Economist's View has a remarkable thread off a study summarizing the multiplier effect on GDP from infrastructure spending. The paper concludes that the multiplier is one, but the thread makes it clear (a) that plenty of smart, well-informed people do not agree; and (b) that macro, taken as a whole, remains disturbingly close to phrenology.
Recall: phrenology--the "science" of studying head-bumps--was not exactly wrong; there is indeed a geography of the brain, and we can learn important stuff by tracking what happens where. But in its long infancy, the name "phrenology" was pretty much a synonym for "charlatanism' (the correlation is one?). I wouldn't go so far as to say that macro is charlatanism, although god knows there is plenty of charlatanism on the fringes of macro. And the Thoma thread makes it pretty clear that for all the effort and energy, we've made embarrassingly little progress towards reaching a consensus on what works and what does not ("reasonable minds may differ"="local mileage may vary"="whirl is king, Zeus being dead").
Meanwhile people who ought to know better have a new mantra.