Market Participants in Equity Trading

For a market maker, the useful way to classify participants is not by what they are called but by how likely they are to know something you do not. That determines whether their flow is profitable to trade against.

Retail investors

Individuals trading their own accounts, in small size. Collectively large, individually not.

Retail flow is generally uninformed in the trading sense: it is driven by savings, sentiment or convenience rather than superior short-term information. That makes it the most attractive flow to take the other side of, which is why wholesalers pay brokers for it. Payment for order flow is controversial, and the economics behind it are straightforward: this flow rarely knows anything, so trading against it is profitable.

Institutional investors

Pension funds, mutual funds, insurers and asset managers, moving large size.

Their information content varies enormously. An index fund rebalancing is completely uninformed, trading for mechanical reasons on a published schedule. An active manager acting on fundamental research may be genuinely informed, though usually over horizons far longer than a market maker cares about.

What always matters about institutional flow is size. A large order moves the market, so it gets worked over time, and recognising a worked order is valuable because it tells you more of the same is coming.

Hedge funds

The most likely to be informed, and the flow to be most careful about. Some are explicitly trading on short-horizon signals, which is precisely the horizon that hurts a market maker.

Market makers

Firms quoting both sides continuously, including your competitors. They provide the liquidity everyone else consumes, and they are covered throughout the markets course.

Brokers

Intermediaries routing orders. They do not usually take positions; they connect clients to venues, and increasingly they run the algorithms that decide how a large order is executed. Their obligation is best execution for the client.

Why the venue tells you something

Because different participants trade in different places, the venue itself carries information about who you are likely to be facing.

Retail flow concentrates with wholesalers and certain venues. Institutional flow gravitates to dark pools and block venues to hide size. Fast participants concentrate where latency infrastructure is available.

This is why the same instrument can support different spreads on different venues, and why "quote where the flow is uninformed" is a real strategy rather than a slogan.