Does a high Sharpe Ratio guarantee future profits?

No. A high Sharpe Ratio indicates efficient risk-adjusted returns in the past, but market conditions change. It does not predict future performance or eliminate the risk of loss.

What is a good Information Coefficient (IC) for a stock strategy?

In equity markets, an IC above 0.05 is often considered meaningful. Because stock prices are noisy, even small predictive correlations can be valuable if applied consistently across a large universe of stocks.

Why is Maximum Drawdown important if the strategy eventually recovers?

Maximum Drawdown matters because it tests investor psychology and capital preservation. Deep drawdowns may force investors to sell at a loss due to panic or margin calls, preventing them from benefiting from the eventual recovery.

Can backtesting predict exact future returns?

No. Backtesting simulates past performance to assess robustness and logic. It cannot predict future price movements, black swan events, or structural market changes.

What is Backtesting? Understanding IC, Sharpe Ratio & Max Drawdown

What is Backtesting? The Time Machine for Strategies

Backtesting is the process of testing a trading strategy against historical market data to evaluate how it would have performed in the past. Think of it as a flight simulator for pilots: before flying a real plane, pilots practice in a safe, virtual environment. Similarly, investors use backtesting to "practice" their strategies on years of past data without risking real capital.

The core assumption is that if a strategy worked consistently under various historical conditions (bull markets, crashes, sideways trends), it might be robust enough for future application. However, past performance does not guarantee future results. Backtesting helps identify flaws, such as excessive trading costs or vulnerability to specific market crashes, before live deployment.

The Information Coefficient (IC): Measuring Predictive Power

The Information Coefficient (IC) measures the correlation between your strategy's predicted returns and the actual realized returns. It answers the question: "How good is my model at forecasting?"

Range: IC ranges from -1 to +1.
Interpretation:

- An IC of +1 means perfect prediction. - An IC of 0 means no predictive power (random guess). - An IC of -1 means perfect inverse prediction.

Realistic Expectations: In quantitative finance, an IC of 0.05 to 0.10 is often considered significant. It’s like a coin toss that lands heads 55% of the time instead of 50%. Small edges, when compounded over many trades, can generate substantial results.

Sharpe Ratio: Balancing Return and Risk

The Sharpe Ratio is perhaps the most famous metric for risk-adjusted return. It tells you how much excess return you are receiving for the extra volatility you endure for holding a riskier asset.

Formula Concept: (Strategy Return - Risk-Free Rate) / Standard Deviation of Returns

Analogy: Imagine two drivers. Driver A goes 100 mph but swerves wildly. Driver B goes 90 mph but stays perfectly in the lane. Driver B has a better "Sharpe Ratio" because they deliver high speed with lower risk of crashing.
Benchmark:

- < 1: Suboptimal. - 1 - 2: Good. - > 2: Very good. - > 3: Excellent (but be wary of overfitting).

A high Sharpe Ratio indicates that the strategy’s returns are consistent relative to its volatility, rather than being driven by a few lucky, high-risk bets.

Maximum Drawdown (MDD): The Pain Threshold

Maximum Drawdown measures the largest peak-to-trough decline in the value of a portfolio. It represents the worst-case scenario loss an investor would have experienced during the backtest period.

Why it Matters: MDD tests your psychological endurance. If a strategy has a 50% MDD, you must be prepared to see half your portfolio value vanish before it recovers. Many investors abandon strategies during deep drawdowns, locking in losses.
Calculation: If your portfolio peaks at $10,000 and falls to $6,000 before recovering, the MDD is 40%.
Rule of Thumb: Lower MDD is generally preferred. A strategy with moderate returns but low MDD is often more sustainable than one with high returns but extreme volatility.

Avoiding Common Pitfalls: Overfitting and Look-Ahead Bias

When interpreting these metrics, beware of "overfitting." This occurs when a strategy is tweaked so specifically to past data that it fails in new market conditions. Always check if the strategy performs well in out-of-sample data (periods not used for optimization). Additionally, ensure your backtest does not suffer from "look-ahead bias," where the algorithm accidentally uses data that wasn't available at the time of the trade decision.

By understanding IC, Sharpe Ratio, and Maximum Drawdown, you gain a clearer picture of a strategy's true potential and risks, moving beyond simple profit charts to a deeper statistical evaluation.

本文為公開資料與方法論的科普整理，僅供學習參考，不構成任何投資建議。