A Broader Stock Market Rally Can Still Hide Concentrated Risk

The recent stock-market advance appears healthier than the rally that preceded it. Gains are no longer confined to a small group of technology companies, while industrial, healthcare, transport and energy shares have taken a more prominent role. In Germany, companies such as Airbus, Bayer, Siemens Energy and DHL have helped drive the DAX higher even as former favourites including SAP and Rheinmetall have fallen sharply from their peaks.

A larger number of rising shares usually improves the foundations of a bull market. It reduces the index’s dependence on a few exceptional performers and suggests that investors are finding opportunities across more of the economy. Yet broader participation does not necessarily mean that portfolios have become genuinely diversified.

Companies from different sectors can still depend on the same economic assumptions. Several funds can contain many of the same largest holdings. An investor who owns European, global and technology exchange-traded funds may appear diversified while remaining heavily exposed to US equities, the dollar and a narrow group of dominant companies.

Market breadth is therefore useful, but it should not be mistaken for a complete measure of risk.

More Winners Do Not Automatically Create a Safer Market

A narrow rally is relatively easy to recognise. A small number of companies account for most index gains, valuations rise far above the rest of the market and investor sentiment becomes concentrated around one compelling theme.

A broadening rally looks more reassuring. Previously overlooked sectors begin to rise, smaller companies participate and earnings growth appears to extend beyond the original market leaders. This can signal that economic conditions are improving and that the advance has developed a stronger base.

It can also reflect a rotation rather than a reduction in risk.

When highly valued technology shares lose momentum, capital often moves towards industries that have lagged behind. Banks, industrial companies, healthcare groups or consumer businesses may rise because investors expect them to catch up, not because their underlying prospects have changed substantially. Lower starting valuations can support this process, but the breadth of the move may conceal how strongly it still depends on favourable market liquidity and investor confidence.

A market in which ten sectors rise is broader than one driven by a handful of technology shares. It is not necessarily more resilient if all ten sectors are being supported by the same expectations of falling interest rates, strong economic growth and uninterrupted corporate earnings.

The distinction matters because those assumptions can reverse together.

Different Sectors May Share the Same Economic Bet

Sector labels create a convenient impression of diversification. A portfolio containing technology, industrial, financial, healthcare and consumer shares appears to spread risk across several parts of the economy.

In practice, companies in different industries may react to the same underlying forces. A lower interest-rate environment can support technology valuations, property companies, banks and highly indebted businesses at the same time. Strong capital expenditure may benefit semiconductor producers, industrial automation groups, engineering companies and electrical-equipment manufacturers. Government spending can lift defence, construction, infrastructure and energy businesses simultaneously.

These are separate sectors, but not necessarily separate investment theses.

The current enthusiasm for artificial intelligence provides a clear example. The immediate beneficiaries include semiconductor designers and cloud platforms, but the theme has expanded to data-centre equipment, electricity networks, cooling systems, construction, industrial property and power generation. An investor who owns companies across all these categories may believe the portfolio is diversified because the holdings carry different sector classifications. Their revenues and valuations may still depend on the continuation of the same AI investment cycle.

The same applies to defence spending, electrification and infrastructure renewal. Each theme reaches across multiple industries, creating clusters of companies whose share prices can move together despite appearing unrelated in a conventional portfolio overview.

Diversification should therefore be assessed by economic drivers as well as by sector.

Several ETFs Can Reproduce the Same Portfolio

Exchange-traded funds have made diversification inexpensive and accessible, but the number of funds in a portfolio says little about the number of independent risks it contains.

A global equity ETF, a US equity ETF and a technology ETF may hold many of the same large American companies. The global fund is likely to allocate heavily to the United States because most broad indices are weighted by market capitalisation. The US fund increases that exposure, while the technology fund concentrates it further.

Adding a European or sustainability-focused ETF does not always solve the problem. European indices may still contain multinational companies whose earnings depend heavily on US and Asian demand. Sustainability indices often exclude certain industries, increasing the weight of technology and other sectors that meet their selection criteria. The resulting portfolio may contain more funds but fewer distinct sources of return than expected.

Overlap is not inherently undesirable. An investor may deliberately want to emphasise certain companies or regions. The risk arises when duplication is accidental and the portfolio is assumed to be more balanced than it is.

