Shawn Achor (2011). “The Happiness Advantage: The Seven Principles of Positive Psychology that Fuel Success and Performance at Work”, p.11, Random House
Philippe Halsman (1981). “The Mask Falls: Psychological Portraits by Philippe Halsman : a Retrospective Collection of Images from the Photographer's Studio, to be Sold by Public Auction, Friday, November 13, 1981, at 7:00 P.m. at Harris Auction Galleries”