Risk
Diversification Explained: How Much Is Enough and Why It Works
Owning many things is not the same as being spread out. How correlation decides what really protects a portfolio, with worked numbers, a Helsinki angle and a check you can run today.
Diversification means spreading your money across holdings that do not all fall for the same reason, so a single bad event cannot sink the whole portfolio. What matters is not how many things you own but how differently they behave. Three forest companies are one bet; a mix of unrelated businesses, countries and asset types is a portfolio. Here is how to tell the two apart, with numbers.
In short
- Diversification limits the damage from any one company, sector or country, not from the whole market.
- The key is correlation: how often your holdings move together. Low correlation protects; high correlation only looks safe.
- Most company-specific risk fades with a few dozen well-spread shares, or with one broad index fund.
- Helsinki blue chips alone tie you to a handful of industries and one small economy.
What is diversification in investing?
The proverb about eggs and baskets covers half of the idea. The other half: the baskets should not all sit on the same shelf. In 1952 Harry Markowitz turned this into theory. The risk of a portfolio depends less on each holding than on how the holdings move together.
Every share carries two kinds of risk. One belongs to the company: a failed product, a lost contract, an accounting scandal. The other belongs to the market: a recession, a rate shock, a crisis that drags everything down at once. Spread across enough different companies, the first kind of disaster becomes a bad week rather than a ruined year. Against the second, diversification does little.
Correlation without the jargon
Correlation describes how often two things move in the same direction at the same time. It runs from +1 (always together) through 0 (no link) to -1 (always opposite). You need the intuition, not the formula.
Picture an ice-cream kiosk and an umbrella shop on the same Helsinki street. A wet summer hurts one and helps the other. Own both and the weather stops deciding your income. Own two ice-cream kiosks and a rainy July hits you twice.
Shares work the same way. Companies that share an industry, a raw material or a currency tend to rise and fall together. Finnish paper, pulp, packaging and timber businesses all ride the same forest-industry cycle. Three of them feel like three holdings. When pulp prices slump, they behave like one.
The single-event test
For any two holdings, ask: what one piece of news would hurt both? If the answer comes in seconds, they are more correlated than they look. And correlations are not fixed: in a sharp sell-off they rise, and for a while almost everything falls together. Diversification softens a crash; it does not cancel it.
Worked examples: diversification in numbers
One company against five
Put 10,000 euros into a single company and it falls 40%: you lose 4,000 euros. Split the same money into five holdings of 2,000 euros each. The same company falls 40% and the other four stay flat: you lose 800 euros, which is 8% of the portfolio.
False diversification against the real thing
Now put 9,000 euros into three forest-industry companies, 3,000 each. Pulp prices slump and all three fall 20%: you lose 1,800 euros, or 20% of the portfolio. Spread the same money across a forest company, a utility and a healthcare company instead. The forest company falls 20% (minus 600 euros), the utility gains 2% (plus 60), the healthcare company slips 5% (minus 150). Total loss: 690 euros, about 7.7%. Same event, well under half the damage.
The price you pay
Diversification also caps the upside. If one of five 2,000-euro holdings doubles, the portfolio gains 20%, not 100%. You give up the dream of one perfect pick in exchange for not depending on it.
| Layer | What it spreads | Example for a Finnish investor | Common trap |
|---|---|---|---|
| Companies | Single-company risk | Several Helsinki-listed firms instead of one | Many names, one industry |
| Sectors | Industry cycles | Forest, banking, technology, healthcare, utilities | Different labels, same raw material or customer |
| Countries and currencies | One economy, one currency | A global fund next to a Finnish core | A "global" fund that leans heavily on one market |
| Asset classes | Stock market risk | Shares plus bonds or savings | Riskier bonds that behave much like shares |
| Time | Bad entry points | A monthly fund savings plan | Stopping the plan after a bad month |
How much diversification is enough?
There is no magic number, but research gives a range. In 1968 John Evans and Stephen Archer found most of the benefit arrived within about ten randomly chosen shares. In 1987 Meir Statman argued for a few dozen. Both agree on the shape: each extra holding helps less than the last, and market risk never disappears.
- Individual shares: a couple of dozen, spread across industries and ideally countries, begins to do the job.
