & site licenses. Freeware student/evaluation download
Winsteps Rasch measurement software. Buy for $149. & site licenses. Freeware student/evaluation download

State-of-the-art : single-user and site licenses : free student/evaluation versions : download immediately : instructional PDFs : user forum : assistance by email : bugs fixed fast : free update eligibility : backwards compatible : money back if not satisfied
 
Rasch, Winsteps, Facets online Tutorials

 

Forum Rasch Measurement Forum to discuss any Rasch-related topic

Click here to add your email address to the Winsteps and Facets email list for notifications.

Click here to ask a question or make a suggestion about Winsteps and Facets software.

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 with Raters and Rating Scales: Rasch Models for Rater-Mediated Assessments, George Engelhard, Jr. & Stefanie Wind 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
Winsteps Tutorials Facets Tutorials Rasch Discussion Groups

 


 

 
Coming Rasch-related Events
Jan. 5 - Feb. 2, 2018, Fri.-Fri. On-line workshop: Practical Rasch Measurement - Core Topics (E. Smith, Winsteps), www.statistics.com
Jan. 10-16, 2018, Wed.-Tues. In-person workshop: Advanced Course in Rasch Measurement Theory and the application of RUMM2030, Perth, Australia (D. Andrich), Announcement
Jan. 17-19, 2018, Wed.-Fri. Rasch Conference: Seventh International Conference on Probabilistic Models for Measurement, Matilda Bay Club, Perth, Australia, Website
Jan. 22-24, 2018, Mon-Wed. In-person workshop: Rasch Measurement for Everybody en español (A. Tristan, Winsteps), San Luis Potosi, Mexico. www.ieia.com.mx
April 10-12, 2018, Tues.-Thurs. Rasch Conference: IOMW, New York, NY, www.iomw.org
April 13-17, 2018, Fri.-Tues. AERA, New York, NY, www.aera.net
May 22 - 24, 2018, Tues.-Thur. EALTA 2018 pre-conference workshop (Introduction to Rasch measurement using WINSTEPS and FACETS, Thomas Eckes & Frank Weiss-Motz), https://ealta2018.testdaf.de
May 25 - June 22, 2018, Fri.-Fri. On-line workshop: Practical Rasch Measurement - Core Topics (E. Smith, Winsteps), www.statistics.com
June 27 - 29, 2018, Wed.-Fri. Measurement at the Crossroads: History, philosophy and sociology of measurement, Paris, France., https://measurement2018.sciencesconf.org
June 29 - July 27, 2018, Fri.-Fri. On-line workshop: Practical Rasch Measurement - Further Topics (E. Smith, Winsteps), www.statistics.com
July 25 - July 27, 2018, Wed.-Fri. Pacific-Rim Objective Measurement Symposium (PROMS), (Preconference workshops July 23-24, 2018) Fudan University, Shanghai, China "Applying Rasch Measurement in Language Assessment and across the Human Sciences" www.promsociety.org
Aug. 10 - Sept. 7, 2018, Fri.-Fri. On-line workshop: Many-Facet Rasch Measurement (E. Smith, Facets), www.statistics.com
Sept. 3 - 6, 2018, Mon.-Thurs. IMEKO World Congress, Belfast, Northern Ireland www.imeko2018.org
Oct. 12 - Nov. 9, 2018, Fri.-Fri. On-line workshop: Practical Rasch Measurement - Core Topics (E. Smith, Winsteps), www.statistics.com

 

 

Our current URL is www.winsteps.com

Winsteps® is a registered trademark
 


 
Concerned about aches, pains, youthfulness? Mike and Jenny suggest Liquid Biocell