Nationality French
Year of selection2015
InstitutionTilburg University
RiskSocio-economic risks

Type of support

Post-Doctoral Fellowship

Granted amount

120 000 €


2 years

When a new product—a drug or a pesticide, say—is deemed safe and released on the market, someone has decided to give it their seal of approval. More likely, a group of people have come together, evaluated the risks involved, and made a collective decision. This makes Dr. Thomas Boyer-Kassem wonder how they went about it, if they pooled their risk assessments in the best way, and if there even is a “right” way! Originally trained in physics, today he is applying mathematical tools to philosophical questions to understand the best ways for groups to make collective judgments. His theoretical work aims to answer questions that are relevant to expert committees, corporate boards, political bodies—any group of individuals charged with making decisions together about risks.

“Aggregating judgments is no simple matter,” says Dr. Boyer-Kassem, and no one has yet addressed how risk assessments, specifically, should be handled. His work will identify whether they are different from other judgments and require specific rules or methods to be aggregated. To illustrate the point, he imagines a committee debating whether to authorize a new pesticide, given the guideline that the health risk must be lower than 5%. If four experts evaluate the risk at 4% and another at 14%, how should their assessments be combined? Should it be a four-against-one decision and, so, the product is approved? Or is it more appropriate to calculate the average of their votes (6%) and, thus, reject the pesticide? “Two plausible procedures to collectively assess a risk and decide on its acceptability lead to two different outcomes,” Dr. Boyer-Kassem observes. It only gets more complex if the threshold of acceptability (the 5%, in this case) is not pre-determined. Each person will have his or her own definition of “acceptable risks” to the table. This begs the question, then, of when to aggregate their positions: before they’ve each applied their acceptability limit and drawn a conclusion? Or is it better for each to come to a conclusion before aggregation, leaving out their individual thresholds? Or maybe something in between…?

Answering these questions about which decision procedures produce the optimal collective conclusion is one goal of the project. But, of course, there is unlikely to be a one-size-fits-all solution. The best method of aggregating risk assessments will depend on various factors regarding the problem at hand (the threshold agreed upon, the diversity of individuals’ views) and the purpose assigned (to be more or less cautious, represent the diversity of opinions or the middle of the road). “My objective,” Dr. Boyer-Kassem explains, “is to develop a sort of map, distinguishing among a dozen types of aggregation problems and identifying the best method to arrive at a collective decision in each scenario.”
Dr. Boyer-Kassem will develop these conclusions by investigating existing logical and mathematical models of judgment aggregation that might be applicable to the risk aggregation problem, modifying them as necessary and potentially developing new ones. By mapping out the landscape of risk assessment in group decisions his results should be easily applicable to a variety of collectives. These might be expert panels, research groups, citizens’ associations… – any group of people in need of rational methods to arrive, together, at the best evaluation of the risks before them and the optimal decision that follows.

Scientific title: Collective Decisions: How To Aggregate Risk Assessment and Risk Acceptability

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