Formal Employment is a Consequence of Skill Diversity in Cities

Why do cities with larger populations in developing countries create relatively more formal employment? We build a model where skill diversity increases with working age population size, and urban agglomeration economies result from complementarities at the firm level between workers with diverse skills. Inactive, unemployed,or self-employed (informal) workers are gradually absorbed by firms as new sectors appear via an evolutionary process ofskill recombination by firms.The model makes four predictions: (1) faster firm entry in less complex sectors, (2) higher wages in more complex sectors, (3) relatively more formal employment in larger cities, and (4) faster formal employment growth in cities that have more of the skills needed in more complex sectors. Since skills are not observable, sector complexity is computed from sector diversity and ubiquity, and skill availability from inter-industry labor transitions. We find strong empirical support for all of the predictions when tested with social security data for Colombia for the period 2008-2015.