Working Paper: CEPR ID: DP16147
Authors: Ben Vollaard; Jan C. van Ours
Abstract: Hard evidence on bias in expert reviews and its consequences for ratings is rare. This holds particularly true for conflicts of interest that are thought to be common in non-blind product reviews but are not readily observable: ad hoc relationships between reviewers and producers. We present a textbook case of a long-running expert product review in the food service industry for which we happen to know the reviewer's conflict of interest: being affiliated to one particular producer. As is typical, only insiders were aware of the possible source of bias in the review. The review resembles other non-blind tests of product quality. We obtained detailed data to map the consequences of the conflict of interest. We find evidence of a sizable bias in the reviewers' ratings. Our findings suggest that reviewers' ad hoc relationships with producers, often dismissed as `coming with the job', can be very harmful.
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Edges that are evidenced by causal inference methods are in orange, and the rest are in light blue.
| Cause | Effect |
|---|---|
| conflict of interest (G34) | higher ratings for fishmongers (Q22) |
| supplier association (L14) | higher ratings for fishmongers (Q22) |
| product attributes (L68) | ratings for fishmongers (Q22) |
| ratings for businesses stocked by supplier (L81) | exceed ratings explained by product attributes (L15) |