Trading and Exchanges Chapter 23: Index Funds, ETFs, and Portfolio Trading

If you have money in a Vanguard or Fidelity index fund, or you buy SPY or VOO through your brokerage app, Chapter 23 is basically about you. Harris wrote this in 2003, but it reads like a prediction of what actually happened. Index investing went from a niche idea to the default way normal people invest. This chapter explains why.

What Are Price Indexes?

A price index is just an average of prices for a list of instruments. The Dow Jones Industrial Average is a price-weighted index of 30 stocks, where the highest-priced stock has the most influence. The S&P 500 is a value-weighted (capitalization-weighted) index, where the biggest companies by market cap matter most.

There are also equal-weighted indexes and geometrically weighted indexes, but most people never encounter those outside of academic research. The important thing is that most major indexes are value-weighted. When Apple or Microsoft goes up 1%, it moves the S&P 500 way more than when some small company does the same.

One detail people miss: the regular S&P 500 index does not account for dividends. There is a separate “total return” version that adds dividends back in. When you compare your portfolio performance against “the S&P 500,” you should technically be comparing against the total return version. Most people do not, which makes their returns look worse than they are.

How Index Funds Work

Running an index fund sounds boring, and it kind of is. For a value-weighted index like the S&P 500, the manager just buys a proportional slice of every stock in the index. If your fund is 0.01% of the total market cap of all S&P 500 companies, you buy 0.01% of every stock. Done. You only need to rebalance when the index committee adds or removes a stock.

For a price-weighted index like the Dow, you buy an equal number of shares of each component. Simple.

The catch is that index funds always slightly underperform their target index. Transaction costs from reinvesting dividends, handling investor deposits and redemptions, and rebalancing when the index changes all drag on returns. Management fees, even tiny ones, eat into performance too.

Harris mentions an interesting phenomenon around the annual Russell Index reconstitution. Every June, the Russell indexes reshuffle their components based on market cap. Index funds tracking Russell indexes all need to buy the additions and sell the deletions around the same time. From 1996 to 2001, the stocks being added outperformed the ones being removed by about 15% in June, then reversed by 5% in July. Basically, the predictable buying and selling pressure moves prices temporarily. If you know it is coming, you can front-run it. This same effect happens when S&P changes its components, which is why you sometimes see a stock jump just on the news of being added to the S&P 500.

The Zero-Sum Argument for Indexing

This is the mathematical heart of the chapter, and honestly one of the strongest arguments in the entire book.

Harris says: without transaction costs, the value-weighted average return of all portfolios must equal the market index return. This is not an opinion. It is accounting. All the shares have to be held by someone. If some people beat the index, others must trail it by exactly the same amount. It is a zero-sum game.

Now add transaction costs. Active managers trade a lot, sometimes turning over their entire portfolio more than once a year. They charge 1-3% in management fees. Passive index funds trade rarely and charge under 0.15%. After costs, the average active manager must underperform the index.

The data confirms it. In any given quarter, only about one-fourth of mutual funds beat the market. And the winners rotate. The fund that crushes it this year is not the same one that crushes it next year. As Harris puts it: luck matters more than skill for explaining short-term performance. The consistent losers, though, tend to stay losers. They lose because they trade too much.

Harris has a great line here. Active managers do not lose because they consistently buy instruments that fall and sell instruments that rise. They lose because they consistently buy and sell. The trading itself is the problem.

Why Index Markets Are So Liquid

Index products are cheaper to trade than individual stocks for three reasons. First, index dealers face almost no risk of trading with informed traders. Nobody has a real edge on where the entire market is going tomorrow. Second, everyone trades the same few index products, so there is tons of volume and tight spreads. Third, you only need to arrange one transaction instead of hundreds.

When traders do need to buy or sell all the stocks in an index at once, they use program trading. The NYSE and SEC define this as 15 or more coordinated transactions worth at least $1 million total. At the time Harris wrote, program trades were about 27% of NYSE volume.

ETFs and Other Index Products

Harris describes several ways to get index exposure. Open-end mutual funds are the simplest but you can only buy or sell at end-of-day prices. Exchange-traded funds (ETFs) trade all day like stocks and avoid the headaches of managing individual shareholder deposits and redemptions. Large institutional traders can create or redeem ETF units by depositing or withdrawing the actual underlying portfolio of stocks. This creation/redemption mechanism is what keeps ETF prices close to the actual value of the underlying stocks.

Index futures are popular with hedgers and speculators because they require small margins. The downside is you have to roll your position into new contracts when the old ones expire.

Package and Basket Trading

For institutional investors who need to trade entire portfolios at once, there is the basket trading market. You send a description of your portfolio to package dealers, and they quote you a firm price for the whole thing. Prices are usually expressed relative to end-of-day value, like “closing price minus 15 cents per share.”

Package dealers can offer better prices than you would get trading each stock individually because portfolio trades carry less information risk. If someone is selling a diversified basket, they are probably rebalancing or raising cash. They are probably not trading on inside information about 500 different companies at once.

Why This Matters Now

Harris was writing before most people had ever heard of an ETF. Now ETFs are arguably the most important financial product for regular investors. The logic he explains in this chapter is exactly why. Index investing is cheaper, simpler, and after costs beats most active managers most of the time. The zero-sum math has not changed.

If you are putting money into SPY or a target-date fund in your 401(k), you are doing exactly what this chapter suggests. You are accepting the market return, paying minimal fees, and letting the active traders fight over the scraps. It is not exciting. It is not glamorous. But the math is firmly on your side.

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Next: Chapter 24: Specialists