23.01.15 · economics / monetary

Inflation and Deflation

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Anchor (Master): Woodford, Interest and Prices; Friedman & Schwartz, A Monetary History

Intuition [Beginner]

Inflation means a general, sustained increase in prices across the economy. A single product getting more expensive is not inflation -- it might reflect a supply shortage or higher demand for that product alone. Inflation is when the prices of most goods and services rise together, meaning each unit of currency buys less than before.

Deflation is the opposite: a general, sustained decrease in prices. This sounds good for consumers (things get cheaper!), but it can be dangerous. When prices are falling, people delay purchases (why buy today if it will be cheaper tomorrow?), businesses cut production and lay off workers, debts become harder to repay (you owe the same dollars but earn fewer of them), and a downward spiral can develop.

The most common measure of inflation is the Consumer Price Index (CPI), which tracks the cost of a fixed "basket" of goods and services that a typical household buys. If the basket cost $500 last year and $515 this year, inflation is 3%.

Moderate, predictable inflation (around 2% per year) is considered normal and even healthy by most economists. It gives the central bank room to lower interest rates during a recession, and it allows real wages to adjust downward (if needed) without cutting nominal wages, which workers resist. High, unpredictable inflation erodes savings, distorts investment decisions, and hits fixed-income households hardest. Hyperinflation (prices rising by thousands of percent per year) can destroy an economy entirely.

Visual [Beginner]

  Inflation Rate Over Time (hypothetical)
  
  %
  |           
  |              /\         Hyperinflation
  |             /  \        (50%+ per month)
  |            /    \
  |     /\    /      \
  15%--/  \--/        \     High inflation
  |                 \  \
  |      moderate    \  \
  5%--- inflation     \  \
  |   (2-5%)           \  \
  2%--------------------\--\---- Target (many central banks)
  |                      \  \     Deflation
  0%----------------------\--\---- Zero
  |                        \  \_/_ below zero
  -2%                         
  +---------------------------- Year

  Winners and Losers from Unanticipated Inflation:
  
  LOSES                          GAINS
  Savers (real value falls)      Borrowers (repay in cheaper dollars)
  Fixed-income earners           Asset holders (real assets rise)
  Lenders (repaid in             Government (real debt burden falls)
    cheaper dollars)

Worked Example [Beginner]

Measuring Inflation with CPI:

A consumer price index tracks a basket of goods:

Item	Qty	Price (Year 1)	Price (Year 2)	Price (Year 3)
Bread	10	$2.00	$2.20	$2.30
Gas	20	$3.00	$3.60	$3.00
Rent	1	$800	$840	$880

Year 1 (base year) cost: $10 \times $2 + 20 \times $3 + 1 \times $800 = $20 + $60 + $800 = $880$

Year 2 cost: $10 \times $2.20 + 20 \times $3.60 + 1 \times $840 = $22 + $72 + $840 = $934$

Year 3 cost: $10 \times $2.30 + 20 \times $3.00 + 1 \times $880 = $23 + $60 + $880 = $963$

CPI and Inflation Rate:

Year	Basket Cost	CPI (Year 1 = 100)	Inflation Rate
1	$880	100.0	--
2	$934	106.1	6.1%
3	$963	109.4	3.1%

Inflation from Year 1 to Year 2: $($934 - $880) /$880 = 6.1%$

Real vs. Nominal: If your wage was $40,000 in Year 1 and $42,000 in Year 2, the nominal increase is 5%, but real wages fell by 1.1% because prices rose 6.1%.

Check Your Understanding [Beginner]

Formal Definition [Intermediate+]

Measuring Inflation

The inflation rate is the percentage change in a price index over a period:

$π_{t} = \frac{P _{t} - P _{t - 1}}{P _{t - 1}} \times 100$

where $P_{t}$ is the price index at time $t$ .

Consumer Price Index (CPI): A Laspeyres index that measures the cost of a fixed basket of goods:

$C P I_{t} = \frac{\sum _{i} p _{i, t} \cdot q _{i, 0}}{\sum _{i} p _{i, 0} \cdot q _{i, 0}} \times 100$

where $p_{i, t}$ is the price of good $i$ at time $t$ and $q_{i, 0}$ is the quantity of good $i$ in the base-period basket.

CPI biases: The Laspeyres index overstates inflation because it does not account for:

Substitution bias: Consumers switch to relatively cheaper goods when prices change.
New goods bias: New products are not immediately included.
Quality change bias: Price increases may reflect quality improvements.

The GDP Deflator is a Paasche index that uses current-period quantities:

$GDP Deflator_{t} = \frac{Nominal GDP _{t}}{Real GDP _{t}} \times 100$

It covers all domestically produced goods and services (not just consumer goods) and automatically accounts for changing consumption patterns, but does not include imported goods.

Types of Inflation

Demand-pull inflation: Aggregate demand exceeds the economy's productive capacity.