Investors should examine the largest positions across all their funds, not only within each product. They should also calculate their combined exposure by country, currency, sector and investment theme.

A portfolio of five ETFs can still behave like one concentrated position when markets fall.

Market-Capitalisation Weighting Reinforces Past Success

Most major equity indices allocate more capital to companies with higher market values. As a share price rises, the company occupies a larger position in the index and in every fund that tracks it.

This structure is efficient and inexpensive, but it contains an important characteristic: investors automatically increase their exposure to companies after those companies have become more valuable.

During a long bull market, the effect can be considerable. Successful businesses grow into dominant index positions, attract further passive investment and exert increasing influence over overall returns. The index may contain hundreds or thousands of companies while its performance depends disproportionately on a relatively small group.

A broadening rally can reduce this concentration temporarily if other shares begin to outperform. It does not remove the structural effect of market-capitalisation weighting. The largest companies remain the largest holdings unless their relative market values fall significantly.

This is why the number of securities in an index can be misleading. An index containing 500 companies is not equivalent to a portfolio in which each company contributes equally. Its effective concentration may be much higher than the headline number suggests.

Equal-weighted indices offer one alternative, though they introduce different risks. They allocate more to smaller businesses, require more frequent rebalancing and may underperform when the largest companies continue to dominate. They should not be viewed as automatically superior, but they can help reveal how much of a conventional index’s return comes from its largest constituents.

Geographic Diversification Can Be Weaker Than It Appears

Investors often divide portfolios into US, European, Asian and emerging-market allocations. This is a useful starting point, but the location of a company’s stock-market listing does not necessarily show where its economic exposure lies.

A European industrial company may generate a large share of its revenue in the United States and China. An American technology group may depend on Asian manufacturing and global advertising expenditure. A Swiss consumer company may earn most of its income outside Switzerland.

Holding companies listed in different countries can therefore provide less geographic diversification than expected. A global slowdown, trade conflict or change in Chinese demand may affect businesses across several exchanges at once.

Currency exposure adds another layer. A fund may be denominated in euros while holding assets whose underlying earnings and valuations are tied to the US dollar. The trading currency of the fund does not remove the economic currency exposure of the companies inside it.

Investors should look at revenue sources, supply chains and currency sensitivity alongside the country printed on the fund label. This is particularly important for portfolios built through broad global indices, which may allocate a majority of their capital to the United States even when marketed as worldwide investments.

Global diversification remains valuable, but it must be measured rather than assumed.

Correlations Rise When Investors Need Diversification Most

Assets that behave differently during calm markets can become highly correlated during periods of stress. Investors sell what they can, risk appetite falls across regions and sectors, and companies with otherwise distinct business models decline together.

This does not make diversification ineffective. A well-constructed portfolio can still reduce losses and improve recovery over time. It does mean that historical correlations observed during normal conditions may underestimate the relationships that emerge during a crisis.

Equities are especially vulnerable to this effect because they share a common exposure to investor confidence, financing conditions and expectations for future profits. Defensive sectors may fall less than cyclical ones, but they are not guaranteed to rise when the broader market declines.

True diversification may therefore require assets with different economic functions, not simply different categories of shares. High-quality bonds, cash reserves, inflation-sensitive assets and selected alternative investments can provide exposures that are less dependent on corporate earnings.

The appropriate mix depends on the investor’s objectives, time horizon and tolerance for volatility. The relevant point is that a portfolio consisting entirely of equities remains an equity portfolio, regardless of how many regions or sectors it includes.

Earnings Expectations Can Concentrate Risk Quietly

Market concentration is often discussed through share prices and index weights, but expectations can create another form of common exposure.

A broad range of companies may be priced for strong earnings growth. Industrial groups may be expected to benefit from infrastructure investment, banks from resilient economies, consumer companies from rising household income and technology businesses from continued AI spending. The stories differ, but the valuations may all assume that economic growth remains supportive.

This creates vulnerability even when individual price-to-earnings ratios do not appear extreme. If analysts have raised profit forecasts across much of the market, disappointing economic data can affect many sectors at once.

Investors should therefore examine not only current valuations but also the assumptions embedded in them. A company trading at a moderate multiple may still be expensive if its expected earnings prove difficult to achieve.

