Published 2026-10-14
Universe
The universe is the set of instruments a strategy is allowed to trade. It decides the answer before the strategy even runs — and it is where survivorship bias most often hides.
On this page
What it is
The universe is the set of instruments a strategy is allowed to trade.
A rule that “buys the top 10 stocks” is meaningless until you say: the top 10 of what.
Why it decides the answer
The universe is not a neutral filter. It quietly encodes a view:
| If the universe is | Then |
|---|---|
| Today’s index members | Failed and delisted names are already gone |
| Names that still exist | Survivorship bias |
| Filtered by today’s liquidity | You are trading names that only qualified later |
Choosing the universe is part of the strategy, not preparation for it.
How to check
Ask how the universe was built, and at what point in time. A universe assembled from what exists today has used the future to decide what to test.
See point-in-time data for the fix.