1. Beckworth D.&Selgin G.(2010).Where the Fed Goes Wrong: The ‘Productivity Gap’ and Monetary Policy. Working paper 20 April.http://econfaculty.gmu.edu/pboettke/workshop/Spring2010/Beckworth2.pdf(accessed 14 February 2019).
2. Binder C.(2015).Did the natural rate fall? Quantitative Ease 30 October.http://carolabinder.blogspot.com/2015/10/did-natural-rate-fall.html(accessed 14 February 2019).
3. THE EQUILIBRIUM FED FUNDS RATE AND THE INDICATOR PROPERTIES OF TERM-STRUCTURE SPREADS
4. Brand C. Bielecki M. &Penalver A.(2018).The Natural Rate of Interest: Estimates Drivers and Challenges to Monetary Policy. ECB Occasional Paper No. 217.Frankfurt:European Central Bank.
5. Browne F. &Everett M.(2006).The Real Interest Rate Spread as a Monetary Policy Indicator. Research Technical Paper No. 06/06.Dublin:Central Bank of Ireland.