Need to find credible research on the positive impact sending a regular newsletter has on a company's customer retention, referrals and ultimately, profitability. Please type the phrase "get the news" at the top of your coverletter.
By credible, I mean from a nationally (or internationally) recognized source - Forbes magazine, Inc. Harvard, Wharton, etc. not just a blog from some random guy.
I'm looking for statistical data that shows increases in revenue in various industries, also comparatives... Company X sends newsletters, company Y doesn't...company X retains more customers, and makes more money, etc.
Would also like something that shows customer retention/profitability for one company before using a newsletter and after.
Note: I don't really need an article written...mainly just the information I asked for compiled into a document with links to the source.