What is portfolio diversification?

Portfolio diversification is spreading a portfolio's assets or sources of risk across several objects, instead of letting the outcome depend mainly on one of them. It concerns not only "how many kinds of asset are held", but also how large a share each asset takes, and whether they would be affected by the same factor.

Diversification can change how much a single asset, issuer or system failure affects a whole portfolio, but it cannot guarantee a profit, and it does not remove risks such as a market decline, insufficient liquidity or an operational mistake. This article only explains how the concept works; it does not provide asset allocation proportions, token selection or personal investment advice.

Diversification reduces a portfolio's dependence on a single outcome

The larger the share an asset takes in a portfolio, the more its price changes can usually drive the portfolio's outcome. Putting every asset into the same object makes the portfolio's outcome depend entirely on that object; once holdings are spread across several objects, the effect any one asset produces also depends on its portfolio weight.

Spreading across several names, however, has not necessarily spread the risk. If ten assets all depend on the same industry, the same collateral or the same trading platform, they may still be affected by the same event at once. What diversification genuinely separates should be the sources of risk behind an outcome, not merely the number of assets in an interface.

Weight determines how much each asset can affect a portfolio

A portfolio weight is the proportion of a portfolio's total value that one asset's value represents. Suppose a portfolio contains three assets, one of which takes 90% while the other two take 5% each; even though the number of assets is three, most of the portfolio's movement is still determined by the first one.

Weights also shift with prices. If one asset rises faster than the others, its share of the portfolio increases; if it falls further, its share decreases. After a period of time, the actual weights may already differ from the proportions recorded at the outset.

Concentration is used to describe whether a portfolio is dominated by a few holdings. Besides looking at the largest holding and the combined weight of the largest few, you can also calculate an "effective number of assets": square each weight, add the squares together, then divide 1 by that total. This number is not the actual count of holdings; it converts unequal weights into the number of equally weighted assets that would carry the same concentration. MSCI's note on the effective number of assets shows how this measure reflects a weight distribution. It only reflects whether weights are concentrated, not asset correlation, liquidity or shared dependencies.

Correlation shows whether assets have often moved together in the past

Correlation uses a number between -1 and +1 to summarise the degree to which two assets' returns moved together over a historical period. Close to +1 indicates they often moved in the same direction; close to -1 indicates they often moved in opposite directions; close to 0 indicates no evident linear relationship in either direction.

When two assets do not always move at the same time and by the same magnitude, a rise or fall in one asset may partly offset the movement of the other. A portfolio's volatility therefore depends not only on each asset's own volatility, but also on how the assets move together. CFA Institute's note on portfolio risk lists asset weights, individual volatilities and correlation as factors that jointly determine portfolio risk.

Correlation is not a fixed property. A calculated result is affected by the chosen time range, the data frequency and the market phase; correlation having been low in the past does not mean it will stay low. Correlation also mainly describes linear co-movement, and cannot fully represent situations such as an extreme decline, a liquidity interruption or being unable to execute at all.

Two portfolios with the same number of assets can be diversified quite differently

When comparing two portfolios, you cannot simply count the holdings. The following four questions change the actual degree of diversification:

• whether weights are concentrated: when a few holdings take most of the value, the remaining holdings may have very little effect on the portfolio;
• whether sources of risk repeat: assets with different names may depend on the same market, industry, issuer, collateral or technical infrastructure;
• whether assets often move together: assets that have historically moved in the same direction to a high degree usually offset each other's volatility less;
• whether risk contribution is concentrated: an asset with a smaller weight but very high volatility may also contribute a larger proportion of a portfolio's volatility.

Risk contribution is the effect that one asset, together with how it moves with the other assets, has on a portfolio's overall volatility. It is not the same thing as a capital weight. Two assets each taking half the capital do not necessarily each contribute half the volatility.

Early portfolio research already distinguished "many assets" from "different sources of risk". Markowitz's paper "Portfolio Selection" uses the variance and covariance of asset returns to show that a portfolio's outcome depends not only on individual assets, but also on how the assets move together. Variance describes how dispersed one set of returns is around its mean; covariance describes whether two sets of returns tend to move together.

Crypto assets may share market and technical risk

Holding several digital assets does not necessarily create several independent sources of risk. Different tokens may be affected at the same time by crypto asset market sentiment, a change in liquidity or a failure of the same infrastructure. Academic research has also found that some common market factors can explain variation in the returns of several crypto assets; a "factor" here is a shared driver that can make several assets move together, rather than any one token itself. "Common Risk Factors in Cryptocurrency" offers one empirical analysis of this kind of co-movement.

A crypto asset portfolio may also share the following dependencies beyond price:

• several tokens deployed on the same blockchain, jointly depending on that network to process transactions;
• several assets entering another network through the same cross-chain bridge or custodial institution;
• several stablecoins or wrapped assets depending on the same issuer, reserve assets or redemption channel;
• several decentralized finance positions — that is, the contract records formed by operations such as borrowing, depositing or posting collateral — using the same kind of collateral or the same price data source;
• assets spread across several accounts, while the signing permissions or recovery credentials are controlled by the same person, device or service;
• several assets held on the same trading platform, jointly bearing that platform's access and custody risk.

