Documentation Usability: A Few Things I’ve Learned from Watching Users
http://www.idratherbewriting.com/2009/04/28/documentation-usability-a-few-things-i%E2%80%99ve-learned-from-watching-users/

Johnson, Tom H.
I'd Rather Be Writing
2009

Abstract:

Even though your customers may not read manuals, your tech support team probably does, which means someone is reading the manuals and using them to help others. But if your users find it easier to call someone, wait on hold for an agent, and then ask the agent a question rather than find the answer in the help, maybe your help materials aren’t very usable. Maybe increasing the usability of your company’s documentation could alleviate the need users feel to seek answers from another source.