Multivariate analysis: an overview
http://www.eso.org/sci/software/esomidas//doc/user/98NOV/volb/node210.html
http://portal.unesco.org/ci/en/ev.php-URL_ID=2070&URL_DO=DO_TOPIC&URL_SECTION=201.html

Research Methods in Real Life 'Big data correlations making profit'
http://glinden.blogspot.de/2006/05/early-amazon-end.html
http://www.nytimes.com/2004/11/14/business/yourmoney/14wal.html
http://www.nytimes.com/2013/10/20/technology/to-catch-up-walmart-moves-to-amazon-turf.html