Some policy changes are hard to measure. Some are controversial to measure — you can measure them, but people will call you nasty names for doing so.

I expect that anyone who measured and forecast the health effects of reduction in lead pollution, back in the days of lead paint and leaded gasoline, was probably called "anti-business" or worse. Fortunately, they won anyway, and the effects are indeed measurable — in reduced cases of lead poisoning, and apparently in increased IQs of city residents.