Correlation and Hidden Overlap
Diversification only works when holdings respond to different forces. Correlation is the measure of whether they actually do.
Why this matters for beginners
Many portfolios that look diversified are concentrated in one driver: one sector, one currency, one interest-rate assumption or one large customer.
Main explanation
Correlation describes how holdings move together. High correlation means diversification exists in name only.
Overlap hides inside funds. Several broad index funds often hold the same large companies, so combining them changes little.
Overlap also runs through shared drivers: suppliers to the same industry, companies dependent on the same customer, or businesses sensitive to the same interest rates.
A simple check is to write the main driver next to each holding. Repetition in that list is your real concentration.
Example using a real company
Three technology funds can each hold the same handful of large companies, so the combination is closer to one position than three.
- →Hidden overlap: two index funds sharing the same top ten holdings.
- →Shared driver: several holdings supplying the same single industry.
Common beginner mistakes
- ✕Treating multiple funds as automatic diversification.
- ✕Ignoring shared exposure to one customer or industry.
- ✕Assuming different tickers mean different risks.
Key terms
- Correlation
- The tendency of holdings to move together.
- Fund overlap
- The same companies held across several funds.
- Common driver
- A single factor affecting several holdings.
Key takeaways
- 01Diversification requires different drivers, not different names.
- 02Funds frequently overlap in their largest holdings.
- 03Listing each holding's main driver exposes concentration.
Check yourself
- 01Holding several funds can still leave you concentrated in the same companies.
- 02Different tickers guarantee different risk exposures.
- 03Writing down each holding's main driver reveals hidden concentration.
Try the concept on a real company
Check two funds or companies in the Analyzer and identify whether they depend on the same industry conditions.
Educational examples only. Not buy or sell recommendations.