Entries by Nathan Thompson, PhD


Assessment Systems presents at the Conference on Test Security (COTS)

The Conference on Test Security is a scholarly conference devoted to the topic of security in educational, credentialing, and employment assessment.   Test fraud/cheating is one of the most salient threats to score validity, and can invalidate the entire exam, defeating the important goals such as ensuring that only qualified people are allowed to practice a […]

Four-Fifths Rule: Fair Employment Selection

The Four-Fifths Rule is a term that refers to a guideline for fairness in hiring practices in the USA.  Because tests are often used in making hiring decisions, the Four-Fifths Rule applies to them so it is an important aspect of assessment in the workforce, but it also applies to other selection methods, such as […]


Classical Test Theory: Item Statistics

Classical Test Theory (CTT) is a psychometric approach to analyzing, improving, scoring, and validating assessments.  It is based on relatively simple concepts, such as averages, proportions, and correlations.  One of the most frequently used aspects is item statistics, which provide insight into how an individual test question is performing.  Is it too easy, too hard, too […]

Content Validity in Assessment

Content validity is an aspect of validity, a term that psychometricians use to refer to evidence that interpretations of test scores are supported.  For example, predictive validity provides evidence that a pre-employment test will predict job performance, tenure, and other important criteria.  Content validity, on the other hand, focuses on evidence that the content of […]

Predictive Validity of Test Scores

Predictive Validity is a type of test score validity which evaluates how well a test predicts something in the future, usually with a goal of making more effective decisions about people.  For instance, it is often used in the world of pre-employment testing, where we want a test to predict things like job performance or […]


Classical Test Theory vs. Item Response Theory

Classical Test Theory and Item Response Theory (CTT & IRT) are the two primary psychometric paradigms.  That is, they are mathematical approaches to how tests are analyzed and scored.  They differ quite substantially in substance and complexity, even though they both nominally do the same thing, which is statistically analyze test data to ensure reliability […]

All Psychometric Models Are Wrong

The British statistician George Box is credited with the quote, “All models are wrong but some are useful.”  As psychometricians, it is important that we never forget this perspective.  We cannot be so haughty as to think that our psychometric models actually represent the true underlying phenomena and any data that does not fit nicely […]

Credential or Certification Management System

A Certification Management System (CMS) or Credential Management System (CMS) plays a pivotal role in streamlining the key processes surrounding the certification or credentialing of people, namely that they have certain knowledge or skills in a profession.  It helps with ensuring compliance, reducing business operation costs, and maximizing the value of certifications. In this article, […]