Grades and statistics

by danjo

From Johan Norberg we learn that

A couple of days ago, Swedish private schools were strongly criticised for giving their students better grades. Unfair, said the critics. After having looked at the results from standardised tests, Skolverket – the Swedish National Agency for Education – explains why: Students in private schools simply perform better.

But by following the link to the article in SvD, we learn that the reason Skolverkets study showed one thing and the earlier study by Cristina Wikström showed another is that Skolverket apparently disregarded the selection bias inherent in private schools cherry picking high performing students. I’m not convinced, Johan.