$A D > Y^{*} ⟹ P ↑$

The economy is "too much money chasing too few goods." Characterized by rising output and rising prices (moving along the short-run aggregate supply curve).

Cost-push inflation: Rising production costs (wages, raw materials) shift the aggregate supply curve inward.

$A S ↓ ⟹ P ↑, Y ↓$

Characterized by rising prices and falling output ("stagflation" when combined with stagnation).

Built-in (expectations-augmented) inflation: Workers and firms set wages and prices based on expected inflation. If everyone expects 5% inflation, wages and prices rise 5%, producing 5% inflation -- a self-fulfilling prophecy. The expectations-augmented Phillips Curve captures this:

$π_{t} = π_{t}^{e} - β (u_{t} - u_{n}) + ϵ_{t}$

where $π_{t}^{e}$ is expected inflation, $u_{t}$ is the unemployment rate, $u_{n}$ is the natural rate, and $ϵ_{t}$ is a supply shock.

The Fisher Equation

The relationship between nominal interest rates, real interest rates, and inflation:

$i = r + π^{e}$

where $i$ is the nominal interest rate, $r$ is the real interest rate, and $π^{e}$ is expected inflation. The ex-post real rate is $r = i - π$ .

Quantity Theory of Money

$M V = P Y$

In growth rates: $%Δ M + %Δ V = %Δ P + %Δ Y$

If velocity is stable ( $%Δ V = 0$ ) and output is at full employment ( $%Δ Y$ is determined by real factors), then:

$%Δ P = %Δ M - %Δ Y$

Inflation equals money supply growth minus real output growth.

Key Concepts [Intermediate+]

CPI: Consumer Price Index. Tracks the cost of a fixed basket of consumer goods. The most widely cited inflation measure.
GDP Deflator: A broader price index covering all domestically produced output. Uses current-period weights.
Demand-pull inflation: Inflation caused by excess aggregate demand relative to productive capacity.
Cost-push inflation: Inflation caused by rising production costs (supply shocks, wage pushes).
Hyperinflation: Extremely rapid inflation, conventionally defined as exceeding 50% per month. Destroys money's function as a store of value and unit of account.
Deflationary spiral: Falling prices leading to reduced spending, lower production, job losses, and further price declines. Self-reinforcing and difficult to reverse.
Real vs. nominal: Real values are adjusted for inflation; nominal values are not. Real wage = Nominal wage / Price level.
Fisher equation: $i = r + π^{e}$ . Links nominal interest rates to real rates and expected inflation.
Phillips Curve: The short-run trade-off between inflation and unemployment. In the long run, the Phillips Curve is vertical at the natural rate of unemployment (no trade-off).

Exercise 1. The money supply grows at 8% per year, velocity is constant, and real GDP grows at 3% per year. What is the inflation rate? If the central bank wants to reduce inflation to 2%, what should happen to money supply growth?

Exercise 2. A one-year bond offers a nominal yield of 7%. Expected inflation is 4%. What is the expected real return? If actual inflation turns out to be 6%, what is the realized real return? Who gains and who loses relative to expectations?

Academic Perspectives [Master]

Monetarist View

Milton Friedman (1963) argued that "inflation is always and everywhere a monetary phenomenon." Sustained inflation requires sustained growth in the money supply. The Quantity Theory, $M V = P Y$ , implies that in the long run, changes in $M$ translate one-for-one into changes in $P$ , holding $V$ and $Y$ constant.

Friedman advocated for a k-percent rule: the central bank should increase the money supply at a constant rate equal to the long-run growth rate of real output, ensuring stable prices. Discretionary monetary policy, he argued, creates more instability than it resolves due to "long and variable lags."

Critique: The relationship between monetary aggregates and inflation broke down in many countries after the 1980s. Velocity became unstable, financial innovation changed the definition of "money," and many central banks abandoned monetary targeting in favor of interest rate targeting.

Keynesian Perspective

Keynesians view inflation as arising from excess aggregate demand relative to supply capacity. In the short run, an overheating economy (output above potential) generates inflationary pressure. The Phillips Curve captures the trade-off: lower unemployment comes at the cost of higher inflation.

The expectations-augmented Phillips Curve (Friedman, 1968; Phelps, 1968) -- developed by monetarists but incorporated into Keynesian models -- shows that the short-run trade-off exists only when inflation expectations differ from actual inflation. Once expectations adjust, the trade-off vanishes, and the economy returns to the natural rate of unemployment.

Modern New Keynesian models (Woodford, 2003) embed the Phillips Curve in a dynamic stochastic general equilibrium (DSGE) framework:

$π_{t} = β E_{t} [π_{t + 1}] + κ x_{t} + u_{t}$

where $x_{t}$ is the output gap and $u_{t}$ is a cost-push shock. Inflation depends on expected future inflation and current economic slack.

Critique: The Phillips Curve relationship has weakened empirically since the 1990s, leading to the " Phillips Curve puzzle." The relationship between unemployment and inflation is less stable than the model predicts.

