Inverse care law
The inverse care law is the principle that the availability of good medical or social care tends to vary inversely with the need of the population served. Proposed by Julian Tudor Hart in 1971, the term has since been widely adopted. It is a pun on inverse-square law, a term and concept from physics.
The law states that:
"The availability of good medical care tends to vary inversely with the need for it in the population served. This ... operates more completely where medical care is most exposed to market forces, and less so where such exposure is reduced." 
Hart later paraphrased his argument: "To the extent that health care becomes a commodity it becomes distributed just like champagne. That is rich people gets lots of it. Poor people don’t get any of it."
The Inverse Care Law is a key issue in the debate about health inequality. As Frank Dobson put it when he was Secretary of State for Health: "Inequality in health is the worst inequality of all. There is no more serious inequality than knowing that you'll die sooner because you're badly off."
- Tudor Hart, J. (1971). "The Inverse Care Law". The Lancet. 297: 405–412. doi:10.1016/S0140-6736(71)92410-X.
- Watt, G. (2002). "The inverse care law today". The Lancet. 360: 252–254. doi:10.1016/S0140-6736(02)09466-7.
- A Reappraisal of the Inverse Care Law Cooper K., 2010