Requirement for research resources and risk of academic career choice.

, time to reach career independence. , reciprocal of the salary premium of non-academic careers. , ratio of Ph.D. graduates pursuing an academic position. The data of research expenditures are obtained from http://www.nsf.gov/statistics/nsf11313/. The salary data are obtained from http://www.nsf.gov/statistics/nsf09317/. We use the salary data of zoology instead of ecology because we could not obtain data for ecology. The data of career choice of Ph.D. graduates are obtained from http://www.nsf.gov/statistics/nsf03310/.