This is an interesting topic and one that goes through considerable research when launching medical products. Personally I have some experience with the human factor research during my time working as a clinical research coordinator for a pain management clinic. The main factor that attributes to errors/misuse of the product is unclear language on packaging. For the most part most clinical trial experiments would run smoothly, however when there were combination products involved some confusion would arise. Even though a specialist is sent in to demonstrate the use of the products, the clinicians would be so busy that when it came time to actually utilizing the product they would have to refer to the packaging instructions and research coordinators for instructions on proper use. This to me represents a design flaw, if the intended user needs to approach external resources for the use of a product. More information on human factors is provided by the FDA in the link attached below.

http://www.fda.gov/downloads/RegulatoryInformation/Guidances/UCM484345.pdf