Hunting for keys to innovation: The diversity and mixing of occupations do not explain a city's patent and economic productivity

Cities are the main sources of innovation and hence of novel solutions to technological, social and biological issues, from climate change to growing populations. Statistically, the more people in a city, the more innovation in the city, as measured by patent production or by economic output (Bettencourt et al., PNAS 104(17) 2007). The conjectured mechanism for these increasing returns is that in more dense cities, people interact with more people|and more diverse people in terms of occupations and skills|and these interactions across boundaries leads to innovation and invention. Here we determine how diversity of occupations and their integration in US cities correlates with measures of innovation, measured by patents and gross metropolitan product (GMP). We nd that occupation diversity does not signicantly explain whether a city under- or over-innovates for a city of its size. A measure of occupational integration is proposed, but the correlation is also found to be weak with cities’ success. This suggests that more ne-scale data on interactions among people of dierent disciplines|or the culture, laws and peculiarities of cities|is required to better assess the under- or over-performance of innovation of cities.