Why does a haircut or a college class cost so much more today than it did 50 years ago? The service itself hasn't fundamentally changed. A haircut still takes about the same amount of time and effort. A professor can only teach so many students at once. Yet, prices in these areas seem to constantly outpace inflation.

This isn't just a feeling; it's a well-documented economic phenomenon. The answer lies in how different parts of the economy grow at different speeds. In the 1960s, economists William Baumol and William Bowen were studying the finances of performing arts organizations and noticed this exact problem. They saw that a string quartet in 1966 required the same four musicians playing for the same amount of time as a quartet in 1866. There was no way to make them more 'productive' without changing the nature of the music. This observation led to a broader theory about costs in the service sector.

To understand the Baumol effect, it helps to think of the economy as having two main sectors. Let's call them the 'progressive' sector and the 'stagnant' sector.

The progressive sector includes industries like manufacturing, telecommunications, and software development. Here, innovation and technology lead to huge gains in productivity. A single factory worker today can produce far more cars than they could 50 years ago, thanks to robotics and automation. A software engineer can write code that serves millions of people. Because each worker produces more value, their wages can rise without increasing the cost of the final product. In fact, prices for things like televisions and computers have often dropped over time.

The stagnant sector includes jobs that are heavily reliant on human interaction and can't easily be automated. Think of nurses, teachers, musicians, and barbers. A nurse can only care for a certain number of patients at a time. A teacher's effectiveness depends on personal attention. Productivity in these fields is relatively stable.

So, what connects these two sectors? Labor. People can choose to work in either sector. If the car factory starts paying higher wages because its workers are more productive, what happens to the local hospital or school? To attract and retain qualified nurses and teachers, they have to raise their wages to remain competitive. If they don't, their employees will leave for better-paying jobs in the progressive sector.

This creates a dilemma. The hospital's costs go up because they're paying higher salaries, but their productivity hasn't changed. A nurse isn't caring for twice as many patients to justify the pay raise. The result is that the cost of healthcare goes up.

Let's imagine a simple economy with only two industries: making widgets and giving haircuts. Suppose a technological breakthrough allows widget-makers to double their output. Their company makes more money, and they get a 50% raise.

Now, the barbers in town see the widget-makers' salaries go up. To keep their barbers from quitting to go work at the widget factory, the barbershop owner has to give them a 50% raise, too. But the barbers are still giving the same number of haircuts per day. To cover the higher labor costs, the owner must increase the price of a haircut. The cost of the service rises, not because the barbers are less efficient, but because wages across the whole economy have gone up.

This is often called a 'cost disease' because it seems to be an unavoidable consequence of technological progress in other parts of the economy. The very innovation that makes some goods cheaper is what drives up the cost of labor-intensive services.