Three indices crossed the desk today. Only one of them can force a trade
Victoria Shinder3 min readThree constructed numbers arrived on this desk within two days of each other, and it is worth setting them beside one another, because they look like the same sort of thing and are not.
The first is the Export Similarity Index in the ECB's latest Economic Bulletin box, a measure going back to a 1979 paper, applied to Chinese and EU export baskets between 2019 and 2025. The second is NetDemand, invented in ECB Working Paper 3288, which counts whether press coverage attributes inflation to demand or to supply and sets the difference against inflation risk premia. The third is FTSE Russell's classification of Greece, moved from advanced emerging to developed on Monday, with STOXX doing the same on the same day.
All three are indices. All three compress something complicated into a number. And the third one belongs to a different species.
The difference is a contract
The similarity index tells you that German and Chinese export baskets overlap more than they did. Nobody has to do anything about that. A finance ministry can read it, argue with the sector classification, commission a rival measure, or ignore it. Its authority is entirely argumentative: it persuades or it does not.
NetDemand is a rung further out. It is a measure of a measure — a count of what newspapers said, used to stand in for a belief that was previously only inferable from the thing it was supposed to explain. That circularity is exactly the problem the paper is built to solve, and the solution's force is methodological. If the construction is wrong, the finding evaporates and nothing else happens.
FTSE's label does not work that way at all. It sits inside fund prospectuses and investment mandates as a term that has legal effect. When it changed on Monday, funds restricted to emerging markets had to sell 62 Greek stocks and funds mandated to developed Europe had to buy them, and the trading began before the effective date because everyone could read the calendar. No one was persuaded of anything. A word changed in a document and money moved.
Why the distinction is worth keeping
Because the second kind is quietly rarer than it looks, and the two get discussed in the same tone. Commentary treats a reclassification as a verdict on a country's progress — and Euronext Athens and the exchange's chief executive both described Monday that way, reasonably enough, in terms of reform and recognition. But the mechanism that actually moved shares on Monday was not recognition. It was the sentence in a prospectus that says which universe the fund invests in.
That has an uncomfortable implication running the other way. If a classification binds, then the methodology behind it is not merely an analytical choice; it is a rule with distributional consequences, set by a private firm, enforced through contracts nobody renegotiated. The ECB's similarity index can be wrong and the cost is a bad argument. A classification can be wrong and the cost is a forced trade at whatever price the forced trade clears.
None of which is an objection to any of the three. It is a note about how to read them. When a number arrives, the useful first question is not whether it is well constructed — that is the second question. The first is whether anyone is contractually obliged to act on it, because that determines whether you are looking at a description of the world or at a small piece of the machinery that runs it.