The Two Lenses
A framework in quantitative trading where every metric is evaluated through both its theoretical statistical properties and its physical microstructure execution constraints.
Two questions have to be answered about any quantitative result before it means anything, and answering only one of them is the most common way research goes wrong.
The first lens is statistical. Is the effect distinguishable from noise, given everything that was tried in order to find it? That question cannot be answered without a trial count, which is why data snooping, the deflated Sharpe ratio and the kill ledger all belong to this lens. A result that survives it has earned exactly one claim: that it is probably not an artefact of searching.
The second lens is physical. Could the result have been obtained by an order actually sent to an actual venue? The constraints here are the ones a spreadsheet never enforces — the spread that had to be paid, the depth that existed at the price, the latency between decision and arrival, the requote or rejection that turns a fill into a non-fill, and the financing charged while the position was held. A result that survives this lens has earned a different claim: that it is executable.
The two failure modes are symmetric. A finding that passes only the statistical lens is a real pattern that costs more to harvest than it returns — the familiar short-horizon reversal that evaporates the moment execution cost is charged honestly. A finding that passes only the execution lens is cheap to trade and never had an edge to begin with; it will trade smoothly all the way down.
Neither lens outranks the other and neither substitutes for the other, which is also why the two must not be collapsed into a single headline number. A composite score hides which lens the result failed, and the two failures call for opposite responses: one is fixed by more evidence, the other by a cheaper way to trade — or by not trading it at all.