Fig. 2: Departures from the time trend separately for each year of the PISA assessment.
From: COVID-19, school closures, and student learning outcomes. New global evidence from PISA

The placebo test checks the robustness of results by estimating similar regression models for a time trend departure for every year before the pandemic. The figure shows estimates for each year with 95% confidence intervals. Only the departure in 2022 is substantial. This indicates that PISA mathematics results were stable before the pandemic and that the decline in 2022 was not accidental.