LOOK-AHEAD BIAS
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Using information in a backtest that would not have been available at the time decisions were made.
Summary
Look-ahead bias is a critical error in financial analysis and backtesting where researchers accidentally use future information that wasn't available at the time historical trading decisions were supposedly made. This creates unrealistically optimistic results because the analysis benefits from hindsight. It's like cheating on a test by looking at the answer key - the results look great but aren't achievable in real-world trading scenarios.
Usage Context
Understanding look-ahead bias is crucial when learning about backtesting methodologies, quantitative trading strategies, portfolio optimization, and financial research validity. It's particularly important when evaluating the credibility of trading systems and academic studies.
Common Confusions
- Thinking that using end-of-day data for intraday decisions is acceptable
- Believing that revised or restated financial data was available in its final form historically
- Assuming that corporate actions and stock splits can be applied retroactively without adjustment
- Using future volatility or correlation data to make past portfolio allocation decisions
