From Lipperusfundflows.com (pdf): 

      "The Lipper FMI Fund Flows database consists of the assets of all open-end mutual funds in the United States mutual fund industry distributed on a weekly basis since January, 1992. Asset and price changes in each fund share class are calculated to differentiate the asset change due to net investor flows from the asset change due to market performance. Reports on the fund flow component have been maintained and added to a dataset now consisting of 18,400 share classes managing assets of $9.4 Trillion. The funds can be aggregated by sector, investment style, fund complex, or drilled-down and flows reported for individual or combined fund share classes. Funds report information in weekly and monthly frequencies. Weekly reported information is distributed in 12-week aggregate reports and rankings by sector. These 12-week reports provide the basis for Lipper FMI’s legacy business. Many Lipper FMI customers have upgraded their subscription to all historical information (780 weeks; 15 years) in all sectors.
    Weekly and monthly reported flows are aggregated to calculate and report a moving average, which describes the weekly ‘Flow Rate ’. This enables a calculation of the rate of flow for an entire fund dataset, reporting both weekly and monthly. "