The Broken Thermostat Model
Some systems never self-correct because the feedback mechanism is in the wrong place.
The Broken Thermostat Model is a metaphor-turned-framework that Stevenson derives from a story told by his boss Caleb Zucman. Caleb described how his house had a thermostat placed too close to the fireplace. When the fire was lit in winter, the thermostat would immediately register warmth and shut off the heating upstairs, leaving the rest of the house freezing. No matter how many times they moved the thermostat, the feedback mechanism kept measuring the wrong thing.
Stevenson applies this metaphor to the global economy. Economists and policymakers assume the economy works like a well-placed thermostat: if it gets too cold (recession), you turn up the heat (lower rates, stimulus), and the system self-corrects. But when the thermostat is broken, the measurement of temperature is disconnected from the actual condition of the system. The heat (monetary stimulus) warms the area around the thermostat (financial markets, asset prices) while the rest of the house (ordinary people's living standards) stays freezing.
The framework is a diagnostic tool for any system that appears to have self-correcting mechanisms but persistently fails to correct. The solution is never to turn up the heat further but to find and fix the broken feedback mechanism.
- A system with a broken feedback mechanism will never self-correct no matter how strong the input.
- Measuring the wrong variable gives a false sense of progress while the real problem persists.
- The solution to a broken thermostat is not more heat but a better-placed sensor.
- People close to the fire will always report warmth, making them unreliable diagnosticians of the system's true temperature.
- Persistent failure of predictions should trigger investigation of the feedback mechanism, not more confident predictions.
- Identify the Persistent FailureLook for systems where corrective action is taken repeatedly but the problem persists or worsens. In the economy, this was a decade of stimulus that failed to produce sustained recovery. In organizations, it might be repeated restructurings that fail to improve performance.Pro tipThe clearest signal of a broken thermostat is when experts keep predicting improvement that never materializes. Repeated prediction failure in the same direction is diagnostic.
- Map What Is Being Measured vs. What MattersIdentify the metrics the system uses as feedback (the thermostat) and compare them to the actual outcome that matters (the temperature in the rooms people live in). Are they measuring GDP growth while ignoring median wage stagnation? Are they measuring stock price while ignoring employee satisfaction?WarningThe people responsible for the metrics often have incentives to maintain the current measurement system because it makes them look good.
- Trace Why the Measurement Is DisconnectedUnderstand the mechanism by which the corrective action warms the sensor without warming the system. In the economy, monetary stimulus inflates asset prices (which are easily measured) without reaching consumer spending (which is harder to measure and slower to respond).Pro tipFollow the money or the mechanism of transmission. If the corrective action goes through intermediaries, each intermediary is a potential point of disconnection.
- Propose Measurement Reform, Not More HeatThe solution is not to increase the corrective input but to fix the feedback mechanism. In economic terms, this means measuring living standards rather than GDP, or directing stimulus to consumers rather than through financial markets. In organizations, it means measuring the outcomes that matter rather than the inputs that are easy to track.Pro tipExpect resistance to measurement reform from those who benefit from the current broken measurement. People near the fire are comfortable and will defend the thermostat's placement.WarningChanging measurement systems is politically harder than increasing inputs, which is exactly why broken thermostats persist.
After 2008, central banks pumped trillions into the financial system through quantitative easing. Financial markets recovered rapidly, stock indices reached new highs, and property prices inflated. Yet median wages stagnated, living standards declined, and millions of families fell into poverty. The financial market thermostat registered warmth while the broader economic house remained freezing.
Caleb and his wife repeatedly called engineers to reposition the thermostat in their Tokyo home. Each time it was moved, the problem seemed to improve temporarily before recurring. The fundamental issue was not the thermostat's location but the system's design, which placed the measurement point in a zone that was unrepresentative of the whole house.
Caleb Zucman, Stevenson's boss and mentor at Citibank, told the thermostat story during a dinner in Tokyo. Caleb had a beautiful house in the Yoyogi area of Tokyo where the heating system had a persistent flaw: the thermostat was installed too close to the fireplace. When they lit a fire in winter, the thermostat would immediately sense warmth and shut off the central heating, leaving the upstairs rooms cold. No matter where they repositioned the thermostat, the problem kept recurring.
Stevenson recognized this as the perfect metaphor for the post-2008 global economy. Central bank stimulus was the fire; financial markets were the thermostat; and ordinary households were the freezing upstairs rooms. The more aggressively central banks stimulated, the more financial markets warmed up, triggering the false signal that the economy was recovering, while the actual economy remained cold.