Latest / Monetary Policy Explained with Fexingo: Central Banks, Money Supply, and Interest Rates / Why Central Banks Care About the Output Gap
Transcript
- Lucas: So the Federal Reserve looks at a lot of data every month — jobs numbers, inflation prints, consumer spending — but there's one number that quietly shapes everything else, and it's not even directly observable. Luna: You're talking about the output gap, right? That elusive measure of how far the economy is from its potential. Lucas: Exactly. The output gap is the difference between actual GDP and potential GDP — what the economy could produce if every worker and every machine were used at their most efficient, sustainable level. When actual GDP is below potential, you have a negative gap, meaning there's slack. When it's above, you have a positive gap, and that's when inflation pressures start to build. Luna: And central banks care because that gap is their compass for setting interest rates. Too much slack and you cut rates to stimulate. Too little slack and you're hiking. Lucas: Right. But here's the catch: potential GDP is not something you can measure directly. It's an estimate based on assumptions about labor force participation, productivity trends, and capital investment. And those estimates can be wildly wrong. Luna: Wildly wrong? Can you give me a concrete example? Lucas: Take the period right after the pandemic recession. In 2020 and 2021, many forecasters thought potential GDP had taken a permanent hit — that workers would drop out for good, that productivity would stall. So they saw a smaller negative gap and thought the economy would hit its ceiling much sooner than it did. Luna: And that misread led to what — keeping rates too high for too long? Or too low for too long? Lucas: Actually, it went both ways. In the early phase, they underestimated potential, so they saw less slack and kept rates higher than needed, which may have delayed the recovery. Then, as reopening happened faster than anyone expected, they realized the economy was running hotter than they'd thought — but by then, inflation was already spiking. Luna: It's like driving with a faulty fuel gauge. You think you have a quarter tank, but you're actually on empty. Lucas: Or worse — you think you're on empty when you've got half a tank, so you pull over unnecessarily. That's the real-time problem. The output gap is only clear in hindsight. The data you get in the moment is noisy and gets revised constantly. Luna: And because it's so uncertain, central banks have to make judgment calls. They can't wait for perfect data or they'd be reacting to a ghost. Lucas: That's where the art of central banking comes in. They use a mix of models, surveys, and labor market indicators to triangulate potential GDP. The Congressional Budget Office in the U.S. publishes its own estimate, and it's often cited as the official number, but even that comes with a wide margin of error. Luna: So when the Fed says 'we're approaching maximum employment,' they're really saying 'we think the output gap is closing.' Lucas: Precisely. And that's why the output gap feeds directly into the Phillips curve — the relationship between slack and inflation. If you think the gap is negative, you expect inflation to stay low. If you think it's positive, you expect prices to accelerate. Get the gap wrong, and your inflation forecast goes out the window. Luna: And we saw that happen in 2021 and 2022, when the Fed treated the inflation surge as 'transitory' partly because they believed there was still plenty of slack in the economy. Lucas: Right. And that's become one of the most studied policy mistakes in recent memory. The lesson wasn't just about supply chain shocks — it was about how easily the output gap can fool you. Luna: Before we go further — I've been thinking about how episodes like this are possible because of our listeners. A couple of dollars a month genuinely keeps these shows going. If you've gotten something out of walking through the economy with us, you can support us at buy me a coffee dot com slash fexingo. Lucas: Yeah, it really makes a difference. We keep everything ad-free, and that only works because of that kind of support. Anyway — back to the output gap. So if the gap is so hard to measure, why do central banks keep using it? Luna: Because it's still the best framework we have. It forces you to think about supply versus demand in a structured way. Lucas: Exactly. And it's not just about inflation. The output gap also matters for setting the neutral rate of interest — the rate that neither stimulates nor restricts the economy. If you think the gap is persistently negative, you might conclude that the neutral rate itself has fallen, which affects your entire policy path. Luna: So the output gap isn't just a diagnostic tool. It's embedded in how central banks project the future. Lucas: That's right. The Fed's dot plot, the ECB's projections — they all rely on an estimate of where the economy is relative to its potential. And when those estimates shift, the whole policy stance can shift with them. Luna: Let's talk about how they actually estimate it. I know there are different methods — statistical filters, production function approaches. Lucas: The most common is the production function approach. You estimate potential output as a function of potential labor, potential capital, and total factor productivity — that's the 'technology' component. Each of those inputs is smoothed out, often using statistical filters like the Hodrick-Prescott filter. Luna: But those filters have a well-known problem: they tend to see the recent past as the trend. So if you've just had a boom, they'll think potential is higher than it is, and vice versa. Lucas: That's the classic end-point problem, and it's a big reason why real-time estimates are so unreliable. The CBO's estimates for 2020, for instance, were revised down after the pandemic, but they were also constantly revised up as the recovery proved stronger than expected. Luna: It sounds like a lot of the debate is really about uncertainty, not just about the numbers. Lucas: Absolutely. And that's why central banks talk about 'risk management' rather than just point estimates. They don't just ask 'what's the output gap?' — they ask 'what if we're wrong?' That's why they sometimes act preemptively, like when they're worried about inflation overshooting, even if the data still shows slack. Luna: So for listeners who want to track the output gap themselves, what should they look at? Lucas: The simplest proxy is the unemployment rate relative to the natural rate, or NAIRU. When unemployment is below NAIRU, you're likely in positive gap territory. But that relationship has been unstable lately — we've had low unemployment and moderate inflation, so you also have to watch capacity utilization, job vacancies, and wage growth. Luna: And then there's the whole question of how much weight to put on the gap versus other indicators. Some economists argue that the Phillips curve is flat now, so the output gap doesn't matter as much for inflation. Lucas: That's a live debate. If the Phillips curve is flat, then running a hot economy doesn't automatically trigger inflation, and the output gap becomes less crucial for policy. But the experience of 2022 suggests it's not completely dead — it's just more nuanced, maybe nonlinear. Luna: So where does that leave us? Is the output gap still useful, or is it a relic of old-style macro? Lucas: I'd say it's still essential, but we need to hold it more lightly. Central banks are increasingly using a range of estimates and being explicit about the uncertainty. They're also paying more attention to supply-side shocks that can shift potential itself. Luna: Right — like the pandemic shifting labor supply, or AI boosting productivity. That's a whole new challenge for estimating potential. Lucas: Exactly. If AI genuinely raises productivity growth, potential GDP could be higher than current estimates. That would mean there's more slack than we think, which could allow the Fed to keep rates lower for longer without inflation. But it's too early to tell. Luna: And that's the thing — it's always too early. The output gap is a forward-looking concept, but we only have backward-looking data. Lucas: So the next time you hear a central banker say 'the economy is operating above potential' or 'we still have room to run,' remember that they're making a judgment call, not reading a dial. The output gap is a useful map, but it's drawn in pencil. Luna: And the eraser is always handy. Thanks for walking us through it, Lucas. Lucas: Thanks, Luna. And for our listeners, we'll keep digging into the numbers that move the world.