Study guide: The Short Run: Goods Market

📋 Course Outline

1. GDP Expenditure Components
2. Goods Demand and Consumption
3. Equilibrium Output and Multiplier
4. Investment, Saving, and Equilibrium
5. Thrift and Collective Outcomes
6. Limits of Government Policy

📖 1. GDP Expenditure Components

🔑 Key Concepts & Definitions

• Consumption: The goods and services purchased by consumers.
• Investment: Economic investment (I) consists of fixed investment and inventory investment, not financial investment.
• Government spending: Government purchases of goods and services by federal, state, and local governments, excluding transfers.
• Fixed investment: Fixed investment is the sum of non-residential investment and residential investment.
• Inventory investment: Inventory investment is the difference between goods produced and goods sold in a given year.
• Exports: Exports (X) are purchases of national goods and services by foreigners.
• Imports: Imports (IM) are purchases of foreign goods and services by national agents, including consumers, corporations, and the public sector.

★ Must-know

• Year-to-year economic activity links production, income, and demand: demand changes affect production when prices and wages are fixed, production changes income, and income changes demand.

Further detail

• Net exports, also called the trade balance, equal $X - IM$.

📌 A trade surplus occurs when exports exceed imports, whereas a trade deficit occurs when imports exceed exports.

📖 2. Goods Demand and Consumption

🔑 Key Concepts & Definitions

• Disposable income: Disposable income (YD) is the income remaining after consumers receive government transfers and pay taxes.
• Consumption function: The consumption function C(YD) describes consumption as a function of disposable income and represents consumer behavior.

★ Must-know

📐 Formula - Total goods demand is $Z \equiv C + I + G + X - IM$; in a closed economy, where $X = IM = 0$, it is $Z \equiv C + I + G$.

📐 Formula - The linear consumption function is $C = c_0 + c_1Y_D$, where $0 < c_1 < 1$, c1 is the propensity to consume, and c0 is consumption when disposable income is zero.

📌 Endogenous variables are determined by other variables in a model, whereas exogenous variables are taken as given and not explained within it.

Further detail

• The model assumes one final good that can be used for consumption, investment, or government purchases, and firms supply any amount at price level P, so demand determines output.

• A change in c0 shifts consumption for a given disposable income, and the propensity to consume can be lower for relatively richer households.

📐 Formula - Disposable income is $Y_D \equiv Y - T$, where T is taxes minus government transfers.

• Investment, government spending G, and taxes T are assumed exogenous; G and T represent government fiscal-policy choices.

📖 3. Equilibrium Output and Multiplier

🔑 Key Concepts & Definitions

• Autonomous spending: Autonomous spending is $c_0 + I + G - c_1T$ and does not depend on output.
• Multiplier: The multiplier is $\frac{1}{1-c_1}$ and is larger when the propensity to consume c1 is closer to 1.

★ Must-know

📐 Formula - In a closed economy, goods-market equilibrium requires production to equal demand: $Y = Z = C + I + G$.

📐 Formula - With the linear consumption function, equilibrium output is $Y = \frac{1}{1-c_1}(c_0 + I + G - c_1T)$.

Further detail

• If c1 equals 0.6, the multiplier is 2.5, so an increase in autonomous spending of €1 billion raises output by €2.5 billion.

• 🔄 The graphical equilibrium is determined by:

  1. Plot the 45-degree line where production equals income.
  2. Plot demand as a function of income.
  3. Identify the intersection where production equals demand.

• An increase in autonomous spending raises demand, production, and income in the first round; the added income then generates further demand and successive rounds of production and income.

📐 Formula - After n + 1 rounds, the cumulative output increase relative to the initial spending increase is $1 + c_1 + c_1^2 + \cdots + c_1^n$, which converges to $\frac{1}{1-c_1}$.

• With a propensity to consume of 0.8, an initial demand increase of 100 produces an equilibrium output increase of 500 through successive rounds of spending.

📌 In the model, adjustment is instantaneous, but in reality the time needed for output to adjust depends on how and when firms revise production schedules.

• Unplanned inventory investment (IV) is the difference between actual expenditures $Y = C + I + G$ and planned expenditures $Z = C + I + G$; goods-market equilibrium requires IV = 0.

• Econometrics is the set of statistical methods used in economics, and it can be used to estimate the propensity to consume that determines the multiplier.

📖 4. Investment, Saving, and Equilibrium

🔑 Key Concepts & Definitions

• Private saving: Private saving (S) is the part of disposable income that is not consumed, so $S \equiv Y_D - C = Y - T - C$.
• Public saving: Public saving equals $T - G$; it is positive with a budget surplus and negative with a budget deficit.

★ Must-know

📐 Formula - Goods-market equilibrium can be expressed equivalently as production equals demand, $Y = C + I + G$, or investment equals saving, $I = S + (T - G)$.

Further detail

• In 1936, John Maynard Keynes presented an alternative model focused on investment and saving in The General Theory of Employment, Interest and Money.

📐 Formula - Rearranging the consumption function gives private saving as $S = -c_0 + (1-c_1)(Y-T)$, where $1-c_1$ is the propensity to save and lies between 0 and 1.

• Solving the investment-equals-saving condition for output yields the same equilibrium-output expression as the production-equals-demand approach.

📖 5. Thrift and Collective Outcomes

🔑 Key Concepts & Definitions

• Paradox of thrift: The paradox of thrift is the possibility that attempts by individuals to save more reduce aggregate demand and output, potentially lowering total saving.
• Fallacy of composition: The fallacy of composition is the mistaken assumption that what is true of individual parts must always be true of the whole.
• Prisoners’ dilemma: The prisoners’ dilemma is a game in which each of two prisoners independently chooses whether to cooperate or betray the other, without communication.

★ Must-know

• In this model, consumers attempting to save more by reducing c0 and/or c1 lower equilibrium output; at equilibrium, saving remains determined by investment and the public budget balance if I, T, and G do not change.

Further detail

• In the prisoners’ dilemma described, defection gives each prisoner a higher payoff than cooperation regardless of the other prisoner’s choice, making defection a strictly dominant strategy and mutual defection the only strong Nash equilibrium.

• The course identifies the paradox of thrift as an example of a fallacy of composition and notes its appearance in Bernard Mandeville's The Fable of the Bees: or, Private Vices, Publick Benefits (1714), as noted by Keynes.

💡 Memory Hook

More desired saving lowers demand and output, potentially reducing total saving.

📖 6. Limits of Government Policy

★ Must-know

📌 The equilibrium-output equation implies that government choices of G or T can affect output in the model, but it does not establish that government can achieve any desired output in reality.

Further detail

• Changing government spending or taxes is not easy, and changes in investment and imports can make policy effects difficult for governments to assess.

• Expectations may matter for the effects of fiscal policy.

• Fiscal policy's effects on output may be unsustainable in the medium run.

• Cutting taxes or increasing government spending can lead to large budget deficits and public debt in the long run.