The fraction of self-employed rises in recessions because wage work is more sensitive than self-employment to the business cycle, not because of necessity entrepreneurship. Graduating during a recession reduces the probability of starting a business for the next 11 years.

We propose a strategy to identify the complementarity or substitutability among technology bundles. Differences between the observed distribution of technology choices can be subjected to statistical tests. Combinations of technologies that occur with greater frequency than would occur under...