What if rather than mathematical economic formula's and double speak, we just looked at the population of potential workers, by age groups, and employment among them. Then cross reference against the Federal Reserve set Fed Funds rate, Federal Reserve purchased assets, and the debt these policies incentive (I'll focus on federal debt, but the same is true for corporations, individuals).
What is plain? There was a period of economic growth via population growth, a period of growth via increasing participation among females, and now a period of "pseudo growth" via ZIRP, QE, and unrepayable federal debt accrual. And every time the economy hit "full employment" whereupon no further slack or potential employees are available, an economic crisis is declared. What is also obvious is the interplay of ZIRP, QE, and debt to inflate asset prices. All of the rate cuts, QE, and debt are undertaken to purportedly achieve the Fed's mandate of "full employment" but nearly all the real benefits flow to a shrinking cadre of institutional and elderly asset holders. As for the poor, young adults, retirees living on fixed incomes...they are all punished via costs of living rising far faster than incomes thanks to the flow through of the higher asset prices.
25 to 54 year old Population / Employees
25 to 54 year old population (blue line) vs. those employed among them (green line), Fed Funds Rate % (dashed black line), Federal Reserve assets (yellow line), and US federal government marketable Treasury debt (red shaded area).
1- Population growth decelerates into and through 2007...and entirely ceases thereafter.
2- 25 to 54 year old employment growth ends as of 2000, and has been essentially flat-lining for twenty years.
3- Fed funds rate essentially moves inverse the population/employment rate of growth...rising as rate of growth accelerated and falling as growth decelerated...and then turned ZIRP as population/employment ceased growth.
4- From 1981, as population/employment growth decelerated, the Fed Funds Rate was consistently cut to encourage the substitution of debt for the decelerating growth. But since 2007, as population/employment growth no longer existed, ZIRP plus QE were abused to encourage the explosion of unrepayable debt...and debt that can only be serviced at ZIRP or more likely NIRP.