These dependencies show that price diversification, protocol diversification, network diversification and custody diversification are not the same question. A portfolio can be very diversified in token names while being highly concentrated in its underlying network or in how the assets are kept.

Rebalancing moves shifted weights back into a predetermined range

Rebalancing is adjusting portfolio weights that have drifted back to proportions or ranges set in advance. Its purpose is to re-establish the original portfolio structure, not to predict which holding will rise next.

Price changes, inflows and outflows of funds, and returns generated by assets can all cause weights to drift. Rebalancing usually requires buying, selling or moving assets, so it may incur trading fees, spreads, onchain network fees and execution impact; some assets may also be hard to adjust to an intended proportion because of insufficient liquidity.

Rebalancing frequency and trigger ranges affect both cost and the degree of weight drift. CFA Institute's note on asset allocation likewise lists transaction costs, liquidity and weight constraints as limits in portfolio implementation. There is no fixed frequency that applies generally, apart from specific objectives, costs and asset conditions.

Diversification, hedging and decentralization are not the same thing

Diversification spreads dependence across several sources of risk; hedging instead uses another position or arrangement to offset one definite risk. A hedge may, for example, address an exchange rate or price change, but it brings new conditions of its own such as cost, term and counterparty. Diversification does not require every risk to have a trade in the opposite direction.

Diversification also differs from decentralization in blockchains. Decentralization concerns whether a network's validation, governance or system control is concentrated in the hands of a few participants; portfolio diversification concerns how capital weights and sources of risk are distributed. A decentralized network's token can take a very high share of one portfolio, and an asset issued by a centralized institution can be only a small part of a portfolio.

Diversification cannot remove joint declines or risks outside a portfolio

Diversification can only address certain problems of risk distribution; it will not make a portfolio "safe". It has several important limits:

• when markets decline generally, several assets may lose value at the same time;
• historical correlation may change under market stress, and assets that were previously out of step begin to move in the same direction;
• different assets may conceal a dependence on the same issuer, collateral, platform or network;
• when liquidity falls, weights and prices on paper may not be realizable through actual trades;
• increasing the number of assets adds complexity in record-keeping, safekeeping, fees and operations;
• when a data sample is too short or an asset's history is limited, correlation and volatility estimates may be unstable;
• diversification will not remove fraud, private key exposure, contract defects or a custodian's failure.

Diversification may also mean a portfolio captures only part of a large rise in one asset. It changes the way different outcomes affect a portfolio, but does not judge in advance which outcome is better.

Judging the degree of diversification means looking at holdings and shared dependencies together

When describing a portfolio's degree of diversification, you can examine the following information in turn, rather than arriving directly at a "diversified" or "not diversified" conclusion:

1. which assets the portfolio contains, and what each one's actual weight is;
2. how much of the portfolio's value the largest holding and the largest few holdings take;
3. whether the assets' price changes have long been driven by similar factors;
4. which assets depend on the same issuer, network, collateral, platform or custody arrangement;
5. whether the assets' contributions to overall volatility are concentrated;
6. whether weights will be readjusted under some established set of rules once they shift;
7. whether trading fees, liquidity and operational limits would impede an actual adjustment.

This information answers questions about a portfolio's structure; it does not automatically establish that a portfolio suits a particular person. Personal objectives, financial circumstances and capacity to bear losses belong to a separate suitability judgement, which cannot be settled by a degree of diversification alone.

FAQ

Does holding more coins mean a higher degree of diversification?

Not necessarily. Several tokens may move in the same direction to a high degree, and may jointly depend on the same network, collateral, cross-chain bridge, platform or custody service. You also have to look at weights, correlation and underlying dependencies.

Does low correlation mean low risk?

No. Low correlation only indicates that two assets did not often move in the same direction within the chosen historical sample. One asset may still be highly volatile, short of liquidity or subject to an independent failure, and correlation changes over time.

Is an equally weighted portfolio necessarily more diversified than a market-cap weighted one?

Not necessarily. Equal weighting can reduce concentration of capital weights, but the assets may still be exposed to the same sources of risk; a market-cap weighted portfolio may instead be concentrated because a few large-cap holdings take a higher share. The two also produce different trading, liquidity and rebalancing conditions.

Can diversification avoid losses?

No. Diversification will not stop a whole market from declining, and it does not remove risk from the assets themselves, a platform, a network, liquidity or operations.

Is putting assets in several wallets diversification?

This may separate some device or account risk, but if all the wallets share the same recovery credential, are controlled by the same service, or sit on the same compromised device, the critical dependency remains concentrated. The number of wallets and the degree of diversification of asset price risk are also two different questions.

Related concepts

Continue with digital asset, stablecoin, crypto token and crypto custody, or return to the Crypto Glossary.

Sources

• Harry Markowitz: "Portfolio Selection" — the foundational study explaining portfolio return and volatility through asset weights, variance and covariance.
• CFA Institute: Portfolio Risk and Return — Part I — the relationship between portfolio weights, asset volatility, correlation and portfolio risk.
• CFA Institute: Principles of Asset Allocation — implementation limits such as weight constraints, rebalancing, transaction costs and liquidity.
• MSCI: How Concentrated Are Small Caps Today? — a worked example of the effective number of assets and weight concentration.
• The Journal of Finance: Common Risk Factors in Cryptocurrency — empirical research on common market, size and momentum factors in crypto assets.