Preservation of legal materials that are not available online, particularly older editions of law books, etc., so as to make available the history of anything in regard to which all forms of in - depth analysis are dependent; (slaw.ca)
However, the backtesting period is limited by available histories for ETFs and for series used to estimate risk premiums. (cxoadvisory.com)
To investigate, we consider eight of the largest low volatility ETFs, all currently available, in order of longest to shortest available histories: (cxoadvisory.com)