# Proper Measurement is "Universally Reproducible"

The late John A. Simpson was a physicist and metrologist associated with the University of Chicago, the Enrico Fermi Institute, and the US National Institute for Standards and Technology.

In the following definition of measurement, taken from the Metrology subject heading in the Encyclopedia of Physics, note that Simpson makes repeated explicit references to the concept of quantity without specifically invoking any tests of additivity or divisibility, though these, along with other similar tests, are indeed implicit in the concept of a "continuous scale of magnitude."

Simpson places far more emphasis on common units, and common methods of obtaining them and determining ordinal relations, than he does on knowing how and when additive relations have been established. He goes so far as to hold that "a proper measurement" is one that is "universally reproducible" "wherever and whenever the measurement process is repeated."

Psychometricians might then do well to shift some of their resources toward deployment of common units and methods for each major measurable variable, and away from the generation of ever more different units and methods. In what follows, the emphasis is mine.

William Fisher

Simpson, J. A. (1991). Metrology. In R. G. Lerner & G. L. Trigg (Eds.), Encyclopedia of physics, 2d Ed. (pp. 723-5). New York, New York: VCH Publishers, Inc.

p. 723-4: "A measurement is a series of manipulations of physical objects or systems according to defined protocols that result in a number. The objects or systems involved are test objects, measuring devices, and computational operations. The objects and devices exist in and are influenced by some environment. The value obtained is purported to represent uniquely the magnitude, or intensity, of some quantity embodied in the test object. This number is acquired to form the basis of a decision affecting some human goal or satisfying some human need that depends on the properties of the test object.

In order to attain this goal of useful decision making, metrology has focused on the task of assuring that the value obtained for a given quantity of a given object is functionally identical wherever and whenever the measurement process is repeated. Only then can all parties to the decision work from a concordant data base. Such a universally reproducible measurement is called a proper measurement.

An analysis of the logical conditions that must be satisfied to achieve a proper measurement shows that three independent arbitrary axioms must be universally agreed upon:

1. All parties must agree upon and have access to a common unit in which the results will be expressed.

2. There must be an agreed-upon physically realizable method of obtaining a continuous scale of magnitude based on the unit.

3. There must be an agreed-upon physically realizable method of determining when the quantity of interest, as embodied in a physical object or system, is equal to, less than, or greater than, some fixed point on this realized scale.

The principal activity of metrologists consists of generating, propagating, testing, and applying to an object or system of interest sets of these measurement axioms for all quantities and all useful magnitudes of those quantities...

Fundamental to the success of such a system is the development, at each transfer [points through which the unit is traceable to the reference standard from secondary standards and the point of use], of realistic estimates of uncertainty."

p. 725: "By far the greatest activity in metrology is that performed in the service of quality control. Manufacturing establishments of any size maintain standards laboratories and/or metrology laboratories. The laboratories maintain the company master standards, gauges, and measuring instruments, which are periodically calibrated against the national standards. The working measuring equipment on the shop floor is calibrated by the metrology laboratory on a scheduled basis. ... In this manner the measurements made for quality control are considered `traceable' to national standards."

William P. Fisher, Jr.

"Measurement lies at the heart of genuine quality improvement, the kind that healthcare organizations undertake on behalf of their patients and communities, not simply to ensure accreditation. When delivery systems get ready to transition from talking about continuous quality improvement to really practicing it, learning to measure and manage care processes and outcomes becomes the first priority. If quality is Job One, measurement is Job Zero."
Carl Stevens, M.D. (UCLA Medical Center) in the Foreword to Statistical Process Control for Healthcare, Marilyn K. Hart & Robert F. Hart, Brooks Cole, 2001

And it is now agreed that measurement is not merely, as S.S. Stevens mistakenly leads people to believe, the arbitrary assignment of numbers to observations.

William P. Fisher, Jr.

Proper Measurement is Universally Reproducible, Fisher W.P. Jr., … Rasch Measurement Transactions, 2004, 18:1 p.967

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

 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
March 31, 2017, Fri. Conference: 11th UK Rasch Day, Warwick, UK, www.rasch.org.uk
April 2-3, 2017, Sun.-Mon. Conference: Validity Evidence for Measurement in Mathematics Education (V-M2Ed), San Antonio, TX, Information
April 26-30, 2017, Wed.-Sun. NCME, San Antonio, TX, www.ncme.org - April 29: Ben Wright book
April 27 - May 1, 2017, Thur.-Mon. AERA, San Antonio, TX, www.aera.net
May 26 - June 23, 2017, Fri.-Fri. On-line workshop: Practical Rasch Measurement - Core Topics (E. Smith, Winsteps), www.statistics.com
June 30 - July 29, 2017, Fri.-Fri. On-line workshop: Practical Rasch Measurement - Further Topics (E. Smith, Winsteps), www.statistics.com
July 31 - Aug. 3, 2017, Mon.-Thurs. Joint IMEKO TC1-TC7-TC13 Symposium 2017: Measurement Science challenges in Natural and Social Sciences, Rio de Janeiro, Brazil, imeko-tc7-rio.org.br
Aug. 7-9, 2017, Mon-Wed. In-person workshop and research coloquium: Effect size of family and school indexes in writing competence using TERCE data (C. Pardo, A. Atorressi, Winsteps), Bariloche Argentina. Carlos Pardo, Universidad Catòlica de Colombia
Aug. 7-9, 2017, Mon-Wed. PROMS 2017: Pacific Rim Objective Measurement Symposium, Sabah, Borneo, Malaysia, proms.promsociety.org/2017/
Aug. 10, 2017, Thurs. In-person Winsteps Training Workshop (M. Linacre, Winsteps), Sydney, Australia. www.winsteps.com/sydneyws.htm
Aug. 11 - Sept. 8, 2017, Fri.-Fri. On-line workshop: Many-Facet Rasch Measurement (E. Smith, Facets), www.statistics.com
Aug. 18-21, 2017, Fri.-Mon. IACAT 2017: International Association for Computerized Adaptive Testing, Niigata, Japan, iacat.org
Sept. 15-16, 2017, Fri.-Sat. IOMC 2017: International Outcome Measurement Conference, Chicago, jampress.org/iomc2017.htm
Oct. 13 - Nov. 10, 2017, Fri.-Fri. On-line workshop: Practical Rasch Measurement - Core Topics (E. Smith, Winsteps), www.statistics.com
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
May 25 - June 22, 2018, Fri.-Fri. On-line workshop: Practical Rasch Measurement - Core Topics (E. Smith, Winsteps), www.statistics.com
June 29 - July 27, 2018, Fri.-Fri. On-line workshop: Practical Rasch Measurement - Further Topics (E. Smith, Winsteps), www.statistics.com
Aug. 10 - Sept. 7, 2018, Fri.-Fri. On-line workshop: Many-Facet Rasch Measurement (E. Smith, Facets), www.statistics.com
Oct. 12 - Nov. 9, 2018, Fri.-Fri. On-line workshop: Practical Rasch Measurement - Core Topics (E. Smith, Winsteps), www.statistics.com