The perceived distance between social strata (different socio-economic, racial, or ethnic groups), usually measured by the amount of social contact between groups; see White et al. (2005) Sociol. Methods & Res. 34, 2. Agrawal et al. (2006) J. Econ. Geog. 6, 5, analysing knowledge flows, find that geographic proximity works to overcome social distance. Autant-Bernard et al. (2007) Papers Reg. Sci. 83, 3 define this term as the number of links between any two firms: ‘firms with a higher number of partners and a smaller social distance are more likely to be engaged together in a research project…in this context, social distance matters more than geographical distance.’