«One reason for relatively low productivity growth in the nontradables sector is its substancial overlap with services, which are inherently less susceptible to standardization and mechanization than are manufactures or agriculture. This is not to say that there cannot be substantial technical advance in services. To use an example from Baumol and Bowen (1966), the hourly output of a string quartet has changed dramatically since Haydn’s day. Through modern audiovisual and communications strategy, the music that once entertained at most a roomful of listeners (hence the name “chamber music”) now can be brought instantly to millions worldwide.»

Foundations of International Economics, M. Obstfeld e K. Rogoff