The lower the index, the lower the level of concentration and the more diverse is the set of issuers. [4] In 2017, the index for non-financial corporations hit its lowest – most diverse – levels for some time (Graph 9). There was an uptick in concentration in 2018, but it is still at relatively low levels.
https://www.rba.gov.au/speeches/2019/sp-ag-2019-03-19.html  9/19  3/19/2019  Bonds and Benchmarks | Speeches | RBA  Graph 9  RMBS In 2018, non-banks issued the second largest amount of RMBS since the GFC, only narrowly eclipsed by 2017 issuance (Graph 10). This was associated with strong growth of non-bank housing loans, as they gained some market share from banks.