Recent literature suggests two mechanisms through which the start-up of new firms contributes to economic development: the growth of start-ups and competition among incumbent firms induced by the start-ups. While existing studies derive the competition effect indirectly, this paper deploys a direct measure, called market mobility, to approximate the induced competition effect. The empirical results are consistent with the idea that both effects are important in explaining the long-term economic impact of start-ups. First, the most successful start-ups grow to become high-growth firms, and second, the entry of new firms stimulates incumbent firms to perform better. [ABSTRACT FROM AUTHOR]