1. Introduction
Despite the unprecedented expansion of the Federal Reserve and European Central Bank balance sheets after the 2008 crisis, U.S. inflation remained below 2 percent until well into 2021—a phenomenon that
Blanchard and Bernanke (2023)
termed the “great disconnect.” This episode reopens the debate surrounding Friedman’s postulate that inflation is inherently a monetary phenomenon and suggests that the M → π link is mediated by omitted variables.
This paper reformulates the Quantity Theory of Money by incorporating three forces characteristic of the twenty-first century: The real effective exchange rate (REER)—preferred over bilateral exchange rates as it reflects relative prices against a trade-weighted basket of partners (
Engel, 2016
)—globalization (KOF index), and digitalization (IDI). Based on a VAR (3) estimated with quarterly U.S. data from 2000 Q1 to 2024 Q4, the REER is shown to Granger-cause inflation, and a 1 percent real depreciation increases the CPI by 0.21 percentage points after two quarters (p < 0.01). These results, consistent with
Auer, Borio, and Filardo (2017)
on global competition, help explain why QE programs—whose impact on yields is well-documented—did not produce the expected inflation while the dollar remained strong and e-commerce intensified price competition. By incorporating REER, KOF, and IDI, the proposed model offers a more robust framework for evaluating the effectiveness of monetary policy in open, digitalized economies.
Both episodes led to the adoption of a monetary tool that had previously been considered exceptional: quantitative easing (QE), defined as large-scale injections of newly created money through massive asset purchases, with the goal of stabilizing economies emerging from real estate and debt bubbles and preventing deflation. The initial push came from the U.S. Treasury and Federal Reserve; however, the European Central Bank eventually implemented similar expansionary policies. It is often argued that German reluctance toward activist monetary policy stems from a “trauma” rooted in the 1923 Weimar hyperinflation, which continues to influence national attitudes toward price stability (
Barkhausen, 2025
).
Monetarism, formalized in the 1960s by
Friedman and Schwartz (1963)
, has long dominated monetary policy and traces its roots to the sixteenth-century School of Salamanca.
Friedman (1970)
argued that monetary growth in excess of real output inevitably leads to a general rise in prices. Historically, empirical evidence appeared to support this prediction, particularly in earlier crises. However, models with heterogeneous agents show that the effects of monetary expansion depend critically on wealth distribution and the marginal propensity to consume (
Kaplan, Moll, & Violante, 2018
), helping to explain the limited transmission mechanisms observed after 2008.
This empirical paradox weakened monetarist orthodoxy and paved the way for alternative frameworks, such as Modern Monetary Theory (MMT). According to
Kelton (2020)
, the post-crisis experience shows that sustained money creation by central banks does not automatically lead to inflation. While the puzzle gave rise to MMT, it also spurred new explanations based on global savings gluts and secular stagnation (
Blanchard, 2016
), both consistent with persistently low money velocity.
Mainstream scholars attributed the absence of inflation to the collapse in money velocity due to deleveraging and precautionary savings. However, this explanation proves insufficient. In today’s globalized economy, integrated value chains have increased the elasticity of global supply; demand shocks are absorbed by relocatable production and declining price pass-through (
Auer, Levchenko, & Sauré, 2019
). Recent studies have found that the pass-through from exchange rates to CPI inflation weakened significantly after the global financial crisis (
Jasova et al., 2016
). When QE is implemented simultaneously among trading partners, the REER tends to remain stable, neutralizing its inflationary effect. Simultaneously, the digitalization of commerce and logistics increases price transparency and competition. Globalization and digitalization thus operate as persistent structural deflationary forces.
This paper proposes a reformulated version of the QTM that preserves the foundational role of money supply and velocity but incorporates three key twenty-first-century forces: the REER, globalization (KOF index), and digitalization (IDI). The model adopts a log-log specification, allowing for the estimation of proportional elasticities of each factor on inflation. The contribution to the literature is twofold: 1) it introduces the first structural version of the QTM that incorporates REER, KOF, and IDI, and 2) it empirically demonstrates its superior forecasting performance compared to the classical monetarist model and a Phillips-curve VAR.
To support this proposal with rigorous evidence, a VAR (3) including inflation, M2 growth, and the real effective exchange rate (REER) is estimated using U.S. quarterly data from 2000 Q1 to 2024 Q4. Granger causality tests confirm a bidirectional relationship between REER and inflation (χ2 = 18.6; p < 0.01), and a unidirectional relationship from M2 to prices. These findings are consistent with the literature on exchange rate pass-through in open economies (
Choudhri & Hakura, 2006
: Journal of International Economics;
Forbes, Hjortsoe, & Nenova, 2018
: Economic Journal). The REER is used—instead of a bilateral rate such as USD/EUR—because it aggregates movements against a trade-weighted basket of partners and adjusts for inflation differentials, providing a more accurate measure of external competitiveness and domestic price dynamics (
Darvas, 2012
;
Iossifov & Fei, 2019
). This evidence reinforces the case for including the REER as a structural variable in a modern reformulation of the QTM.
