Diversification — Correlation and Concentration
Learning Objectives
After reading this chapter, you will be able to:
- Connect: A great portfolio is not the one that delivers the highest return, but the one that keeps the investor in the game for the long term
- Explain how diversification reduces risk
- Explain how unsystematic risk can be reduced
- Explain: 10–20 quality stocks are sufficient for most investors
Introduction
An old question in investing — "How many stocks should you hold?" Too few → risk rises. Too many → returns may fall. Understanding this balance is the art of diversification.
Core Concepts
Financial Terms
| Term | Meaning |
|---|---|
| Diversification | Spreading capital across assets, sectors, and companies |
| Systematic Risk | Market-wide risk (recession, war, interest rates, inflation) — cannot be eliminated |
| Unsystematic Risk | Company-specific risk — can be reduced through diversification |
| Correlation | How two investments move together |
| Concentration Risk | A large portion of the portfolio in a few holdings |
| Portfolio Variance | Measure of overall portfolio risk |
| Diworsification | Excessive diversification — hard to analyze, index-like returns |
Correlation Scale
| Correlation | Meaning |
|---|---|
| +1 | Move perfectly together |
| 0 | No relationship |
| -1 | Move in opposite directions |
Investment Decision
| Action | When |
|---|---|
| Diversify | Capital preservation matters, future uncertain, knowledge limited |
| Concentrate | Deep research, thorough business understanding, can bear risk |
"Diversification is protection against ignorance."
— Warren Buffett
Formula & Explanation
Portfolio Impact Example
Portfolio A: 100% in one stock — 50% fall = 50% portfolio loss
Portfolio B: 10 stocks × 10% each — one stock falls 50% = ~5% total impact
Law of Diminishing Returns
Beyond 30+ stocks, the marginal benefit of diversification often declines.
Visual Guide
Worked Example — Indian Market
Example 1 - Position Size
Cap single stock at 5-10% for most retail portfolios.
Example 2 - Rebalance
75/25 equity/debt after rally -> sell 15% equity mechanically.
Real World Example
Rohan invested all his savings in one company. An industry crisis hit, profits fell, and the stock dropped 70% — wealth was severely impacted.
Amit split investments across Banking, IT, FMCG, Pharma, and Infrastructure. The market fell, but the portfolio remained relatively stable.
Diversification exists not to maximize gains, but to avoid destruction.
Case Study
How Many Stocks Are Enough?
| Investment Style | Number of Stocks |
|---|---|
| Concentrated | 5–10 |
| Balanced | 10–20 |
| Highly Diversified | 20–30 |
Balanced Sector Allocation
| Sector | Allocation |
|---|---|
| Banking | 20% |
| IT | 20% |
| FMCG | 15% |
| Pharma | 10% |
| Manufacturing | 15% |
| Infrastructure | 10% |
| Cash | 10% |
Position Limit Framework
| Situation | Maximum Allocation |
|---|---|
| Single Stock | 5–10% |
| High Conviction | 10–15% |
| Single Sector | 20–25% |
CFA Exam Tip
A senior CFA analyst asks:
- Is any single stock overweight?
- Is sector exposure balanced?
- Is there hidden correlation?
- Are all companies affected by the same economic cycle?
- Are risks understood?
Low correlation between equity and gold can provide diversification. If the entire portfolio is in IT alone, an industry slowdown affects the whole portfolio.
Common Mistakes
- Excessive investment in one stock
- Entire portfolio in one sector
- Buying only popular stocks
- Not assessing risk
- Excessive diversification (diworsification)
Key Takeaways
Rule No. 1: Don't lose capital. Rule No. 2: Don't forget Rule No. 1.
A great portfolio is not the one that delivers the highest return, but the one that keeps the investor in the game for the long term.
- Diversification reduces risk.
- Unsystematic risk can be reduced.
- 10–20 quality stocks are sufficient for most investors.
- Excessive diversification can reduce returns.
- Both quality and balance are essential.
Practice Questions
Chapter: Diversification | Part 12 | Try before reading answers.
Q1 (Conceptual): Diversification — what is the core message of this chapter in one sentence?
Q2 (Calculate): Compute one Diversification metric for any NSE-listed company (latest FY).
Q3 (Application): How do Diversification and Systematic Risk interact in Diversification decisions?
Q4 (Red Flag): Red flag: Excessive investment in one stock — why avoid relying on Diversification alone?
Q5 (CFA Style): CFA-style trap when interpreting Diversification?
Q6 (Decision): Diversification looks strong but valuation stretched — invest, wait, or avoid?
Q7 (Lab): Complete one Diversification exercise in Part 12 Practice Lab.
Answer Key
Q1 (Conceptual)
A great portfolio is not the one that delivers the highest return, but the one that keeps the investor in the game for the long term.
Q2 (Calculate)
State formula, inputs (Rs. Cr or per share), result, and AR/Screener source.
Q3 (Application)
Both must align — strong Diversification with weak Systematic Risk (or vice versa) needs deeper AR review.
Q4 (Red Flag)
Excessive investment in one stock
Q5 (CFA Style)
A senior CFA analyst checks single-stock weight, sector balance, hidden correlation, economic-cycle overlap, and understood risks.
Q6 (Decision)
Usually wait for MOS unless quality exceptional. Also: Diversification reduces risk.
Q7 (Lab)
See Part 12 Practice Lab and verify with lab Answer Key.
Go deeper: Part 12 Practice Lab
FAQ {#faq}
Q: Diversification — what is the second check when evaluating this concept?
A: Entire portfolio in one sector — sector concentration defeats diversification even with many names.
Q: How do you connect theory with Indian market practice for Diversification?
A: Use Screener/Trendlyne plus annual reports — plot sector weights and pairwise correlations for your NSE holdings over 3 years; paper formulas alone are insufficient.
Q: diversification — why should you avoid this mistake?
A: Excessive investment in one stock leaves unsystematic risk undiversified — one corporate event can dominate portfolio returns.
Q: diversification — buying only popular stocks red flag — why avoid it?
A: Popular names often cluster in the same sectors and cycles, creating hidden concentration risk.
Q: How do I drill this chapter's concepts in the Practice Lab?
A: Open Part 12 Practice Lab → use the FAQ Drill row for diversification; verify answers in the Chapter FAQ Quick Index.
Practice Lab FAQ: Full part FAQ index — Part 12 Practice Lab
Related Topics
- Previous Chapter: 85-Asset Allocation Pro
- Next Chapter: 87-Position Sizing
- Part Overview: Part 12 Portfolio Risk
- Book Index: Full Table of Contents
Disclaimer: Educational content only. Not investment advice. Consult a qualified financial advisor before investing.