Pitfalls of amateur regression: The Dutch New Herring controversies

We analyse data from the final two years of a long-running and influential annual Dutch survey of the quality of Dutch New Herring served in large samples of consumer outlets. The data was compiled and analysed by a university econometrician, whose findings were publicized in national and international media. This led to the cessation of the survey amid allegations of bias due to a conflict of interest on the part of the leader of the herring tasting team. The survey organizers responded with accusations of failure of scientific integrity. The econometrician was acquitted of wrong-doing by the Dutch authority, whose inquiry nonetheless concluded that further research was needed. We reconstitute the data and uncover its important features which throw new light on the econometrician's findings, focussing on the issue of correlation versus causality: the sample is definitely not a random sample. Taking account both of newly discovered data features and of the sampling mechanism, we conclude that there is no evidence of biased evaluation, despite the econometrician's renewed insistence on his claims.