[pierrealexandre]

Are you aware of the distionction between market orders and limit orders?

HFTs by themselves can provide liquidity (like any other investor), namely by entering a limit order in the order book. They can also by themselves narrow the bid-ask spread, namely by entering a limit order at a price more competitive than the current first limit.

Of course, someone else has to send a market order to the exchange for a trade to execute.

[pdonis]

> Are you aware of the distinction between market orders and limit orders?

Yes.

> HFTs by themselves can provide liquidity (like any other investor)

Exactly: like any other investor. Meaning, the "high frequency" part of HFT is not what provides the liquidity. (I admit that I should have made that clearer in my previous post.)

Suppose an HFT enters a limit order that is more competitive than the current limit. Either some other investor would have been willing to trade at the same price (as the HFT's limit order), or not. If not, then it doesn't matter how fast the HFT places the limit order; it's going to increase liquidity in any case. So the "high frequency" part is not necessary; the key is that the HFT is an investor willing to trade at a certain price.

But if some other investor would have been willing to trade at the same price, then the only difference the HFT makes is speed: the liquidity gets added sooner than it otherwise would have. So the "high frequency" part doesn't change anything except who the profits from the trade go to.

[tptacek]

The "high frequency" in HFT compared to human traders is a little like the "high fructose" in HFCS compared to table sugar. To wit: "high frequency" changes the relationship of HFT to other sell-side traders; it's what allows HFT shops to potentially outcompete human market-makers.

However, it's the category of sell-side traders in general that matters for liquidity.

You're using imprecise language here (for instance, referring to market makers as "investors"), but the clear implication is that you believe that normal, "buy-side" investors provide adequate liquidity. But they don't, and we know that, because the more competitive the sell-side gets, the lower spreads get.

[pdonis]

> you believe that normal, "buy-side" investors provide adequate liquidity

Well, of course that depends on how you define "adequate". What is all this incessant trading of stocks for? What value does it provide? For example, if I'm an investor (a "real" one, not a market maker, to use less imprecise language) with a long time horizon, something like 30 years, because I'm saving for retirement, how does HFT make me better off?

[tptacek]

One obvious benefit of "incessant trading of stocks" is that buy-and-hold investors can move in and out of a position for much less than they could in the 80s. The "incessant trading" reduces costs, which can be very important even to value investors when there is some extrinsic prompt to trading.

[pdonis]

> buy-and-hold investors can move in and out of a position for much less than they could in the 80s

In other words, brokerage fees, or the equivalent, should be lower, so the overhead to execute a trade is lower. That has some value, yes, but not a lot, because a buy-and-hold investor, of course, doesn't execute many trades, so the overhead cost of executing trades is already pretty small for him.

Also, most "buy-and-hold" investors hold mutual funds, not stocks, which changes things. See below.

> costs...can be very important even to value investors when there is some extrinsic prompt to trading

Yes, but as I just noted, most "buy-and-hold" investors are holding mutual funds, not stocks, so they aren't paying the direct costs of stock trading anyway. When I want to rebalance my 401k, I don't trade stocks, I trade mutual fund shares, and they're all shares of different funds offered by Fidelity or Vanguard or whoever my 401k provider is. (And with most 401k's, certainly with the ones I have, as long as you don't rebalance too often there is no fee for rebalancing.)

So decreasing the overhead cost of trading will only appear to me, if at all, as a decrease in mutual fund fees; but with most 401k's the individual doesn't see those anyway, because they're provided through employers. I don't know how much the fee question affects the negotiations between employers and mutual fund providers for setting up 401k's, but in any case that's at least two layers of indirection between me as a retirement investor and the overhead cost of executing individual stock trades.

So I can see some small benefit, yes, but is it enough to offset the high social cost of having so many smart people doing HFT instead of something more productive?

[tptacek]

NO. Not "brokerage fees".

Whatever you pay to your brokerage, you pay on top of the spread. The spread is what you pay to place a market order.

In exchange for the privilege of buying right now, you pay the best offer price. In exchange for the privilege of selling right now, you pay the best bid price.

It's a commission you pay per share; the more shares you try to move, the more you pay whoever's providing you the liquidity.

[gd1]

The speed for a market maker (largely passive and posting limit orders) isn't about how fast you can place a limit order, it is about how fast you can cancel it. It is a defensive mechanism against predators who are even quicker (arbitrageurs, aggressive HFTs).