Austrian School

Austrian economists reject the aggregate models used by both monetarists and Keynesians. Following Mises (1912), they argue that inflation is not a uniform rise in prices but a distortion of relative prices caused by credit expansion. New money enters the economy at specific points (typically through bank lending to favored sectors), bidding up prices in those sectors first and creating malinvestment. The resulting boom-bust cycle is the real cost of inflation, not the rise in the general price level per se.

Mises distinguished between credit expansion (new money created through fractional reserve lending) and genuine savings. Only the latter can sustainably fund investment. Credit expansion produces an illusion of prosperity that inevitably collapses.

Critique: The Austrian framework has been criticized for its resistance to formal modeling and empirical testing, making it difficult to evaluate against alternatives.

Marxian Perspective

Marx's analysis of money and prices, developed in Capital Vol. I, grounds the price level in the value of money (the socially necessary labor time embodied in the money commodity). Under a gold standard, rising prices could result from a decline in the value of gold (e.g., new gold discoveries). Under fiat money, inflation represents a deterioration in the value of the currency.

Marxian economists have analyzed inflation in terms of class conflict over the distribution of income: workers push for higher wages, firms pass on higher costs through higher prices, and the resulting wage-price spiral generates inflation. This "conflict theory of inflation" views inflation as a symptom of the underlying struggle over the wage share of national income.

Critique: This explanation does not account for periods of low inflation despite ongoing wage pressures, nor for inflation in economies with weak labor movements.

Structuralist View

Structuralist economists, prominent in Latin America (Prebisch, 1950; Furtado, 1963), argue that inflation in developing countries is caused by structural rigidities: agricultural bottlenecks, foreign exchange constraints, unequal income distribution, and institutional factors. These structural features create persistent inflationary pressure that cannot be resolved by monetary policy alone. Orthodox stabilization programs (tight money, fiscal austerity) reduce inflation by causing recession and unemployment, without addressing the underlying causes.

Critique: The structuralist view was used to justify persistent fiscal deficits and accommodative monetary policy in several Latin American countries, contributing to episodes of very high inflation and hyperinflation (Argentina, Brazil). Critics argue that the structural explanation understates the role of monetary expansion.

Historical Context [Master]

Price revolution (16th century): The influx of gold and silver from the Americas into Europe caused sustained inflation, an early example of the quantity theory in action.
Hyperinflation in Germany (1921-1923): The Weimar government printed money to finance reparations and social spending. Prices doubled every few days. At the peak, a loaf of bread cost billions of marks. The episode discredited expansionary monetary policy for a generation and contributed to the political instability that brought the Nazi Party to power.
Great Deflation (1873-1896): A sustained period of falling prices in many countries, driven by rapid productivity growth and the gold standard's constraint on money supply. Deflation benefited creditors and wage earners but hurt debtors (including many farmers), fueling political movements for silver coinage (the "Free Silver" movement in the US).
The Great Inflation (1965-1982): The United States and other developed countries experienced sustained high inflation, peaking at over 13% in 1980. Causes included expansionary fiscal and monetary policy, oil price shocks (1973, 1979), and the collapse of the Bretton Woods system. Paul Volcker's Fed raised interest rates to nearly 20%, inducing a severe recession but breaking inflationary expectations.
Japanese deflation (1990s-2010s): After the collapse of its asset price bubble in 1990, Japan experienced persistent deflation and stagnation. Despite near-zero interest rates and massive fiscal stimulus, the Bank of Japan struggled to achieve its 2% inflation target -- a cautionary example of the difficulty of reversing deflationary expectations.
Great Moderation (1980s-2007): A period of low, stable inflation in developed countries, attributed to improved central bank credibility, inflation targeting, and structural changes in the economy.
Post-2008 and post-2020 inflation: After more than a decade of below-target inflation, the COVID-19 pandemic (2020) and subsequent supply chain disruptions, fiscal stimulus, and energy price shocks drove inflation to multi-decade highs in 2021-2023, reigniting debates about the causes and appropriate policy response to inflation.

Bibliography [Master]

Friedman, M. (1968). The role of monetary policy. American Economic Review, 58(1), 1-17.
Friedman, M., & Schwartz, A. J. (1963). A Monetary History of the United States, 1867-1960. Princeton University Press.
Furtado, C. (1963). The Economic Growth of Brazil. University of California Press.
Mises, L. von (1912). The Theory of Money and Credit. Duncker & Humblot.
Phelps, E. S. (1968). Money-wage dynamics and labor-market equilibrium. Journal of Political Economy, 76(4), 678-711.
Prebisch, R. (1950). The Economic Development of Latin America and Its Principal Problems. United Nations.
Sargent, T. J. (1982). The ends of four big inflations. In R. E. Hall (Ed.), Inflation: Causes and Effects. University of Chicago Press.
Woodford, M. (2003). Interest and Prices: Foundations of a Theory of Monetary Policy. Princeton University Press.