This idea, that there is such a distinction, has been proven wrong. Economists continue to believe in it. They continue to preach that Economic Theory is Positive, while Economic Policy must be based on normative considerations. There are many lines of attack on conventional economics opened up by this mistake which lies at the heart of modern economics textbooks. Many papers can be produced along these lines.
The Positive Normative Distinction and Its impact on Economic Theory (paper idea)
Link to Current Research which also has material on this issue, under active research
How Values Permeate Economic Theory: Hilary Putnam and his papers/books ideas are crucial here.
Fall of the Two Dichotomies: by Vivian Walsh and Hilary Putnam (attached below)
Some convenient reference materials are:
"Changing Social Ethos is the Key", by John E. Roemer of Yale University, asks if it is too big a task to implement reasonable outcomes, as we consider rewriting financial regulation.
The Economists' Voice, edited by Aaron Edlin and Joseph Stiglitz
Scan of "Towards a Better Understanding of the Positive Normative Distinction" by Samuel Weston. [ in email from hamid hassan gmail aug 28, 2009
Lewin, Peter: "Facts, Values and the Burden of Proof" The Independent Review, v., XI, n. 3, Winter 2007, ISSN 1086-1653, Copyright © 2007, pp. xxx– xxx.
Bruce Caldwell ([1987] 2008). "positivism," The New Palgrave Dictionary of Economics, 2nd Edition. Abstract.
Richard G. Lipsey (2008). "positive economics." The New Palgrave Dictionary of Economics. 2nd Edition. Abstract.