Imagine that there is a "true price" of some security at price x, and your bid and your offer are positioned around that true price at x - d (your bid) and x + d (your offer). So your spread is 2d. Then some external (public) event happens, which moves the true price by an amount greater than d. Let's say it is a big event, and the true price falls by 4d. Now there is a race. If you don't manage to cancel your bid in time, a predator will 'pick you off', take out your bid, and they'll sell to you at (x - d) when the true price is now (x - 4d). The predator has made an immediate (paper) profit of 3d, and you've made a loss of the same amount. If you're fast enough, you can successfully cancel your bid and repost it further down the book at x - 5d.

Now, as a market maker, a liquidity provider, you could increase your safety margin by quoting a wider spread, setting your bid and offer at +- 2d instead of +- 1d. Now it takes a larger move before you're in danger of being "picked off", but you'll also attract less customers and make less profits. Speed (latency) is directly correlated to how tight a spread a market maker can quote.

[pdonis]

What benefit do tighter spreads and faster response times provide to ordinary investors, like me with my retirement fund? I understand how they benefit the market makers; you've explained that. But all that really determines is who takes losses when an exogenous event that affects the underlying fundamentals of a stock gets reflected in its price. That's a zero-sum exchange: the market maker's loss is the predator's gain. How does all this create value on net?

[gd1]

So you've accepted that greater speeds allow market makers to quote tighter, so the answer is pretty simple. The tighter a market maker is quoting the less money he is making per transaction (smaller spread), so less money is leaving the system and going to middlemen. The speed allows them to undercut other market-makers and steal their 'flow' (customers) while still being able to avoid predators, and so they offer the service cheaper. The service being the provision of liquidity to bridge time gaps in a continuous time market.

If you assume that the number of 'real' trader (not middlemen) who want to buy or sell is constant (not necessarily true, but assume it for a moment), then it stands to reason that the tighter the spread, the less the market makers are profiting. At a small enough spread, they make no profit, since the profit from the flow on both sides is cancelled out by the losses from adverse selection (trading when they couldn't cancel in time - being victim to a predator). But if they can increase their speed, and minimize their adverse selection losses, then they can quote tighter and still make a profit. And do it with machines, and cut overheads of hiring humans, and you can quote even tighter since you need less trading profit to make a net profit. So this is the value generated, automation + speed = the smallest amount of frictional costs being extracted from the market.

[pdonis]

> automation + speed = the smallest amount of frictional costs being extracted from the market.

Ok, this makes sense. But it still leaves the question, how much are the frictional costs decreased by HFT, and is that benefit enough to offset the social costs?

[pas]

> social costs?

Such as? All I heard was smart boys and girls go and do a quantitative finance degree instead of Solve The World's Problems degree.

And that's bullshit. The social cost of _not_ providing other, better alternatives to our youth (downsizing NASA, underfunding research and scientific endeavors), lack of patent reform, lack of bandwidth and unified cross-country 3G/4G has much worse costs.

[kasey_junk]

If you need to buy/sell right now, having tighter spreads means that the price is cheaper for you. Your retirement fund, they need to buy/sell right now all the time, to re-balance their portfolio, whether for risk or for benchmark tracking, cash allocations, etc.

[pdonis]

See my response to tptacek upthread.

[kasey_junk]

Saw your response and I'd offer the following: A) the advantages that automation bring to the markets impact every single trade there is. Even if we take a very tiny sample of people who need to rebalance their EFTs today. Each day it is a tremendous savings. B) HFT is a tiny part of the finance industry, yet it has had a huge impact on the cost of trading, to the end result of trading being phenomenally cheaper than it has ever been.

Is that enough of an advantage to outweigh the cost of the small number of intelligent people in HFT? I don't know, but it certainly seems easier to justify than the phenomenal amount of capital spent on internet ads. I'm a bit of a free market capitalist, so my biased response is how else should we allocate people's output?

[rsync]

There is a (false) assumption among laypeople that limit orders "no longer work".

This (false) assumption is propagated regularly by articles and books wherein the same pattern repeats itself:

1. limit orders are defined

2. "... but on that morning Joe Trader was shocked to see that his limit orders weren't working!!"

3. description of Joe Trader NOT using limit orders ... or using them and canceling them and chasing prices ... or whatever.

I've seen this pattern in a lot of media since the Lewis book. In reality, limit orders haven't changed and you can set a limit and go to sleep / go on vacation, just like you always could.