Investigation of item parameter drift of anchor items in TIMSS practices

This study examines item parameter drift (IPD) in eighth-grade science anchor items from the paper-based cycles of the Trends in International Mathematics and Science Study (TIMSS) in 2011, 2015, and 2019. Korea, Italy, and Saudi Arabia were selected as examples of high-, medium-, and low-achieving education systems to explore how IPD develops across different performance contexts. Using the three-parameter logistic model (3PLM) estimated in Lexter and D² statistics computed in R, the study evaluated changes in item parameters across years and country pairs for 30 multiple-choice anchor items. The results showed that eight items exhibited temporal IPD in at least one comparison period, with most drift concentrated in the 2015–2019 and 2011–2019 contrasts. Drift occurred mainly in chemistry items at the applying cognitive level, alongside a smaller number of biology and physics items. Cross-country analyses identified 18 items with IPD in at least one country pair, with the largest number of drifting items observed between Korea and Saudi Arabia. Items involving symbolic chemical notation and representational demands were especially likely to drift across systems that differ in achievement level and opportunity to learn. These findings indicate that IPD in TIMSS science is concentrated in a subset of anchor items and is shaped jointly by temporal change and cross-national differences. The study underscores the importance of routine IPD monitoring, targeted review of repeatedly drifting items, and careful anchor selection to support valid cross-cycle and cross-national comparisons in large-scale assessments.