- Broad index funds: one purchase can hold hundreds or thousands of companies, one reason monthly fund saving through a bank is such a common start in Finland.
- A handful of blue chips: five familiar Helsinki names protect you against one company failing, not against a hard year for Finnish industry.
Then there is home bias: investors everywhere hold far more of their own country than its weight in the world, as Kenneth French and James Poterba showed in 1991. Finland is a small slice of global market value, so an all-Finnish portfolio is a concentrated bet, however familiar the names. Many Finns start with a few local shares in an equity savings account (osakesäästötili). A fine first step, as long as you know what it leaves unspread. The Financial Supervisory Authority (FIN-FSA) lists authorised firms.
Put the single-event test to work. In WallThrone, build a small book of WSX companies with your 25,000 play dollars and, before each new buy, ask which headline would hit it and what you already own. Then let Ticker TV give its answer.
Build a spread portfolioFalse diversification: when a portfolio only looks spread
The common mistake is owning many things that are secretly one thing.
- Several funds, same holdings. Three Nordic equity funds can share most of their top ten: three sets of fees for roughly one portfolio.
- One industry in disguise. A paper maker, a packaging group and a sawmill operator depend on the same wood and the same demand.
- Your salary and your shares. A large stake in your own employer ties income and savings to one company.
- One currency, one economy. Ten Finnish shares spread company risk but leave you exposed to the Finnish and euro-area cycle.
Finland has a famous lesson here. Around the turn of the millennium, Nokia alone made up a very large share of the Helsinki exchange's total value. Investors who thought they owned "the Finnish market" largely owned one phone maker, and felt it when that share price fell steeply in the following years. For how fast one headline can move a group of related shares, see how news moves stock prices.
How to check your own diversification in six steps
- List every holding: shares, funds, savings you invest yourself, and any employer shares or options.
- Open each fund's factsheet or key information document and note its top ten holdings and country split.
- Group everything by what drives it: industry, main customer, raw material, currency.
- Run the single-event test on your largest groups. One headline that would hit half the portfolio is a warning.
- Stress your biggest position. If it is 25% of the portfolio and halves, the total falls 12.5% from that alone.
- Write down a target mix and rebalance now and then, not every week, because every trade has a price. Here is what trading fees and commissions really cost.
Practising diversification with play money
Reading about correlation is useful; watching it is better. In WallThrone every player trades on the same fictional exchange, the WSX, where prices move every five seconds and Ticker TV news can shift them without warning. Hold one company for a while, then spread the same play money across five and compare how each version takes the headlines. And since what big players buy moves the price for everyone, a crowded position can turn faster than any chart suggests.
Keep the limits in view. The companies are fictional and prices come from the game's own model, so the patterns are not those of Nasdaq Helsinki. What carries over is the habit of asking what each new position adds. Costs count too: at a 0.05% commission, five buys of 5,000 play dollars cost 2.50 dollars each, 12.50 in total.
Frequently asked questions
Is one index fund enough diversification?
A broad index fund removes most company-specific risk in one purchase, which is why many beginners start there. It does not remove market risk, and a fund tracking one country or one sector is still concentrated. A Finland-only index is narrow; a global one is far broader. Check the top holdings and country split in its key information document.
How many stocks do you need to be diversified?
Research gives a range, not a rule. Early studies found most of the benefit within about ten randomly chosen shares; later work argued for a few dozen. Spread matters more than count: twenty shares in one industry are less diversified than ten across different industries and countries.
Is it enough to invest only in Finnish shares?
Helsinki-listed companies spread single-company risk but stay tied to a few dominant industries, the Finnish economy and the euro area. Many investors add international funds for breadth. What suits you depends on your goals and situation; the Financial Supervisory Authority (FIN-FSA) publishes consumer information and lists the firms it authorises.
Does diversification protect you in a stock market crash?
Only partly. In a sharp crash most shares fall together, because correlations rise when fear takes over. A diversified portfolio avoids the permanent damage of one company collapsing, but it still falls. What softens a market-wide drop is mixing asset classes, such as bonds and cash, not simply owning more shares.
WallThrone is a game with play money and fictional companies; it is not a broker and offers no access to real markets. This article is educational and is not financial advice.