Unit 5: Consumption and Investment Function - Subjective Questions

Meaning: The consumption function shows the relationship between consumption expenditure and disposable income. It explains how much households spend at different levels of income.

The general form is:

where:

• = consumption expenditure
• = autonomous consumption, which occurs even when income is zero
• = marginal propensity to consume (MPC)
• = disposable income

Consumption usually rises when income rises, but it generally increases by less than the increase in income. The slope of the consumption function is the MPC, expressed as:

Thus, the consumption function is an important tool for analyzing household spending and aggregate demand.

Average Propensity to Consume (APC): APC refers to the proportion of total disposable income spent on consumption.

Marginal Propensity to Consume (MPC): MPC refers to the proportion of an additional unit of income spent on additional consumption.

The major differences are:

• APC is calculated using total consumption and total income.
• MPC is calculated using changes in consumption and income.
• APC may be greater than, equal to, or less than one.
• MPC normally lies between zero and one.

For example, if income increases by and consumption increases by , then .

Keynes's psychological law of consumption states that as income increases, consumption also increases, but at a slower rate than the increase in income.

Its main features are:

• Consumption is positively related to income.
• The increase in consumption is less than the increase in income.
• The MPC is positive but less than one, so .
• A part of additional income is saved.
• The APC tends to fall as income rises because saving increases proportionately.

Mathematically:

This law explains why higher-income households generally save a larger proportion of their income than lower-income households.

Consumption is influenced by both economic and non-economic factors. Important determinants include:

• Disposable income: Higher disposable income generally increases consumption.
• Distribution of income: Greater inequality may reduce total consumption because rich households have a lower MPC than poor households.
• Wealth: An increase in wealth, such as property or financial assets, may encourage higher consumption.
• Interest rate: Lower interest rates can encourage borrowing and spending.
• Expectations: Expectations of higher future income increase present consumption, while fear of unemployment may reduce it.
• Price level: Rising prices reduce the purchasing power of income and may lower real consumption.
• Consumer credit: Easy availability of credit encourages expenditure on durable goods.
• Taxes: Higher taxes reduce disposable income and consumption.
• Social and cultural factors: Customs, habits, status, and family size also influence consumption decisions.

Autonomous consumption is the minimum level of consumption that takes place even when current income is zero. It may be financed through past savings, borrowing, or government assistance. It is represented by in the equation .

Induced consumption is the portion of consumption that changes with changes in disposable income. It is represented by .

Therefore, total consumption is the sum of autonomous and induced consumption.

National income is divided between consumption and saving. Therefore:

Suppose the consumption function is:

Substituting this into the income allocation identity:

Thus, the saving function is:

Here:

• represents dissaving when income is zero.
• is the marginal propensity to save (MPS).
• .

Since income is either consumed or saved:

Disposable income is allocated between consumption and saving:

Dividing both sides by gives:

Therefore:

where:

• is the average propensity to consume.
• is the average propensity to save.

Similarly, for changes in income:

If consumption is greater than income, saving is negative and dissaving occurs. If consumption is equal to income, saving is zero. If consumption is less than income, positive saving occurs.

Investment refers to expenditure on capital goods that increase the productive capacity of an economy. It includes spending on machinery, factories, equipment, inventories, infrastructure, and residential construction.

Investment is important because:

• It increases the stock of capital in the economy.
• It raises production and employment.
• It introduces new technology and improves productivity.
• It expands business capacity.
• It creates income through the multiplier process.
• It promotes long-term economic growth.
• It can improve living standards by increasing the availability of goods and services.

Investment is therefore both a component of aggregate demand in the short run and a source of productive capacity in the long run.

Gross investment is the total expenditure on new capital goods during a given period. It includes expenditure required to replace worn-out or depreciated capital.

Net investment is the addition to the capital stock after deducting depreciation.

The relationship is:

If gross investment equals depreciation, net investment is zero. If gross investment is less than depreciation, net investment is negative.

Investment can be classified in several ways:

• Fixed investment: Expenditure on durable capital goods such as machinery, buildings, tools, and equipment.
• Inventory investment: Changes in stocks of raw materials, semi-finished goods, and finished goods.
• Residential investment: Expenditure on the construction of houses and other residential structures.
• Replacement investment: Investment undertaken to replace worn-out or obsolete capital.
• Induced investment: Investment that changes with changes in income, demand, or output.
• Autonomous investment: Investment made independently of current income, often influenced by technological progress, population growth, or government policy.
• Public investment: Investment undertaken by the government in roads, schools, health facilities, and infrastructure.
• Private investment: Investment undertaken by individuals and private firms for profit.

The marginal efficiency of capital (MEC) is the expected rate of return from an additional unit of capital over its lifetime. It compares the expected future returns from a capital asset with its supply price.

A firm invests when the expected return on capital is greater than or equal to the cost of borrowing or the market interest rate. Investment is likely to occur when:

where is the interest rate.

The MEC is influenced by:

• Expected future demand
• Expected profits
• Cost of capital goods
• Technological improvements
• Business confidence
• Tax policies

Investment demand generally falls as the interest rate rises because borrowing becomes more expensive. Thus, the investment function is often written as:

where is autonomous investment and measures the sensitivity of investment to the interest rate.

