Throughout our series on the follies of Module 4 of the Covid Inquiry, we have repeatedly encountered the use of counterfactual models (CM). These deserve a brief explanation, because much of the report’s most confident language rests upon them.
A counterfactual model asks a simple but unanswerable question: what would have happened if things had been different? For example: “Had we locked down one, two or three weeks earlier, we would have saved X number of lives.” Such claims sound authoritative. In reality, they are built not on observation, but on layers of assumption...
