The survey in 2017 had a 56% response rate. The 2023 survey had a 27% response rate.

Comparing those 2 datasets is meaningless. It’s just an exercise in how good the researchers are at guessing when trying to control for selection bias.

There were also significant changes in the test and how the test was administered (from computer or paper to only tablets).

Also if you look at the results some of them are too large to be readable. A 50% increase in people operating at or below level 1 (40% if you exclude non-native born). That would have to mean a drastic drop in 2017 such that something like 75% of kids graduating high school are doing so at or below level 1.

Also level 3 has no direct grade equivalence. If it did it would probably be around 9th grade not 6th.