Entries by Nathan Thompson, PhD

Flagging invalid scores with Time-Score analysis

Psychometric forensics is a surprisingly deep and complex field.  Many of the indices are incredibly sophisticated, but a good high-level and simple analysis to start with is overall time vs. scores, which I call Time-Score Analysis.  This approach uses simple flagging on two easily interpretable metrics (total test time in minutes and number correct raw score) […]

ASC expertise recognized in Education Week

ASC’s expertise in computerized adaptive testing (CAT) is recognized around the world.  Back in 2008, our co-founder was asked to contribute to an Education Week article about the topic.  CAT was seeing a significant growth in the US K-12 market at the time, so it was a timely piece.  Here’s part of the article: In […]

What is the two parameter IRT model (2PL)?

Item response theory is the predominant psychometric paradigm for mid or large scale assessment.  As noted in my introductory blog post, it is actually a family of models.  In this post, we discuss the two parameter IRT model (2PL). The 2PL is described by the following equation (simplified from Hambleton & Swaminathan, 1985, Eq. 3.3): […]

What is the three parameter IRT model (3PL)?

Item response theory (IRT) is an extremely powerful psychometric paradigm that addresses many of the inadequacies of classical test theory (CTT).  If you are new to the topic, there is a broad intro here, where you will learn that IRT is actually a family of mathematical models rather than one specific one.  Today, I’m talking […]

What is the classical item facility statistic in psychometrics?

Classical test theory is a century-old paradigm for psychometrics – using quantitative and scientifically-based processes to develop and analyze assessments to maximize their quality.  (nobody likes unfair tests!)  The most basic and frequently used item statistic from classical test theory is the P-value.  It is usually called item difficulty but is sometimes called item facility, […]

How can you implement an Angoff cutscore on a test scored with item response theory?

The modified-Angoff method is arguably the most common method of setting a cutscore on a test.  The Angoff cutscore is legally defensible and meets international standards such as AERA/APA/NCME, ISO 17024, and NCCA.  It also has the benefit that it does not require the test to be administered to a sample of candidates first; methods like […]

What is linear on the fly testing?

Linear on the fly testing (LOFT) is an approach to delivering assessments to examinees.  In general, there are two families of test delivery.  Static approaches deliver the same test form or forms to everyone; this is the ubiquitous and traditional “linear” method of testing.  Algorithmic approaches deliver the test to each examinee based on a […]