When you buy an index, you're not buying diversification — you're increasingly buying concentration into one trade (AI/semiconductor).
| Index | Const | Eff-N | Top-10 | AI-core | Top-10% | Largest |
|---|---|---|---|---|---|---|
| KOSPI (Korea) | 830 | 6.9 | 64.9% | 53.0% | 90.9% | Samsung Electronics 29.2% |
| DJIA (US, price-wtd) | 30 | 20 | 55.4% | 15.9% | n/a | Goldman Sachs 11.7% |
| Nifty 50 (India) | 50 | 24 | 52.9% | 0% | 36.8% | HDFC 10.6% |
| NASDAQ-100 | 103 | 33 | 46.1% | 53.9% | 46.1% | Apple 8.2% |
| EURO STOXX 50 | 55 | 33 | 41.1% | 14.0% | 28.7% | ASML 8.7% |
| S&P 500 | 505 | 48 | 37.2% | 35.7% | 62.5% | Apple 7.7% |
| MSCI EM | 1,190 | 32 | 35.5% | 31.9% | 65.2% | TSMC 14.9% |
| MSCI World | 1,273 | 94 | 26.1% | 26.7% | 59.7% | Apple 5.5% |
| TOPIX (Japan) | 1,638 | 107 | 23.2% | 8.0% | 79.2% | MUFG 3.6% |
concentration measures, computed by us from each index's own full constituent file (July basis) Eff-N = how many equal-weight stocks the index really behaves like. AI-core = share of the whole index in the AI complex — chips + hyperscalers, now tracked as a live series per index.
The reading — and its limits
Three exceptions prove the point — Japan (TOPIX) is genuinely diversified (behaves like 107 stocks, AI-core just 8.0%); India (Nifty) is concentrated but in the old economy (AI-core 0% — its "tech" is IT services, the AI-disrupted category, not AI hardware); and the Dow (DJIA) sits near the top by top-10 (55.4%, second only to Korea) but this is a price-weighting artefact — its weights track nominal share price, not company size, so two high-priced blue-chips (Goldman, Caterpillar) dominate and the AI names (Nvidia, Microsoft) are muted. The Dow's low AI-core (15.9%) does NOT mean it escapes the AI trade — it holds the same names, down-weighted by share-price accident. Everywhere else, buying the index increasingly means buying the same handful of AI names. (July: the AI-hardware pullback trimmed AI-core in six of nine indices and lifted Apple back above Nvidia as the largest single holding in the S&P, NASDAQ and MSCI World — the concentration stands, but the trade breathes.)
Method Effective-N and concentration measures computed by us from each index's own full constituent file (index-owner or full issuer-holdings files). AI-core on a named-basket definition (semiconductors + hyperscalers) that crosses GICS sectors.
Computed 1 August 2026