Only recently have researchers been able to do something that approaches empirical studies. The data is showing some new things but also confirming some old wisdom. Most things are done by a very small percentage of the people. It applies to good things like innovation and bad things like crime or consumption of medical care. For example, 1% of the patients is 30% of the payments to the hospitals, and that 5% of the patients is about 50% of the payments to the hospital. You can address half your costs by targeting a very small part of the population.
Reference – http://freakonomics.com/2015/04/02/how-do-we-know-what-really-works-in-healthcare-a-new-freakonomics-radio-podcast/