What effect will the following changes have on the equilibrium of the economy? Explain with a diagram. a) Decl

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Q. What effect will the following changes have on the equilibrium of the economy? Explain with a diagram. a) Decline in marginal propensity to consume b) Increase in autonomous consumption.

Jharkhand JacJAC Jharkhand Intermediate Class 12 (Commerce) 2025Subjective· 5mImportance★★★★★

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Concept understanding — Parametric Line Shift

The Everyday Intuition

Imagine you're standing at a bus stop. The bus route is fixed — it always follows the same road. But one day, the bus company decides to move the entire route 200 metres to the east. The road hasn't changed, the bus still travels in a straight line, but every single point on that route has shifted by the same amount in the same direction.

That's a parametric line shift in economics.

Now think of a demand curve. You know that when the price of a good rises, the quantity demanded falls — you move along the curve. That's like walking along the bus route. But what if something else changes — say, your income increases? Then at every price, you now want to buy more of the good. The entire demand curve moves to the right. That's a parametric shift.

Note

Movement along the curve vs shift of the curve:

Movement along = price changes, other things constant.
Shift of the curve = a parameter (like income, tastes, technology) changes.

The Precise Meaning

In economics, a parameter is a factor that is held constant when we draw a curve, but which can change in the real world. For a demand curve, the parameters include:

Consumer income
Prices of related goods (substitutes and complements)
Tastes and preferences
Expectations about future prices

When any of these changes, the entire relationship between price and quantity changes. The curve doesn't just tilt — it shifts parallel (or nearly parallel) to its original position.

Q_d = a - bP

Why It Matters

This distinction is the single most common source of confusion in introductory economics. If you confuse a movement along a curve with a shift of the curve, you'll get every policy question wrong.

Example from NCERT Class 12 Macroeconomics:

When the government increases its spending ( $G$ ), the aggregate demand curve shifts right. That's a parametric shift — the parameter $G$ has changed. If you instead thought that a rise in the price level shifts the AD curve, you'd be wrong: a change in the price level causes a movement along the AD curve, not a shift.

Watch out

Common mistake: "When price falls, demand increases, so the demand curve shifts right."

No — a fall in price moves you down the same demand curve. The curve shifts only when a non-price factor changes.

The Two Key Types of Parametric Shifts

1. Parallel Shift (Change in Intercept) …

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(a) Lower MPC flattens AD and lowers the multiplier → equilibrium income falls; (b) higher autonomous consumption shifts AD up → equilibrium income rises.

Equilibrium income is where aggregate demand (AD = C + I) equals aggregate supply (the 45° line). On the Keynesian-cross diagram, AD = A + bY, where A is autonomous expenditure and b is the MPC (the slope).

(a) Decline in the marginal propensity to consume (MPC):

MPC is the slope of the consumption/AD line, so a fall in MPC makes the AD line flatter.
A lower MPC also means a smaller multiplier (k = 1/(1 − MPC)).
The flatter AD line cuts the 45° line at a lower level of income, so the equilibrium level of income falls (and employment falls). The fall in income is larger than the direct effect because of the reduced multiplier.

(b) Increase in autonomous consumption:

Autonomous consumption is a part of the intercept (A) of the AD line, independent of income.
An increase in it shifts the whole AD line upward (a parallel upward shift).
The new AD line cuts the 45° line at a higher income, so the equilibrium level of income rises. Through the multiplier, income rises by (multiplier × increase in autonomous consumption), i.e. ΔY = k × ΔA. …

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Same / Similar Concept — real previous-year questions on the same or a closely similar concept, not this exact question.

CBSE 2023Set ANNUAL2 marks

Q. Distinguish between Supply Shocks and Stagflation.

›Reveal solution

A supply shock is a sudden, often unexpected, disturbance on the supply side of the economy; stagflation is the macroeconomic condition — simultaneous high inflation and stagnant output/high unemployment — that frequently results from an adverse supply shock.

Basis	Supply Shock	Stagflation
Meaning	A sudden, unanticipated event that changes the availability or cost of a key input (e.g., oil), shifting the Aggregate Supply curve	A sustained macroeconomic situation of high/rising inflation occurring together with stagnant growth and high unemployment
Nature	A cause/triggering event	An outcome/resulting state of the economy
Direction	Usually adverse (e.g., an oil price hike) shifts AS leftward/upward, raising costs	Characterised by simultaneously rising price level AND falling/stagnant output — unlike normal demand-pull inflation where output and prices move together

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Q.What effect will the following changes have on the equilibrium of the economy? Explain with a diagram. a) Decline in marginal propensity to consume b) Increase in autonomous consumption.

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