[FDG]

This paper could be relevant:

http://ftp.iza.org/dp3648.pdf

quoting the abstract:

How valuable are cognitive and social abilities for entrepreneurs’ incomes as compared to
employees? We answer three questions: (1) To what extent does a composite measure of
ability affect an entrepreneur's earnings relative to employees? (2) Do different cognitive
abilities (e.g. math ability, language ability) and social ability affect earnings of entrepreneurs
and employees differently?, and (3) Does the balance in these measured ability levels affect
an individual's earnings? Our individual fixed-effects estimates of the differential returns to
ability for spells in entrepreneurship versus wage employment account for selectivity into
entrepreneurial positions as determined by fixed individual characteristics. General ability has
a stronger impact on entrepreneurial incomes than on wages. Entrepreneurs and employees
benefit from different sets of specific abilities: Language and clerical abilities have a stronger
impact on wages, whereas mathematical, social and technical ability affect entrepreneurial
incomes more strongly. The balance in the various kinds of ability also generates a higher
income, but only for entrepreneurs: This finding supports Lazear's Jack-of-all-Trades theory.