Investing & Portfolio
Investment Philosophies
Damodaran takes seven investment philosophies, from charting to indexing, and runs each one against the academic evidence rather than the sales pitch. He will not sell you a system: his recurring finding is that paper portfolios beat the market while the real funds running those same strategies do not.
The one idea
An investment philosophy is not a strategy. It is a belief about how other investors make mistakes. Damodaran's argument is that every approach that has ever beaten the market did it by harvesting one specific human error: crowds pile in and push prices too far (so you go contrarian), or crowds are slow to absorb news (so you ride momentum), or crowds ignore companies nobody writes about (so you go where the analysts are not). Name the error first. The strategy is just the tactic you use to collect on it.
That distinction is not academic housekeeping, it tells you when to quit. If you buy low price-to-book stocks because a study said they returned more, you have no idea what to do when they stop returning more. If you buy them because you believe investors chronically overpay for growth and underpay for assets already in the ground, you can watch whether that belief is still true and act on the answer. Damodaran's second reason is blunter. Investors with no core belief drift from strategy to strategy chasing whatever worked last year, and they pay for the drift in commissions, spreads and taxes.
The third piece is that there is no best philosophy, only a best fit. Buying beaten-down losers needs five years of patience and the stomach to read nothing good about anything you own. Activist value investing needs enough capital that management has to take your call, plus the willingness to fight in public. Venture investing needs you to accept that most of your bets die and a handful carry the whole fund. If your temperament, your account size, your time horizon or your tax situation does not match the philosophy, you will abandon it at the worst possible moment, which is the one reliable way to lose money.
What it actually teaches
Damodaran gives an explicit sequence for arriving at a philosophy, and the fourteen chapters are built to walk you through it in order.
BUILD THE TOOLKIT FIRST
Three skills before anything else: measure risk, value an asset, and price the cost of trading. He insists you do not need to be a mathematician, but the third skill is the one most readers skip and it is the one that kills strategies. His illustration: a paper portfolio of small US stocks (CRSP Small Stocks) and a real fund passively holding the same names (the DFA Small Stock Fund) drifted apart by roughly 2% a year from 1982 to 1991, purely from trading and execution costs. Every strategy later in the book has its own version of that gap.
NAME THE MISTAKE YOU ARE BETTING ON
Pick one of four views of markets. Markets overreact, so you go contrarian (buy losers, buy low multiples, fade the crowd indicators). Markets learn slowly, so you go momentum (relative strength, trend lines, buying after positive earnings surprises). Markets make both errors at different times, so you go opportunistic (arbitrage, pattern trading). Or market errors are random and unfindable, in which case you index. He is firm that you cannot mix strategies from contradictory views over the same holding period: buying on relative strength and buying stocks right after terrible earnings news are bets against each other.
TEST IT LIKE SOMEONE TRYING TO KILL IT
Six cardinal sins: leaning on anecdotes, testing a rule on the same data you extracted it from, biased samples, no control for how the market did, no control for risk, and reading correlation as cause. Four lesser sins: data mining, survivorship bias, ignoring transaction costs, ignoring execution. His number for survivorship comes from Carhart: about 3.6% of US equity funds died every year from 1962 to 1995, and roughly 80% of the ones that died had already lagged for five years. Leave them out and you overstate fund returns by 0.17% at a one-year horizon and by more than 1% at twenty years.
READ THE SCOREBOARD BEFORE YOU PICK
The evidence chapters exist to be graded, not admired. Low price-to-book and low PE deciles did beat high ones in the US across 1927 to 2001 and in France, Germany, Japan and the UK, but the margins are modest (the 1981 to 1992 international study added 1.06% a year in the US and 1.88% globally for low price-to-book) and they depend on your risk model being right. High PE growth screens lost to value screens on both equal-weighted and value-weighted bases from 1952 to 2001. Market timing needs you to be right somewhere between two-thirds and seven times in ten just to break even after costs. Active funds lost to their index in every style box.
MATCH IT TO YOURSELF
Patience, appetite for risk, whether you can stand being alone in a position, screen time available, age, job security, account size, cash needs and tax bracket. The hardest number in this section: small caps beat large caps only about half the time at holding periods up to five years, no better than a coin flip, and win decisively only beyond five years. Table 14.1 sorts every strategy in the book by time horizon and market belief, and prints in italics the ones that are simply not available to a small investor: activist value investing, venture and private equity, and pure arbitrage.
SET THE HOLDING PERIOD AND GUARD IT
The holding period is part of the strategy, not a preference you get to change later. Price momentum runs roughly six to eight months. Reversals take three to five years. In Jegadeesh and Titman's data the winner portfolio actually beat the loser portfolio for the first twelve months, losers needed 28 months to pull ahead in the 1941 to 1964 period, and never pulled ahead inside 36 months in the 1965 to 1989 period. Second rule here: one screen may work, three usually work worse, because screens undercut each other and wreck your diversification (a low PE screen hands you a portfolio of banks and utilities).
REVISIT WITHOUT CHASING
Stay consistent with the philosophy, but abandon it when the evidence turns against it, not when the last quarter turns against it. He notes the specific way screens die: publicity. Once a screen's success is written up and a crowd starts running it, they build the same portfolios and compete away the very excess return that attracted them. So a screen that works needs re-testing at intervals, and a screen everyone knows about is already suspect.
