Diversification in Practice
You've spread your money across five different tech stocks and feel well diversified. Whether that's true doesn't depend on how many stocks are in the portfolio, but on how independent they actually are from each other.
You're convinced that technology and AI will define the future, and built your portfolio around that: five different large tech stocks, each weighted roughly equally. No index fund, no ETFs, just individual stocks from the same sector. Because it's five different companies, it feels like you're sufficiently diversified.
That feeling is misleading. Diversification doesn't mean holding several positions — it means holding positions that don't move in the same direction at the same time when a shared trigger hits. Five tech stocks tend to react very similarly to the same events: rising interest rates, new regulation for the sector, or a disappointing outlook from one major competitor can put pressure on all five stocks at once.
The portfolio is therefore less diversified than the number of positions suggests. At its core it carries one big risk — the tech sector as a whole — just spread across five labels.
Genuine diversification only happens when positions from different sectors, regions, and ideally different asset classes are combined, so that a single event doesn't hit the entire portfolio at the same time.
The key measure of how strongly two investments move together is correlation. At a correlation near +1, two prices move almost in lockstep; near 0, largely independently; at negative correlation, they tend to move in opposite directions. Stocks from the same sector historically tend to show clearly positive correlation to each other, because they react to the same sector-specific news, interest rate changes, and business cycles.
That significantly reduces the diversification benefit of an additional position within the same sector: statistically, a portfolio's overall risk drops meaningfully mainly when new positions have low or even negative correlation to the existing ones — not simply because the number of positions increases.
In practice, a rough check is to ask: what single event could significantly hit every position in the portfolio at the same time? If such an event is easy to identify — say, new regulation for an entire sector — that's a sign of insufficient diversification, regardless of how many individual positions are held.
Summary
- The number of stocks in a portfolio says nothing about genuine diversification.
- Stocks from the same sector often move together when a shared trigger hits.
- Real diversification needs different sectors, regions, and asset classes.
Did you get it?
Why isn't owning five different stocks automatically diversification?
Because the number of positions says nothing about how spread out they are. What matters is how strongly the prices move together, not how many names are in the portfolio.
What does high correlation between stocks mean?
That their prices mostly move in the same direction — a shared trigger tends to make them fall or rise at the same time.
How can you tell if a portfolio is genuinely diversified?
By whether it combines different sectors, regions, and asset classes that aren't hit by the same events at the same time.
What would you do?
Related
- DiversificationStage 1
- CorrelationStage 2
- Asset Classes ComparedStage 0