Liquidity filters, weighting rules, and index proxies in a same-category sleeve

A working set, not the sleeve

A same-category sleeve is a group of funds labeled as one market segment, such as small-cap blend, that can still differ in benchmark, weighting, size, and tradability. A mid-2016 same-sleeve review compared six small-cap blend ETFs. The small-cap blend sleeve contained more than 60 ETFs, so the six-name table was a reduced working set rather than the full category.

Those six funds recorded four distinct underlying benchmarks, so they were not interchangeable index proxies. An index proxy is a listed fund used as a stand-in for a stated benchmark; two proxies in the same sleeve may still track different indexes.

Assets under management across the six funds ranged from 57.9 billion dollars to 39.6 million dollars. Assets under management is used here as a viability and capacity check rather than a forecast of results. Five of the six funds were market-capitalization weighted. The sixth used equal weighting and rebalanced quarterly.

Apply the liquidity filter first

A liquidity filter is a pre-trade screen that drops vehicles whose volume, spread, or book depth would make the intended order costly or unexecutable. The working method treated high average daily volume as a liquidity filter because it was expected to coincide with narrower bid-ask spreads and faster execution.

The equal-weight fund showed a three-month average daily volume of 1,150 shares in the comparison table and was removed on liquidity grounds. A second fund was also removed after the liquidity filter because its three-month average daily volume was 16,566 shares, even though other tabulated fields were not outliers.

Equal weighting is a construction rule that assigns the same weight to each holding and typically resets those weights on a fixed calendar. In this working set that rule belonged to one fund, and that fund was dropped on volume, not because equal weighting and cap weighting are the same.

Differences that survived the screen

After weak-volume names were dropped, remaining candidates still differed in three-month average daily volume from 804,961 shares to 28.6 million shares. They still differed in expense ratio, fund size, holding count, and which index they proxied.

Implementation cost is the spread, impact, and related friction paid to enter or exit a position, distinct from a fund's stated expense ratio. Editorial reading: surviving the volume screen does not make a remaining fund the sleeve. Name the index proxy, keep the weighting rule visible, and treat fund size as a capacity check rather than a result.