Trading and Exchanges Chapter 10: How Informed Traders Move Markets (Part 1)
Chapter 10 is where Harris gets into one of the most important ideas in the entire book: how certain traders actually make prices accurate. Not because they want to help society. They just want to make money. The price accuracy is a side effect.
What Is an Informed Trader?
An informed trader is a speculator who figures out what something is really worth and then trades when the market price is wrong. They buy when things are cheap and sell when things are expensive. Simple concept. Very hard to execute.
Harris breaks them into four types: value traders, news traders, information-oriented technical traders, and arbitrageurs. We’ll get into each of those, but first let’s talk about what “really worth” actually means.
Fundamental Value vs Market Price
Every instrument has two prices. The market price is what you can buy or sell it for right now. The fundamental value is what the thing is truly worth if you account for all future cash flows, discounted properly, with all available information.
Nobody actually knows the fundamental value. If everyone had the same information and used the same models, they would agree. But that never happens. Traders disagree, and that disagreement is what creates the market.
The gap between market price and fundamental value is noise. Informed traders hunt for noise and try to profit from it.
Fun fact from the book: Fischer Black, the guy behind the Black-Scholes option pricing model, once said we should consider stock prices “informative” if they are between one-half and twice their fundamental value. One of the greatest financial minds ever basically said prices could be off by 100% and still be “close enough.”
How Informed Trading Makes Prices Better
Here is the mechanism. When informed traders buy undervalued assets, their buying pushes prices up toward fundamental value. When they sell overvalued assets, their selling pushes prices down. The net effect is prices that more accurately reflect reality.
Different informed traders usually have different estimates because they work with different data. When they trade with each other, their price impacts partially cancel. The resulting market price is a weighted average of their estimates. Harris calls the market a “statistical calculator” that aggregates information from many sources into a single price more accurate than any individual estimate.
And here is the natural selection part. Traders who estimate well get rich. Rich traders take bigger positions. Bigger positions move prices more. So over time, the market gives the most weight to its best estimators. Bad estimators lose money and leave. The market literally evolves toward better price accuracy.
The Paradox Nobody Talks About
Informed traders make prices accurate, but they do not trade for that purpose. They trade to make money. The price impact of their trading is actually a cost to them. They want prices to be wrong when they enter, and correct only after they are done.
So they need two things: liquid markets (so trades do not move prices too much) and prices that differ from fundamental values (so there is profit to capture). Too efficient? Nothing to trade on. Too illiquid? Trading costs eat the profits.
The Four Types of Informed Traders
Value traders are the deep analysts. They estimate the entire fundamental value using all available data: sales, costs, interest rates, management quality, competition, growth options. They hire teams of analysts, economists, statisticians. Their organizations are pyramid-shaped with many layers of review to prevent bias. Slow but disciplined. One failure mode: if the auto analyst uses a 10% discount rate while the airline analyst uses 5%, the firm will systematically undervalue cars relative to planes. Consistency matters.
News traders are the fast ones. They assume the current price is roughly correct and estimate how new information changes that value. Speed is everything because once information is “in the price,” it is stale and useless. They use flat organizations with few management layers so decisions happen fast. Great example from the book: when Pfizer got FDA approval for Viagra in 1998, the stock went from 95 to 113 in a month. First traders to understand what that approval meant made money. Everyone late missed the move.
Pseudo-informed traders are the trap Harris warns about. They think they are trading on information, but it is already in the price. They buy after good news pushed prices up. They sell after bad news pushed prices down. They feed profits to the actually informed. The most common mistake in trading is trading on stale information.
Information-oriented technical traders look for predictable price patterns from systematic mistakes by other traders. If news traders consistently overreact to earnings announcements, a technical trader can sell into that overreaction and profit when prices correct. But this is hard because once traders notice their mistakes, they fix them. Strategies that worked in the past stop working as markets mature. Harris also points out a biological reason we are bad at this: humans are wired to see patterns everywhere, even when none exist. Our ancestors who saw a tiger that was not there survived. Those who missed a real tiger did not. We inherited the pattern-seeing brain, which is terrible for chart reading.
The Takeaway So Far
Markets get their prices right not because of some magical invisible hand, but because smart traders constantly hunt for mispricings and profit from correcting them. The whole system runs on self-interest. But if you think you are informed, you better actually be. On the other side of your trade, there is probably someone with more data, better models, and a faster connection.
Part 2 will cover arbitrageurs and the famous efficient markets paradox.
Previous: Chapter 9: Good Markets
Next: Chapter 10: Informed Traders and Market Efficiency (Part 2)