Background: Examinees may not make enough effort when responding to test items if the assessment has no consequence for them. These disengaged responses can be problematic in low-stakes, large-scale assessments because they can bias item parameter estimates. However, the amount of bias, and whether this bias is similar across administrations, is unknown. This study compares the degree of disengagement (i.e., fast and non-effortful responses) and the impact of disengagement on item parameter estimates in the Programme for International Student Assessment (PISA) across the 2015 and 2018 administrations.

Method: We detected disengaged responses at the item level based on response times and response behaviors. We used data from the United States and analyzed 51 computer-based mathematics items administered in both PISA 2015 and PISA 2018. We compared the percentage of disengaged responses and the average scores of the disengaged responses for the 51 common items. We filtered disengaged responses at the response- and examinee-levels and compared item difficulty (P+ and b) and item discrimination (a) before and after filtering.

Results: Our findings suggested that there were only slight differences in the amount of disengagement in the U.S. results for PISA 2015 and PISA 2018. In both years, the amount of disengagement was less than 5.2%, and the average scores of disengaged responses were lower than the average scores of engaged responses. We did not find any serious impact of disengagement on item parameter estimates when we applied response-level filtering; however, we found some bias, particularly on item difficulty, when we applied examinee-level filtering.

Conclusions: This study highlights differences in the amount of disengagement in PISA 2015 and PISA 2018 as well as the implications of the decisions made for handling disengaged responses on item difficulty and discrimination. The results of this study provide important information for reporting trends across years.