Professor Alex Edmans from the London Business School argues in the book "May Contain Lies" that much of the information we consume through statistics, reports, and studies deserves a warning similar to those appearing on cigarette packs. The author proposes an inference ladder where a claim is not a fact, a fact is not data, data is not evidence, and evidence is not proof. Climbing each rung requires scrutiny, as the number on an Excel spreadsheet may be mathematically correct and yet say very little about reality.
The article warns about the inversion of the scientific method in public policy: instead of evidence-based policies, policy-based evidence is produced—that is, the answer is chosen first and then the numbers that justify it are sought. Beja Airport is presented as a paradigmatic example of this practice, where dozens of feasibility studies and optimistic projections justified a project that reality has proven wrong.
The author then focuses on Portuguese municipal taxes, arguing that the economic-financial justification required by law is frequently just a bureaucratic ceremony. The concrete example cited is the idea of Porto's mayor to increase the tourist tax to fund free public transport, since the tourists who pay the increase do not benefit from the fare-free status of those same transport services.
When facing any study, Edmans suggests three essential questions: who chose the assumptions, what result would we obtain with equally plausible but less convenient assumptions, and would the conclusion survive if it contradicted the interest of whoever commissioned the work. The author argues that a good justification should include sensitivity analysis and not just produce a precise number with two decimal places.
