One important element of the current policy debate on what measures should be taken to reduce greenhouse gas emissions is the controversy over the costs of reducing those emissions. "Top-down" macroeconomic and general equilibrium models give much higher estimates of the costs than "bottom-up"...

In medical treatment and elsewhere, it has become standard to base treatment intensity (dosage) on evidence in randomized trials. Yet it has been rare to study how outcomes vary with dosage. In trials to obtain drug approval, the norm has been to specify some dose of a new drug and compare it...