What it looks like Monday morning
You write down, in one sentence, which mistake other investors are making that your portfolio is set up to collect on. If you cannot write that sentence, Damodaran's position is that you do not have a strategy, you have a habit. Then check that your holding period matches it. If you own low price-to-book stocks and you get restless after six months, the evidence in this book says you will never see the return you bought them for, because the entire measured premium shows up over five years and longer.
The second job is faster. Pull up every fund you own and check the four things the book says predict underperformance: an upfront load, a high turnover ratio, a large cash position, and a stated style the fund does not actually hold. The average US equity fund charged about 1.78% a year in 2001, which is the hurdle it had to clear before you saw a dollar. Then look at the after-tax return rather than the headline number. Across 1997 to 2001 the after-tax return on the large active funds ran roughly 40% below their pre-tax return, while the gap at index funds was small.
| Measure | Excellent companies | Unexcellent companies |
|---|---|---|
| Growth in assets | 10.74% | 4.77% |
| Growth in equity | 9.37% | 3.91% |
| Return on capital | 10.65% | 1.68% |
| Return on equity | 12.92% | -15.96% |
| Net margin | 6.40% | 1.35% |
| $100 invested Jan 1981, value by 1986 | $182 | $298 |
Damodaran flags that this study did not adjust for risk, so read the gap as evidence that quality is often already in the price, not as a settled result.
there is potential for success with almost every investment philosophy (yes, even charting) but the prerequisites for success can varyDamodaran, Investment Philosophies
Where it fails
- The evidence stops in mid-2002 and the central finding reversed after that. The book's spine is that value screens beat growth screens over long periods, shown in decile returns running 1952 to 2001. From roughly 2007 through 2020 in US markets, high PE growth beat low PE value for well over a decade, one of the longest and deepest reversals on record. Every return figure quoted here (the price-to-book deciles, the PE deciles, the PEG results, the small cap premium) is a series that ends in 2001. Damodaran rewrote large parts of this material for the 2012 second edition. If a number from this page is load-bearing for you, it comes from the first edition.
- Roughly half the philosophies he covers are ones he tells you that you cannot use. Table 14.1 prints in italics the strategies not feasible for small investors, and the list is long: activist value investing, activist growth investing (venture capital and private equity), and pure arbitrage. He is explicit that pure arbitrage in futures and options is available only to institutions with near-zero transaction costs and the ability to borrow at close to the riskless rate, and that the average gross profit on an S&P 500 index arbitrage trade was 0.30%. He is honest about all of this, but the title does not warn you that several chapters are spectator sport.
- There is no method here, by design, and the book's own evidence shows why. Chapter 8 lists Ben Graham's ten screens in full, then immediately reports that James Rea built the Rea-Graham fund on them in the 1970s and it floundered through the 1980s and early 1990s, finishing in the bottom quartile for performance. That is the book in miniature. It hands you the scoreboard, tells you the paper portfolios worked, tells you the real funds running them did not, and leaves the reconciliation to you. Readers who want a rule set will finish the book with a reading list instead.
- The first 130 pages are a corporate finance textbook bolted to the front. Chapters 2 through 5 cover risk models (CAPM and APT), financial statement analysis, discounted cash flow valuation, and trading costs and taxes, before you reach a single investment philosophy. If you already know that material it is dead weight. If you do not, you will stall in it and never reach chapters 7 through 13, which is where the book actually earns its place. The graded verdicts start at chapter 7, and a reader short on time should start there and come back.
- His exemplars are survivors, which is a sin he names in his own methodology chapter. Chapter 6 lists survivorship bias as one of the errors that corrupts strategy testing, and he applies the correction rigorously to fund data (Carhart) and to venture capital, where he points out that in 1999 the weighted-average private equity IRR was 119% while the median was 2.9%. Then the philosophy chapters are anchored on Buffett, Peter Lynch and Michael Price. He does give three good reasons Buffett's record cannot be replicated (the market changed, the later Buffett is an activist needing scale and credibility, and Berkshire's shareholders let him be patient), but there is no counterpart profile of anyone who ran the same playbook and failed.
- It never crosses from 'this has positive expected excess return' to 'this is how much I put in.' Position sizing, risk of ruin and drawdown tolerance are absent. The closest the book gets is repeated instructions to diversify and one observation that a screened portfolio can end up concentrated in a single sector. For a book whose whole point is matching a strategy to your own capital and cash needs, the gap between an academic excess return and an actual allocation is left entirely to the reader. Anyone building a rules-based system will need a second book for the risk management layer.
Who it is for
Buy it if
You already run a strategy and you want to know whether the evidence actually supports it. You are the reader who wants the referee's report rather than the coach's pep talk, and you can sit with a conclusion like 'this works, but only past five years, only if your costs are near zero, and only if you can name the human error it feeds on.' Portfolio managers, serious self-directed investors, and anyone constructing a rules-based system will get more out of this than out of ten trading books.
Skip it if
You want something you can trade on Monday. Damodaran endorses no screen, no entry rule and no exit rule without three conditions attached, and he marks several of the philosophies he covers as unavailable to small accounts. If you lose patience with decile return charts running back to 1927, or you came looking for war stories about great trades, you will not get past chapter 5.
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Reviewed here is the 2003 first edition. The link goes to the second edition (2012), which re-ran the return data. Every decile figure quoted above has a 2001 cutoff and differs in the edition you will receive.
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