Forecast revisions can be particularly informative. When share prices rise while earnings expectations remain stable, valuations are expanding. When both prices and forecast profits rise, the advance may have stronger fundamental support. Neither pattern provides certainty, but the distinction helps identify what is driving returns.

A broader rally supported by improving profits is generally more robust than one created mainly by investors paying higher prices for the same expected earnings.

Concentration Is Not Always a Reason to Sell

Some concentration is unavoidable. The strongest companies and largest economies naturally occupy meaningful positions in global markets. Reducing every large exposure mechanically can lead investors to sell successful businesses too early and replace them with weaker alternatives.

Concentrated portfolios can also deliver excellent returns when the underlying thesis is correct. The problem is not concentration itself but concentration that the investor has failed to recognise, assess or accept deliberately.

A portfolio heavily exposed to US technology may be appropriate for an investor with a long horizon, substantial risk capacity and strong conviction in the sector. The same portfolio may be unsuitable for someone approaching retirement who expects stable withdrawals and believes several overlapping ETFs have provided broad diversification.

The portfolio should match the investor’s financial circumstances rather than an abstract ideal of balance.

This is also why reacting to every warning about a possible bubble can be damaging. Markets can remain expensive for long periods, and record levels are a normal feature of growing equity markets. Selling solely because an index has reached a new high may leave investors outside the market during further gains.

A more useful response is to examine how the portfolio would behave if its dominant assumptions proved wrong.

A Practical Concentration Audit

Investors do not need a complex risk system to identify the most obvious weaknesses. A useful review begins by combining all holdings into one portfolio rather than evaluating each fund separately.

The first step is to identify the ten largest underlying companies. Investors are often surprised by how much these positions represent once duplicate holdings across funds are added together.

The same exercise should be repeated for countries, currencies and sectors. A global label can conceal a large US allocation, while several apparently distinct funds may create a substantial dollar exposure.

The portfolio should then be grouped by investment theme. Companies linked to AI infrastructure, defence expenditure, lower interest rates or Chinese demand may span several sectors. This thematic view often reveals concentrations that standard fund documents do not show clearly.

Finally, investors should consider a small number of adverse scenarios. What happens if interest rates remain high? What if AI capital expenditure slows? What if the dollar weakens? What if global manufacturing enters a downturn?

The objective is not to forecast which event will occur. It is to identify whether several holdings would respond to the same event in the same way.

Where the answer is yes, the investor can decide whether the exposure is intentional and appropriately sized.

Rebalancing Should Follow the Portfolio, Not the Headlines

A broader rally can be an opportunity to rebalance because gains outside the original market leaders may make it easier to adjust exposures without abandoning equities altogether.

Rebalancing does not require predicting the end of the bull market. It means restoring the portfolio to a planned allocation after market movements have changed its risk profile. An asset that performed exceptionally well may now represent a larger position than the investor intended, even when its long-term prospects remain attractive.

The process can involve directing new contributions towards underrepresented assets, trimming selected positions or replacing overlapping funds with a simpler structure. Tax consequences, transaction costs and the investor’s time horizon should all be considered.

Frequent changes are rarely necessary. A disciplined annual review or predetermined tolerance bands can prevent the portfolio from drifting while avoiding constant reactions to market news.

The purpose is not to eliminate volatility. Equity investors must accept that markets will decline periodically. Rebalancing aims to ensure that the losses they experience arise from risks they consciously chose rather than exposures hidden inside apparently diversified holdings.

Breadth Is Encouraging, but Portfolio Structure Matters More

The participation of more companies in a market advance is generally constructive. It suggests that investors are looking beyond a narrow group of dominant shares and that opportunities may be spreading across the economy.

It does not prove that valuations are sustainable, earnings expectations are realistic or individual portfolios are well diversified. Sector rotation can distribute gains while leaving the market dependent on the same interest-rate outlook, liquidity conditions and growth assumptions. Multiple funds can reproduce the same holdings, while geographic labels can obscure shared economic exposure.

Investors should welcome broader participation without drawing too much reassurance from it. The strength of a portfolio is determined less by how many securities it contains than by how many genuinely independent sources of risk and return it brings together.

A rally can broaden on the surface while remaining concentrated underneath. Recognising that distinction is more useful than trying to determine precisely when the next market correction will begin.