Immutable. This exact content is served forever at /api/v1/blob/f1338cf5c93a1252.
--- name: backtest-look-ahead-in-universe-selection description: Use when auditing strategy universe selection logic to detect and prevent lookahead bias (e.g. selecting top 50 S&P 500 stocks by today's market cap retroactively for 2015 backtests). domain: algorithmic-trading subdomain: backtesting-methodology tags: - backtesting-methodology - universe-selection - lookahead-bias - point-in-time - survivorship-bias brokers_frameworks: - Universe Lookahead Auditor - Python version: '1.0' author: algo-trading-skills-contributors license: Apache-2.0 --- ## When to Use Invoke this skill when building or validating strategy universe selection rules. Selecting assets for a historical backtest using present-day attributes (e.g., "top 50 stocks by market cap today" or "current S&P 500 constituents" applied to 2015) introduces severe lookahead and survivorship bias. This skill audits universe membership point-in-time timestamps to guarantee zero future data leakage. ## Prerequisites - Point-in-time historical universe constituent records with publication dates. - Universe selection filter logic. ## Workflow 1. **Extract Constituent Timestamps**: Record the exact timestamp when symbol membership became known. 2. **Audit Filter Execution**: Assert that selection criteria (market cap, volume) use data strictly preceding backtest date $T$. 3. **Flag Lookahead Violations**: Alert if any constituent added to historical universe relied on post-date data. > Full procedure: see `references/workflows.md`. > Standards reference: see `references/standards.md`. > Printable pre-flight checklist: see `assets/checklist.md`. ## Common Pitfalls - **Retroactive Index Composition**: Using 2024 S&P 500 constituents for a 2015 backtest, excluding companies that went bankrupt. - **Using Un-adjusted Historical Caps**: Ranking universe by unadjusted market caps without point-in-time share counts. ## Verification - Submit universe selection with future-dated market caps, verify audit violation flag. - Run `python scripts/test_universe_lookahead_auditor.py` and confirm 100% pass rate. ## Related Skills - `backtest-database-schema-for-point-in-time-queries` - `backtest-survivorship-bias-auditing` ---