FactorSage

Backtesting · Lesson 3.4

Point-in-time universes

A point-in-time universe is the list of stocks that were actually members of an index on a given historical date — not today's membership applied retroactively.

Why this matters

If a strategy can buy stocks that were not in the index on the test date, the backtest is using information that a real investor could not have used. That inflates results and hides survivorship bias.

FactorSage and S&P 500 history

FactorSage maintains S&P 500 membership across the last 30 years and uses that history when you backtest against the S&P 500 universe. Stocks are only eligible on dates when they were genuine constituents.

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