Publishers Weekly has an article about how Vook did some research to determine optimal pricing for ebooks.
To develop those 10 rules, Vook examined what it calls the four successful factors for e-book pricing: categorization, discoverability, marketplaces, and the importance of libraries.
Testing different prices also reinforced the fact that pricing will vary title by title, Bateman stressed, and that in the digital world publishers need to check prices daily to see what impact it is having on the sale of e-books.
I liked rule 5, which does encourage a broad catalogue for writers marketing their ebooks:
Merchandising whole catalogues is more effective than single titles: "a rising tide lifts all boats."
I won't spoil the other results here. Click through to read the details: http://www.publishersweekly.com/pw/by-topic/digital/content-and-e-books/article/48188-rule-of-e-book-pricing-101.html