Maslow's Heirarchy of Needs (shown below) is a popular concept and is often taught in basic psychology courses, and often less objectively taught in Business and Marketing courses.
A common problem with Maslow's Hierarchy is the difficulty of testing the theory and the ordering and definition of needs.
The Wikipedia article and most general sources about the topic do not discuss experimental tests regarding the Hierarchy nor am I familiar with any despite the theory's popularity.
What research exists that investigates Maslow's Hierarchy directly?

