Determination of Income and Employment

The One Thing

The equilibrium level of national income and employment is determined where aggregate demand equals aggregate supply. Because aggregate demand depends principally on consumption and investment, changes in these components can generate multiplied changes in income and can produce full-employment, underemployment, inflationary, or deflationary outcomes.

Who and What

• Aggregate Demand (AD): The total planned expenditure on final goods and services during a given period. In a Two-Sector Model containing households and firms, with no government or foreign sector, AD = C + I, where C is consumption expenditure and I is investment expenditure. In a more complete economy, AD = C + I + G + (X − M).
• Aggregate Supply (AS): The total value of goods and services produced during a given period. In the simple income model, AS is represented by national income, Y.
• Consumption Function: The relationship between consumption expenditure and income, expressed as C = C̄ + bY. C̄ is autonomous consumption and b is the marginal propensity to consume.
• Autonomous Consumption: Consumption undertaken even when income is zero, usually financed through savings or borrowing.
• Induced Consumption: Consumption that changes with income, represented by bY in the consumption function.
• Saving: The part of income that is not consumed. The relationship is S = Y − C, so consumption and saving are complementary: Y = C + S.
• Saving Function: If C = C̄ + bY, then S = −C̄ + (1 − b)Y.
• Average Propensity to Consume (APC): The ratio of consumption to income: APC = C/Y.
• Marginal Propensity to Consume (MPC): The ratio of the change in consumption to the change in income: MPC = ΔC/ΔY.
• Average Propensity to Save (APS): The ratio of saving to income: APS = S/Y.
• Marginal Propensity to Save (MPS): The ratio of the change in saving to the change in income: MPS = ΔS/ΔY.
• Relationship between MPC and MPS: Since additional income is either consumed or saved, MPC + MPS = 1. Likewise, APC + APS = 1. In the usual model, MPC lies between 0 and 1.
• Equilibrium Level of Income: The level of income at which planned aggregate demand equals aggregate supply. The equilibrium condition is AD = AS, or Y = C + I. Using C = C̄ + bY, equilibrium income is Y = (C̄ + I)/(1 − b), assuming investment is autonomous.
• Ex Ante and Ex Post: Ex ante refers to planned or intended values. Ex post refers to actual values after economic activity has occurred. Planned saving and planned investment are equal at equilibrium, S = I, while actual or ex post saving and investment are equal by accounting identity.
• Multiplier: The ratio of the change in income to the initial change in investment: K = ΔY/ΔI = 1/(1 − MPC) = 1/MPS. Its value is greater than 1 when MPC is positive.
• Full Employment: A situation in which all people willing and able to work at the prevailing wage rate obtain employment, apart from normal frictional or voluntary unemployment.
• Involuntary Unemployment: A situation in which people are willing and able to work at the existing wage rate but cannot find employment.
• Underemployment Equilibrium: An equilibrium below the full-employment level of income, where AD equals AS but some resources remain unemployed.
• Effective Demand: The level of aggregate demand at which entrepreneurs expect to sell their output profitably. It determines equilibrium employment and income.
• Excess Demand: A situation in which aggregate demand exceeds the output corresponding to full employment. It creates an inflationary gap and upward pressure on prices.
• Inflationary Gap: The excess of planned aggregate demand over the level required to purchase full-employment output.
• Deficient Demand: A situation in which aggregate demand is below the output corresponding to full employment. It creates a deflationary gap, unemployment, and downward pressure on prices.
• Deflationary Gap: The shortfall of planned aggregate demand from the level required to purchase full-employment output.

Causes and Consequences

• Effective demand determines production and employment. Firms produce and employ workers according to the level of demand they expect for their output. Equilibrium is therefore established where AD = AS, or Y = C + I in the simple two-sector economy.

• Consumption and saving determine the distribution of income. Since Y = C + S, income not spent on consumption is saved. At the break-even level of income, consumption equals income and saving is zero. Below this level, dissaving may occur; above it, positive saving generally occurs.

• Equilibrium can be expressed through saving and investment. At equilibrium, planned saving equals planned investment: S = I. This condition corresponds to AD = AS, although actual or ex post saving and investment are equal by accounting identity.

• Autonomous investment produces a multiplied change in income. An initial increase in investment raises the income of those receiving the expenditure. Their additional consumption then becomes income for others, creating successive rounds of consumption and income generation. This process occurs because one person’s expenditure becomes another person’s income.

• The size of the multiplier depends on the MPC. The multiplier is K = ΔY/ΔI = 1/(1 − MPC) = 1/MPS. A higher MPC produces a larger multiplier because a greater share of each additional income round is spent on consumption.

• The numerical example demonstrates the multiplier effect. If MPC = 0.8, then MPS = 0.2 and K = 1/0.2 = 5. An increase in investment of ₹100 crore can therefore raise equilibrium income by ₹500 crore, assuming other conditions remain unchanged.

• The multiplier depends on restrictive assumptions. The investment multiplier assumes constant prices, unused productive capacity, a stable MPC, no time delays, and no changes in taxes, imports, or interest rates. If these conditions change, the actual increase in income may differ from the simple multiplier result.

• Equilibrium does not necessarily imply full employment. If aggregate demand is insufficient, the economy may settle at an underemployment equilibrium, in which AD equals AS while involuntary unemployment and unused resources remain.

• Full-employment equilibrium occurs when demand supports full-employment output. Full employment exists when aggregate demand equals aggregate supply at the full-employment level of output and all willing and able workers can obtain employment, apart from normal frictional or voluntary unemployment.

• Excess demand creates an inflationary gap. When planned aggregate demand exceeds the level required to purchase full-employment output, the economy experiences excess demand. Once resources are fully employed, this generally creates inflationary pressure rather than a sustained increase in real output.

• Deficient demand creates a deflationary gap. When planned aggregate demand falls below the level required to purchase full-employment output, deficient demand causes reduced output, income, and employment, as well as unemployment and downward pressure on prices.

• Policy can correct demand imbalances. To reduce excess demand, authorities may reduce government expenditure, increase taxes, reduce the money supply, or raise interest rates. To correct deficient demand, they may increase government expenditure, reduce taxes, increase the money supply, or lower interest rates. Fiscal policy and monetary policy can therefore move the economy towards full-employment equilibrium.

What Gets Asked

• Explain how equilibrium income is determined using AD = AS and Y = C + I, including the derivation of Y = (C̄ + I)/(1 − b).
• Distinguish between autonomous and induced consumption, and explain the relationships among APC, APS, MPC, and MPS.
• Explain the multiplier process and calculate its value, including the example where MPC = 0.8, MPS = 0.2, K = 5, and an investment increase of ₹100 crore raises income by ₹500 crore.
• Compare full-employment equilibrium with underemployment equilibrium, including the role of involuntary unemployment.
• Distinguish between excess demand and deficient demand, and relate each to inflationary or deflationary gaps, output, employment, and prices.
• Evaluate the assumptions and limitations of the investment multiplier and assess the use of fiscal and monetary policy to correct demand deficiencies or excess demand.