The main determinants of investment are:

• Interest rate: A lower interest rate reduces borrowing costs and encourages investment.
• Expected rate of return: Firms invest when expected profitability is high.
• Demand conditions: Growing demand and sales encourage firms to expand capacity.
• Business expectations: Optimistic expectations increase investment, while uncertainty discourages it.
• Cost of capital goods: Lower prices of machinery and equipment make investment more attractive.
• Technological progress: New technology may require firms to purchase modern equipment.
• Government policy: Tax incentives, subsidies, regulations, and public infrastructure affect investment.
• Availability of finance: Easy access to bank loans and capital markets promotes investment.
• Level of existing capacity: Firms invest more when current productive capacity is insufficient.
• Political and economic stability: Stable conditions reduce risk and encourage long-term investment.

Autonomous investment does not directly depend on the current level of income or output. It is undertaken because of technological progress, population growth, government development programs, or basic infrastructure needs.

Induced investment changes in response to changes in income, output, demand, or profits. When sales increase, firms may expand their productive capacity and undertake additional investment.

Both forms contribute to aggregate demand and economic growth, but induced investment is more closely related to business conditions.

The investment multiplier shows the total increase in income resulting from an initial increase in investment. An increase in investment creates income for producers and workers. A portion of this income is spent again, creating further income and expenditure.

The investment multiplier is:

Under a simple model:

For example, if , then:

An increase in investment of would therefore increase total income by , assuming other factors remain constant.

The multiplier is significant because it explains how investment can generate a larger increase in national income, employment, and output.

Consumption contributes to economic growth through several channels:

• Creates aggregate demand: Household spending forms a major part of total demand for goods and services.
• Encourages production: Rising consumption encourages firms to increase output.
• Generates employment: Higher production requires more workers.
• Raises business revenue: Increased sales improve business profitability.
• Stimulates investment: Firms invest in additional capacity when demand is strong.
• Promotes the multiplier effect: One person's consumption becomes another person's income, creating successive rounds of spending.
• Improves living standards: Consumption provides households with goods and services that satisfy their wants.

However, excessive consumption financed by borrowing may create inflation, debt, and external imbalances. Sustainable growth requires a suitable balance between consumption and saving.

Investment is a key determinant of economic growth and business expansion because it increases both current demand and future productive capacity.

Its roles include:

• Capacity expansion: New machinery, factories, and equipment enable firms to produce more.
• Productivity improvement: Modern capital goods reduce costs and increase output per worker.
• Technological development: Investment supports research, innovation, and the adoption of advanced technology.
• Employment generation: New projects create direct and indirect employment.
• Income creation: Investment expenditure generates income through the multiplier process.
• Market expansion: Increased capacity allows firms to serve new markets and increase sales.
• Improved competitiveness: Efficient capital helps firms compete through better quality and lower costs.
• Infrastructure development: Public investment reduces business costs and supports private-sector growth.

Therefore, continuous investment is essential for long-term expansion and structural transformation.

In a simple closed economy without government and foreign trade, aggregate demand is the sum of consumption and investment:

Consumption represents household expenditure on goods and services, while investment represents business expenditure on capital goods and inventory accumulation.

The relationship works as follows:

• Higher income generally increases consumption.
• Higher consumption increases demand for business products.
• Strong demand and expected profits encourage investment.
• Investment creates income, which further increases consumption.
• The combined increase in consumption and investment raises aggregate demand and output.

In an open economy with government, the identity becomes:

where is government expenditure, is exports, and is imports. Consumption and investment are therefore central components of short-run economic activity.

The paradox of thrift states that an attempt by all households to save more may reduce total saving and national income in the short run.

The process is:

• Households decide to reduce consumption and increase saving.
• Aggregate demand falls because consumption is a major component of demand.
• Firms reduce production and employment.
• Household incomes decline.
• Lower income may reduce the actual amount of saving despite the desire to save more.

This can be expressed through the income identity:

If consumption falls while investment remains unchanged, equilibrium income falls through the multiplier process. The paradox is mainly a short-run result. In the long run, saving can be beneficial because it provides funds for investment, capital formation, and economic growth.

In a simple economy, equilibrium occurs when planned expenditure equals income:

Assume the consumption function is:

and investment is autonomous:

Substituting these functions into the equilibrium condition:

Rearranging:

Therefore:

This shows that equilibrium income depends on autonomous consumption, autonomous investment, and the MPC. A higher MPC increases the multiplier and produces a larger equilibrium level of income.

Interest rates influence investment because they determine the cost of borrowing and the opportunity cost of using funds.

• When interest rates fall, loans become cheaper.
• Lower borrowing costs increase the number of profitable investment projects.
• Firms purchase more machinery, construct new plants, and expand operations.
• Investment increases aggregate demand and employment.
• Higher income generated by investment may further increase consumption.

When interest rates rise, borrowing becomes expensive. Firms may postpone or cancel investment projects, especially those with low expected returns. Consequently, aggregate demand, output, and employment may decline.

A simple investment function can be written as:

where is autonomous investment, is the interest rate, and measures the responsiveness of investment to interest-rate changes. The actual response also depends on business confidence and expected profitability.