The REER is employed—rather than a nominal bilateral exchange rate—because it captures competitiveness against a trade-weighted basket of partners and adjusts for inflation differentials, thereby avoiding distortions caused by idiosyncratic shocks. This allows the model to reflect the effective cost of imports and the real appreciation of foreign goods that affects domestic CPI, in line with the paper’s objective of linking trade openness and price formation. (Data sources, VAR specification, and robustness tests are detailed in Section 3.)
Using U.S. quarterly data from 2000 to 2024, the study evaluates whether this extended framework outperforms the classical model in both internal fit and economic interpretation. The central hypothesis is that REER, globalization, and digitalization now operate as persistent deflationary forces: the first intensifies price competition in tradables (
IMF, 2020
), while the latter reduces margins and search costs via digital platforms and automation (
OECD, 2022
). By calibrating and comparing both models during shocks such as the 2008 crisis and the COVID-19 pandemic, the paper assesses whether the new specification offers a better account of recent inflation dynamics.
Moreover, it is shown econometrically—through a VAR(3) with unit-root corrections—that REER Granger-causes inflation in the U.S. (p < 0.01), whereas the reverse causality weakens once monetary supply is controlled for. The REER is adopted because it reflects net external competitiveness across multiple partners and avoids the bilateral bias of the U.S. dollar (
Engel, 2016
). Recent studies report that its pass-through to domestic prices ranges from 30 to 50 percent over two-year horizons (
Gopinath & Itskhoki, 2022
).
The remainder of the paper is structured as follows: Section 2 reviews the theoretical foundations and introduces the exchange rate, globalization, and digitalization channels; Section 3 presents the data and econometric methodology; Section 4 reports the empirical results and robustness checks; Section 5 discusses policy implications; and Section 6 concludes and outlines directions for future research.
2. Theoretical Review
2.1. Foundations of Classical Monetarism
The Quantity Theory of Money (QTM) traces its origins to the School of Salamanca, where Martín de Azpilcueta and Jean Bodin first linked the abundance of precious metals to rising prices.
Fisher (1911)
formalized this intuition with the equation of exchange, M·V = P·Y, and Milton Friedman—along with Anna Schwartz (
Friedman & Schwartz, 1963
)—popularized it by asserting that “inflation is always and everywhere a monetary phenomenon.” The core of this framework rests on two key assumptions:
These ideas laid the groundwork for central bank independence and the adoption of simple policy rules—such as Friedman’s k-percent rule or Taylor’s rule—to manage the money supply.
2.2. Empirical Challenges after 2008
The Global Financial Crisis of 2008 disrupted this framework. Although the balance sheets of the Federal Reserve, the ECB, the BoJ, and the BoE expanded dramatically, inflation remained subdued. Three classical monetarist explanations were called into question:
1) Collapse in money velocity: Massive deleveraging and a heightened preference for liquidity caused excess reserves to remain “parked” in commercial banks.
2) Liquidity trap: With interest rates at the zero lower bound, conventional monetary policy lost traction, and credit transmission stalled.
3) Anchored expectations: Central banks retained credibility and prevented inflation expectations from rising, thereby dampening price sensitivity to monetary base expansion.
These developments paved the way for explanations that extend beyond the traditional M → P mechanism.
2.3. The Exchange Rate Channel and Evidence of Causality
The pass-through literature suggests that real depreciation increases import prices and gradually transmits to domestic inflation (
Taylor, 2000
). Granger causality tests based on third-order vector autoregressions (VAR(3)) confirm that for the United States (1970-1980) and Türkiye (2005-2024), the REER Granger-causes inflation with lags of two to four quarters, while reverse causality is weaker. This evidence supports the use of the Real Effective Exchange Rate (REER) over nominal indicators: the REER adjusts for price differentials and better captures external competitiveness.
2.4. Globalization and Digitalization as Deflationary Forces
Since the 1990s, two structural transformations have compressed profit margins and prices:
Recent meta-analyses conclude that each deviation of the IDI or KOF above trend exerts deflationary elasticities on the CPI ranging from –0.10 to –0.40.
2.5. Structural Reformulation in Log-Log Form
To integrate these forces, this study proposes the Structural Quantity Theory Model (SQTM):
(1)
where:
Each βj coefficient is interpreted as an elasticity: a 1% increase in variable j changes inflation by βj% ceteris paribus.
The multiplicative specification captures the idea that proportional shocks to each variable result in proportional changes in inflation. The log-log transformation linearizes this relationship—allowing each βi to be interpreted as an elasticity—facilitates estimation using Generalized Least Squares (GLS), and mitigates heteroskedasticity.
The parameter α captures the unexplained equilibrium level of inflation, while εt accounts for idiosyncratic shocks.
2.6. Dynamic Predictions
Taken together, this revision shows that while the QTM remains a valid starting point, it must be expanded to incorporate structural variables that act as “amplifiers” or “buffers” of the traditional monetary mechanism. The SQTM offers both a theoretical and empirical bridge, explaining why the quantitative expansions of the past decade did not lead to proportional inflation, and signaling to central banks that, in the twenty-first century, monitoring REER, KOF, and IDI is as essential as tracking M2 and money velocity.