Economic bubble

An economic bubble is a situation in which the market prices of assets rise substantially above levels that can be justified by underlying economic fundamentals, often accompanied by expectations of further price increases.

A bubble can occur in financial assets, real estate, commodities, or other markets.

A simplified representation is:

$\text{Rising Asset Prices}\to \text{Higher Expectations}\to \text{Increased Demand}\to \text{Further Price Increases}$

This feedback mechanism can produce a self-reinforcing increase in asset prices.

Bubble formation

Economic bubbles can develop when rising prices attract additional buyers who expect prices to continue increasing.

A simplified mechanism is:

$\text{Initial Price Increase}\to \text{Positive Expectations}\to \text{Increased Demand}\to \text{Further Price Increase}$

The process can be reinforced by factors such as abundant liquidity, credit expansion, speculation, leverage, technological or economic developments, and expectations of continued appreciation.

A simplified representation is:

$\text{Liquidity}+\text{Credit}+\text{Speculation}+\text{Positive Expectations}\to \text{Asset-Price Appreciation}$

These factors do not necessarily produce a bubble individually.

Fundamental value

A commonly used approach to identifying a potential bubble is to compare market prices with estimates of fundamental value.

For financial assets, fundamental value can be related to expected future cash flows.

A simplified representation is:

$\text{Asset Price}\approx \text{Present Value of Expected Future Cash Flows}$

For an asset generating cash flows $C{F}_t$, a simplified present-value relationship is:

$P=\sum _{t=1}^n\frac{C{F}_t}{(1+r{)}^t}$

where:

• $P$ = present value of the asset;
• $C{F}_t$ = expected cash flow in period $t$;
• $r$ = discount rate;
• $n$ = number of periods.

A substantial divergence between market prices and reasonable estimates of fundamental value may indicate overvaluation, although valuation alone does not establish the existence of a bubble.

Speculation

Speculation can contribute to the formation of an economic bubble when investors purchase assets primarily because they expect to sell them later at higher prices.

A simplified mechanism is:

$\text{Expected Price Appreciation}\to \text{Speculative Demand}\to \text{Higher Asset Prices}\to \text{Higher Expected Appreciation}$

Speculative activity occurs in many markets and does not necessarily imply that a bubble exists.

Leverage and credit

Financial leverage and credit expansion can amplify both the formation and collapse of asset-price bubbles.

A simplified mechanism is:

$\text{Credit Expansion}\to \text{Higher Purchasing Capacity}\to \text{Increased Asset Demand}\to \text{Higher Asset Prices}$

Rising asset prices can also increase the value of collateral, potentially supporting additional borrowing.

$\text{Higher Asset Prices}\to \text{Higher Collateral Values}\to \text{Greater Borrowing Capacity}\to \text{Additional Asset Purchases}$

The reverse process can occur when asset prices decline.

$\text{Falling Asset Prices}\to \text{Lower Collateral Values}\to \text{Deleveraging}\to \text{Asset Sales}\to \text{Further Price Declines}$

Bubble peak and reversal

A bubble can reach a point at which expectations of continued price appreciation weaken.

Potential triggers for a reversal include:

• changes in interest rates;
• tightening credit conditions;
• deterioration in economic fundamentals;
• regulatory changes;
• negative economic news;
• declining investor confidence;
• reduced liquidity;
• realization that valuations have become difficult to justify.

A simplified reversal mechanism is:

$\text{Negative Shock}\to \text{Falling Expectations}\to \text{Reduced Demand}\to \text{Falling Prices}$

Bubble collapse

A rapid and substantial decline in asset prices following a period of excessive appreciation is sometimes described as a bubble burst or bubble collapse.

A simplified mechanism is:

$\text{Price Decline}\to \text{Loss of Confidence}\to \text{Selling}\to \text{Further Price Decline}$

When leveraged investors are involved, margin calls and forced selling can amplify the decline.

$\text{Price Decline}\to \text{Margin Pressure}\to \text{Forced Selling}\to \text{Further Price Decline}$

Economic effects

The consequences of an economic bubble can extend beyond the asset market in which the bubble developed.

Potential effects include:

• losses for investors;
• deterioration in household or corporate balance sheets;
• reduced consumption;
• reduced investment;
• financial-sector stress;
• increased defaults;
• tighter credit conditions;
• unemployment;
• broader economic contraction.

A simplified transmission mechanism is:

$\text{Asset-Price Collapse}\to \text{Wealth Loss}\to \text{Reduced Spending}\to \text{Lower Economic Activity}$

The economic effects depend on the size of the asset market, the degree of leverage, the exposure of financial institutions, and the importance of the affected assets to the broader economy.

Bubble indicators

Analysts may consider multiple indicators when assessing whether an asset market exhibits bubble-like characteristics.

Potential indicators include:

• unusually high valuation multiples;
• rapid price appreciation;
• high trading activity;
• extreme investor sentiment;
• rapid credit growth;
• increasing leverage;
• substantial divergence between prices and earnings;
• speculative concentration;
• unusually high expectations of future price appreciation.

A simplified conceptual framework is:

$\text{Bubble Risk}=f(\text{Valuation},\text{Leverage},\text{Liquidity},\text{Sentiment},\text{Price Momentum})$

This expression is conceptual rather than a standardized statistical formula.

Historical examples

Economic bubbles have occurred in different asset markets and historical periods.

Frequently discussed examples include:

• the Dutch tulip mania;
• the South Sea Bubble;
• the Dot-com bubble;
• the United States housing bubble;
• the Japanese asset price bubble.

The characteristics, causes, and economic consequences of these episodes differ substantially.

Identification and debate

Identifying an economic bubble in real time is difficult because the fundamental value of an asset is often uncertain.

An asset that appears substantially overvalued according to one valuation model may be justified under different assumptions concerning future growth, interest rates, risk, or cash flows.

Consequently, the existence of a bubble is often easier to establish retrospectively than during the period of rapid price appreciation.

A simplified distinction is:

$\text{High Valuation}\equiv ̸\text{Economic Bubble}$

Similarly:

$\text{Rapid Price Increase}\equiv ̸\text{Economic Bubble}$

Bubble analysis therefore generally considers valuation, expectations, credit conditions, leverage, market behavior, and underlying economic fundamentals together.

See also

• Asset bubble
• Financial bubble
• Speculation
• Financial leverage
• Credit cycle
• Financial cycle
• Deleveraging
• Debt deflation
• Financial crisis
• Market psychology