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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.
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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!