The most prominent theory in macroeconomics is New Keynesianism. One of the most striking and unique predictions that New Keynesianism makes is that when the economy is in a recession, everything gets flipped upside down. Specifically, when interest rates are at the zero lower bound and the economy is stuck in a liquidity trap, most of the things that would usually improve economic outcomes actually worsen them.
The NK model predicts that supply-side loosenings, like lifting employment regulations, cutting taxes or liberalising immigration laws, will actually make things worse in a recession, as will interventions that increase price flexibility. However, this prediction—familiar from Paul Krugman's NYT columns since 2007—seems to have been strongly challenged in a batch of recent papers.
The first is "Supply-Side Policies in the Depression: Evidence from France", by Jérémie Cohen-Setton, Joshua K. Hausman, and Johannes F. Wieland. It, as the title suggests, looks at data in from the great depression in France, one of the areas that suffered it from the longest, due to the obsessive desire of the Bank of France never to sever the currency's link with gold. The Keynesian model would predict that devaluation and leaving gold were the only game in town, but in fact the negative supply-side shocks that happened at the same time depressed activity, even in a deep slump.
The effects of supply-side policies in depressed economies are controversial. We shed light on this debate using evidence from France in the 1930s. In 1936, France departed from the gold standard and implemented mandatory wage increases and hours restrictions. Deflation ended but output stagnated. We present time-series and cross-sectional evidence that these supply-side policies, in particular the 40-hour law, contributed to French stagflation. These results are inconsistent both with the standard one-sector new Keynesian model and with a medium scale, multi-sector model calibrated to match our cross-sectional estimates. We conclude that the new Keynesian model is a poor guide to the effects of supply-side shocks in depressed economies.
The second is "Are Supply Shocks Contractionary at the ZLB? Evidence from Utilization-Adjusted TFP Data", by Julio Garín, Robert Lester, and Eric Sims. It looks at more extensive data on productivity. The Keynesian model predicts worse productivity improvements from supply shocks that occur in slumps but the data finds quite the opposite result.
The basic New Keynesian model predicts that positive supply shocks are less expansionary at the zero lower bound (ZLB) compared to periods of active monetary policy. We test this prediction empirically using Fernald's (2014) utilization-adjusted total factor productivity series, which we take as a measure of exogenous productivity. In contrast to the predictions of the model, positive productivity shocks are estimated to be more expansionary at the ZLB compared to normal times. However, in line with the predictions of the basic model, positive productivity shocks have a stronger negative effect on inflation at the ZLB.
The third, "What Was Bad for General Motors Was Bad for America: The Automobile Industry and the 1937/38 Recession" by Joshua K. Hausman, tackles the question less directly, finding that shocks that impacted the car industry, even if they weren't aggregate, demand-side shocks, nevertheless had large impacts on overall output and income.
I think the New Keynesian model is wrong about a lot of things. It seems that the impact of supply-side moves in a recession is yet another prediction it gets wrong.