Entries by Nathan Thompson, PhD

What is the generalized credit model (GPCM)?

The generalized partial credit model (GPCM, Muraki 1992) is a category in a group of families in item response theory (IRT). It is designed to work with items that are partial credit.  That is, instead of just right/wrong as possible, scoring an examinee can receive partial points for completing some aspects of the item correctly.  For […]

What is scaled scoring on a test?

Scaled scoring is a process used in assessment and psychometrics to transform exam scores to another scale (set of numbers), typically to make the scores more easily interpretable but also to hide sensitive information like raw scores and differences in form difficulty (equating).  For example, the ACT test produces scores on a 0 to 36 […]

R for psychometrics

If you are dealing with data science, which psychometrics most definitely is, you’ve probably come across  R. It is an environment that allows you to implement packages for many different types of analysis, which are built by a massive community of data scientists around the world. R has become one of the two main languages […]

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Flag exam cheating 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) […]

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Subject Matter Experts (SME) in Exam Development

Subject matter experts are an important part of the process in developing a defensible exam.  There are several ways that their input is required.  Here is a list from highest involvement/responsibility to lowest: Serving on the Certification Committee (if relevant) to decide important things like eligibility pathways Serving on panels for psychometric steps like Job […]

MICROCAT: What was assessment like in the 1980s?

ASC has been empowering organizations to develop better assessments since 1979.  Curious as to how things were back then?  Below is a copy of our newsletter from 1988, long before the days of sharing news via email and social media!  Our platform at the time was named MICROCAT.  This later became modernized to FastTest PC […]

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 (IRT 2PL). Consider the following 3PL equation (simplified from Hambleton & Swaminathan, 1985, Eq. 3.3).  The IRT […]