An index provider's classification decision can move more money into a country than a year of economic news. The mechanism is mechanical rather than analytical.
Passive funds must hold what the index holds
A fund promising to track an index has no discretion over composition. When a constituent is added, the fund must buy it to keep tracking error low.
The amount involved is proportional to the total assets tracking that index. For the most widely followed benchmarks, this is a very large pool of committed capital.
The buying is not a judgement about value. It happens whether the addition looks expensive or cheap, which is why inclusion events distort prices around the effective date.
How a market qualifies for inclusion
Providers assess market size, liquidity and the practical experience of foreign investors operating there. The last category covers account opening, settlement, custody and the ability to repatriate proceeds.
Reclassification from one tier to another typically follows a consultation with the institutions that use the index. The process runs over years rather than months.
Countries often make specific regulatory changes to satisfy these criteria. The prospect of index-driven inflows is a real influence on capital market policy.
Why the flow arrives before the effective date
Active managers and market makers anticipate the passive buying and position ahead of it. Much of the price move therefore occurs between announcement and implementation.
Index funds themselves usually trade at or near the close on the effective date, aiming to match the index price rather than the best price. The two objectives are different.
Providers have responded by phasing large inclusions over several stages. Spreading the change across review dates reduces the concentration of orders at any single close.
What accessibility rules require of a country
Foreign ownership limits, restrictions on currency conversion and pre-funding requirements all reduce a market's assessed accessibility. Each raises the cost of tracking the index accurately.
Providers weight constituents by the shares actually available to foreign buyers rather than total shares outstanding. State holdings and strategic stakes are excluded from that calculation.
A country can therefore be economically large and index-small at the same time. The measure describes investability rather than the size of the underlying economy.
Why the effect fades
Once the flow is complete, the ongoing demand is limited to new money entering those funds. The one-off repricing is not repeated.
Part of the initial move typically unwinds over the following months as the anticipatory positions are sold back. The lasting change is in liquidity and analyst coverage rather than in valuation.
Exclusion works the same way in reverse and can be more disruptive. Forced selling into a market that has already been downgraded finds few willing buyers.