Let’s talk about you and me (and our respective defining group memberships), let’s talk about all the good things (obtaining accurate scores) and the bad things (model misspecification) that may be. Let’s talk about DIF. Differential item functioning (DIF) is the psychometric jargon term for when items perform differently depending on characteristics of the person answering the item. Analyses for detecting DIF should be part of any initial calibration study of a COA, PRO, or test and are readily available … Read More

Last time, we had a riveting discussion about reliability and mentioned that validity is also something to consider when talking about tests/assessments/scales and the scores that come from them. So let’s do that. Previously, we used Score = truth + error to talk about measurement and the idea of reliability. That is, the more garbage (error) there is in your scores, the less reliable they will be. If your scores are full are noise, then your boat is already sunk. … Read More