Risk management is arguably more important than stock selection. A great stock pick with poor position sizing can destroy a portfolio, while a mediocre pick with proper risk management will not. This guide covers institutional-grade risk management principles.
Position Sizing: The Kelly Criterion
Developed by J.L. Kelly Jr. in 1956, the Kelly Criterion calculates the optimal position size based on the relationship between risk and reward:
f* = (bp - q) / b
Where b = net profit per unit risked, p = probability of success, q = probability of failure.
Practical Application
- Full Kelly is too aggressive for real-world investing — portfolios become dangerously concentrated
- Fractional Kelly (half or third-Kelly) is the practical standard — it keeps portfolios on the safe side even when parameter estimates are wrong
- Adjusting for asset correlations is critical — correlated positions create unintended concentration risk
Position Sizing Rules of Thumb
| Portfolio Type | Position Size | Max Single Loss |
|---|---|---|
| Diversified | 2–5% per position | 1–2% of portfolio |
| Concentrated | 5–10% per position | 2–3% of portfolio |
| High-conviction | 10–15% per position | 3–5% of portfolio |
Diversification and Correlation
- Most diversification benefit is captured with 25–30 uncorrelated positions in equities
- The key is correlation — assets that move independently provide true diversification
- During crises, correlations spike (all risk assets sell off together), making alternative diversifiers valuable
- Factor diversification — combining value, momentum, and quality — provides a natural diversification layer since these factors have low inter-correlations
Understanding Drawdowns
| Event | Peak-to-Trough | Recovery Time |
|---|---|---|
| Great Depression (1929–32) | -86% | 25+ years |
| Dot-Com Bust (2000–02) | -57% | 13 years |
| Global Financial Crisis (2008–09) | -54% | ~4 years |
| COVID Crash (2020) | -34% | ~5 months |
Since 1928, the S&P 500 has experienced 15 bear markets (declines >20%). The critical math: a 50% loss requires a 100% gain to recover. This asymmetry makes drawdown prevention more valuable than return maximization.
Drawdown Management Strategies
- Pre-defined thresholds — Establish maximum acceptable portfolio drawdown before entering positions
- Systematic de-risking — Reduce equity allocation when drawdown exceeds a threshold
- Cash reserves — Maintain dry powder for deployment during severe drawdowns
- Rebalancing discipline — Systematically buy assets that have declined and sell winners
Portfolio Construction Principles
- Define target asset allocation based on risk tolerance, time horizon, and goals
- Evaluate portfolios by Sharpe ratio and max drawdown — not just raw returns
- Use factor diversification as a portfolio construction tool
- Consider drawdown tolerance: most investors overestimate their ability to hold through severe declines
Our stock rankings include stability scores (10% weighting) and timing signals to help identify lower-risk entry points. The backtest results show how the model's risk-adjusted returns compare to the S&P 500 across different market environments.