How have search models influenced the current economic debates? John Quiggin had an interesting post up at Crooked Timber about how poorly the branch of economics that falls under search theory has done in the age of the internet. (Noah Smith has follow-up.)
Search and matching models are fascinating to me because they are central to both the debate over mass unemployment during the Great Recession as well as how economists understand the minimum wage. And here you can see search model being deployed for worse and for better.
The Great Recession
In his 2010 Annual Report, Federal Reserve Bank of Minnesota President Narayana Kocherlakota gave a presentation using the popular Diamond-Mortensen-Pissarides (DMP) search model to explain what he thought was wrong with the labor markets. Given that Kocherlakota was dissenting against QE2 at the time, a lot of eyes were on his arguments. Many focused on his infamous argument he later reversed that low rates cause disinflation, but I found this equally fascinating at the time.
The economy suffered from low job openings. But why were employers not creating job openings and hiring? Kocherlakota summarized the DMP model in this graphic:
Job openings and hires are a function of unemployment, productivity, and what was going on with the unemployed. He concluded that productivity after taxes was falling because of an increase in government debt, regulations and the proposed repeal of some of the Bush-era tax cuts. Also expansions of social insurance, including unemployment insurance and presumably the Medicaid expansion in Obamacare, was increasing the "utility" of not working. This, he believed, was the major reason why unemployment was so high and job openings so low. Using a back-of-the-envelope estimate with made-up numbers, he proposed that the natural rate of unemployment could be around 8.7 percent - very close to the then current 9.0 percent unemployment.
Think about this model and the recession long enough, and two things should jump out. The first is that this model, going back to Robert Shimer’s (2005) seminal work on the topic, is terrible at explaining movements in unemployment. The volatility in vacancies and productivity aren’t anywhere near the magnitude necessary to cause unemployment movements that we see in recessions. Productivity would need to drop significantly to create the changes in unemployment we see in recessions, and it doesn’t move to anywhere near that extent.
The second is that, as Robert Hall and many others have pointed out, productivity actually increased during the recent recession. It’s moving the wrong direction for it to impact unemployment the way we’d see it during the Great Recession. The unemployment-to-vacancy ratio also increased - 2009 was a fantastic time to create job openings according to this model, yet they collapsed. This is extra problematic given that economists have tried to respond to the initial problem by amplifying productivity movements in their models. But, out here in the actual world, the thing is simply moving in the wrong direction to make any sense.
Note that there’s no place for things like aggregate demand or the zero lower bound to plug into the equation. The only things that can matter are things like taxes, government uncertainty and social insurance, and they all work in the negative direction. That search models have become so influential to the background knowledge of unemployment helps explains the default ideology of why economists were so eager to find "structural" explanations for why unemployment was so high.
There’s some debate on this, but it looks like economists are softening on their opposition to raising the minimum wage, particularly if the question is phrased as whether or not a slightly higher minimum wage would pass a cost-benefit test. Search theory might be a reason why. If you are schooled in thinking of the labor markets in a search model, the idea that the minimum wage might not have an adverse employment effect makes more sense. A higher minimum wage means that low-wage workers will search harder for low-end jobs. They’ll be more likely to accept those jobs, and less likely to turn them over as well. These all would help raise the equlibrium employment level.
Even further, if you think that each job has a bit of a search friction surrounding it, then the idea that the employer has a little bit of monopoly power over the job makes sense. Employers might not raise wages to a market clearing rate because that, in turn, would mean having to raise the wages for all their workers. A minimum wage pushes against that. Understanding the labor markets through this lens ideas helps explain why any disemployment effects are minimial compared to the economics 101 story.
As I read it, much of this theory took hold in labor economics to help explain the data people were seeing. Why were there so many vacancies in fast food? Why didn't minimum wage hikes obviously cause unemployment in the data? This should tell us something - theory, when built up out of observations and data, can tell us something useful. But the same theory moved over to the business cycle, where it ignores conflicting data and is propelled downward by partisan and ideological forces, can be an utter disaster.