Fig. 1

Community Assignments: Data and Null Model. The left hand plot shows community assignments for the 30 industry portfolios over the 88 years from 1927 to 2014. This structure is constant prior to 1960, but shows substantial changes in the latter half of the sample. The right hand plot shows a representative run of the “null model”. The null model is constructed by randomizing the order of the 88 sample years, and is constant over the entire sample