"As [economist Robert] Gordon acknowledges many times, we don't have a good tool for measuring the impact of innovation on people's lives. Like other economists, Gordon uses something called Total Factor Productivity (TFP), which is meant to capture efficiency due to innovation. TFP is based on GDP but takes into account the hours we work and the equipment we use.
"The truth is, while economic measurements like TFP can be useful for understanding the impact of a tractor or a refrigerator, they are much less useful for understanding the impact of Wikipedia or Airbnb.
"How do you calculate the value of millions of pages of free information at your fingertips? How do you calculate the impact of the entire hospitality industry flipped on its head? In the future, GDP may not grow as fast as it did in the past--or, for all we know, it may--but that alone doesn't tell...