[bobthepanda]

Also, 1920 is a very arbitrary starting year. Why then?

In 1920 the Industrial Revolution has been going on for over 100 years, the US petroleum industry was already big enough to have been affected by antitrust action, and Henry Ford's assembly line has been enabling mass motorization for the better part of a decade.

[BoumTAC]

1920 is 100 years ago, so I don't think it's an arbitrary starting year. Also the older you start, the worst the data quality will be.