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This overview of intertemporal choice explores key concepts from microeconomics, including budget constraints and the Discounted Utility Model. It examines how individuals make consumption decisions across different periods, influenced by savings, borrowing, and interest rates. The interplay between present and future values dictates financial behaviors, affecting overall economic stability. By analyzing these dynamics, this text offers insight into individual and governmental strategies for consumption regulation, particularly during interest rate fluctuations.
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Microeconomics 2 John Hey
Intertemporal Choice • Chapter 20 – the budget constraint, intertemporal preferences in general and choice in general • Chapter 21 –intertemporal preferences in particular – the Discounted Utility Model • Chapter 22 – intertemporal exchange
A question for you • An observation: to reduce consumption in an economy, the government usually raises the interest rate. Why? • If interest rates rise … • … an individual is better or worse off? • … saves more or less? • … spends more or less? • The correct answers?.... • … it depends…
Framework • Intertemporal choice. • Two periods: 1 and 2. • We consider an individual who receives an income in each of the two periods. • Might be happy to consume his or her income in the period in which it is received ... • ... but might prefer to re-distribute it, by saving or borrowing. • That is what these three chapters of the book are about. • (We have already talked about allocation within a period to specific goods and services. Here we are talking about allocation between periods.) • But first some preliminaries about saving and borrowing, rates of interest and rates of return.
Notation and graphical representation • Intertemporal choice. • Two periods: 1 and 2. • m1 and m2: incomes in the two periods. • c1 and c2: consumption in the two periods. • r: the rate of interest (10%, r = 0.1; 20%, r = 0.2) • The rate of return = (1+r) • We will be drawing graphs with c1 and c2 on the axes, and (m1, m2) as the endowment point. • First the budget constraint then the preferences.
The Budget Line 1. • m1 > c1 savings = m1 - c1 • Becomes (m1 - c1)(1+r) in period 2. • Hence c2 = m2 + (m1 - c1)(1+r). • Or: c1(1+r) +c2 = m2 + m1(1+r). • In the space (c1 ,c2) a line with slope -(1+r).
The Budget Line 2. • m1 < c1 borrowings = c1 - m1 • Have to repay (c1 - m1)(1+r) in period 2. • Hence c2 = m2 - (c1 - m1)(1+r). • Or: c1(1+r) +c2 = m2 + m1(1+r). • In the space (c1 ,c2) a line with slope -(1+r).
The Budget Line 3. • maximum consumption in period 2 = m1(1+r) + m2 • – this is called the future value of the stream of income. • maximum consumption in period 1 = m1 + m2/(1+r) • – this is called the present value of the stream of income. • Note: we say that the market discounts the income in period 2 at the rate r.
The Budget Line 4. • The intercept on the horizontal axis = • m1 + m2/(1+r) – the present value of the stream of income.. • The intercept on the vertical axis = • m1(1+r) + m2 – the future value of the stream of income... • The slope = -(1+r)
Generalisation • If the individual receives a stream of income: • m1, m2, m3 … mT • The present value is • The future value is
Chapter 20 • Let us go briefly to the Maple Chapter 20, but note... • ... most of Chapter 20 uses general preferences. (So do not spend too much time on studying the rest of this Chapter.) • But it shows that saving and borrowing depend upon incomes and rate of interest. • In Chapter 21 we use Discounted Utility Model preferences.
Chapter 20 • Goodbye!