Backtesting
Lookahead bias
A research error where an analysis uses information that would not have been available at the simulated decision time.
- Timestamp alignment, revised data, and future labels are common sources.
Related: point-in-time data, data leakage, out-of-sample
Backtesting
Out-of-sample
Data reserved for evaluation after rules or parameters have been chosen on separate development data.
- Repeated tuning to the same evaluation set makes it part of the research process and weakens the evidence.
Related: walk-forward analysis, overfitting, validation
Backtesting
Transaction costs
The frictions that reduce implementable results, including fees, spreads, market impact, and other execution costs.
- Research that ignores realistic frictions can materially overstate performance.
Related: slippage, turnover, capacity
Educational boundary
This content is for educational and technical research purposes only. It is not financial advice, investment advice, trading advice, tax advice, or legal advice. Backtests and examples may contain errors or omissions. Past performance does not guarantee future results. Always test code in a safe environment before using it with real accounts or live trading systems.
InQuantWeTrust publishes educational content for quantitative research and analytical methods. It does not provide personalized advice, trade recommendations, managed services, or guaranteed outcomes.