Diversification is the practice of spreading investments across many different assets so that the failure of any one investment does not devastate your portfolio. It is the closest thing to a free lunch in investing — reducing risk without necessarily reducing expected returns.
Why Diversification Matters
The risk of owning a single investment is obvious: if that company fails, you lose everything invested in it. Diversification means the poor performance of any one holding has a limited impact on your total portfolio.
Example: A portfolio of 20 equally-weighted shares — if one company goes to zero, you lose 5% of your total portfolio. If you owned only that one share, you lose 100%.
Beyond single-company failure, diversification also smooths out the inevitable outperformance and underperformance of different sectors, countries, and asset classes over time.
The Three Levels of Diversification
Level 1 — Asset class diversification
Spread across fundamentally different types of assets:
- Shares (high growth, high volatility)
- Bonds (lower growth, lower volatility, different return drivers)
- Cash (capital stable, low return)
- Property (income, inflation sensitivity)
Different asset classes tend to perform differently in different economic environments — not always, but over time, this reduces portfolio volatility.
Level 2 — Geographic diversification
Don’t concentrate in one country:
- Australian shares: 2% of global market cap, heavy in banks and resources
- US shares: 65% of global market cap, strong in technology and healthcare
- European shares: financials, industrials, consumer brands
- Asian shares: manufacturing, technology, consumer growth
A portfolio of only Australian shares is heavily concentrated in one small slice of the global economy. Adding global ETFs (VGS, IWLD) broadens exposure dramatically.
Level 3 — Sector/stock diversification within each market
Even within Australian shares, concentration risks exist:
- The ASX is dominated by financials (30%+) and materials (25%+)
- Healthcare, technology, and consumer discretionary are underrepresented vs global markets
- Top 10 ASX stocks represent ~40% of the S&P/ASX 200
Broad-market ETFs (VAS, A200) automatically diversify across all ASX sectors.
How ETFs Make Diversification Easy
A single ETF purchase can provide instant exposure to hundreds or thousands of companies:
| ETF | Holdings | Diversification provided |
|---|---|---|
| VAS (Vanguard Aus Shares) | ~300 ASX stocks | Full Australian market coverage |
| VGS (Vanguard International) | ~1,500 global stocks | 23 developed markets |
| VDHG (Vanguard Diversified High Growth) | 7,000+ global securities | Shares, bonds, multiple markets — one ETF |
| VGE (Vanguard Emerging Markets) | ~1,000 EM stocks | China, India, Brazil, Taiwan |
Two ETFs — VAS + VGS — provide exposure to approximately 1,800 companies across Australia and global developed markets, covering most diversification needs for the growth portion of a portfolio.
The Concentration Risk in Australian Super
Many Australians’ super funds are heavily weighted toward Australian shares (20–30% of the total portfolio in ASX stocks) — which represents a significant home-country bias given Australia is 2% of world markets. Some super funds have addressed this with increased international allocations; others remain heavily domestic.
Check your super fund’s investment option statement to understand how your super is actually allocated.
Over-Diversification
There is a point of diminishing returns. Owning 15 different ETFs that all track similar global share indices doesn’t meaningfully reduce risk compared to 3–4. Over-diversification:
- Increases complexity
- May increase total fees (especially if multiple funds have overlapping holdings)
- Doesn’t meaningfully reduce risk beyond what 3–5 well-chosen ETFs provide
Most Australians are well-served by 3–5 ETFs covering: Australian shares, international developed markets, and one defensive asset (bonds or cash).
Correlation — Why Asset Classes Diversify Each Other
Diversification works because asset classes don’t always move together. Correlation ranges from +1 (move identically) to -1 (move opposite):
| Asset pair | Typical correlation |
|---|---|
| Australian shares ↔ International shares | ~0.70 (fairly correlated) |
| Shares ↔ Government bonds | ~−0.20 to +0.20 (low/negative) |
| Shares ↔ Cash | ~0.00 (uncorrelated) |
| Shares ↔ Gold | ~0.00 to +0.10 |
Bonds and shares have historically been low or negatively correlated — which is why adding bonds to a share portfolio reduces volatility without proportionally reducing returns.
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Frequently Asked Questions
How many stocks do you need to be diversified in Australia? Research suggests 20–30 randomly selected stocks eliminate most individual stock risk in a portfolio. However, for most investors, broad market ETFs (VAS holds ~300 ASX stocks) provide far better diversification than selecting individual stocks — plus lower transaction costs and no stock-picking required.
Is VAS a diversified investment? VAS (Vanguard Australian Shares ETF) provides diversification across approximately 300 ASX-listed companies and all major Australian sectors. However, it is concentrated in Australian shares only — adding VGS (international shares) significantly improves geographic diversification. VAS alone is not globally diversified.
Can you be over-diversified? Yes — owning too many funds with overlapping holdings (e.g., 5 different global share ETFs) adds complexity and potentially higher fees without meaningfully reducing risk. Two to four complementary ETFs — covering Australian shares, global shares, and bonds — provide sufficient diversification for most investors.
This article provides general financial information only. For advice tailored to your situation, speak with a licensed financial adviser through the ASIC financial advisers register or MoneySmart.