Factor investing.

In plain English

Factor investing selects securities by characteristics such as a low price relative to book value, small company size, recent momentum, low volatility, or high profitability, rather than by company-by-company judgment. The approach grew out of academic work showing that a market-exposure model alone left a lot of return variation unexplained, and that certain traits explained more of it. Funds built this way are sometimes marketed as smart beta, sitting between index tracking and traditional active management in cost and in how far they stray from the market. Factors go through long stretches of underperformance, sometimes a decade or more, which is the practical difficulty. Whether a documented factor reflects extra risk being compensated, a behavioral pattern, or a result that only appeared because researchers tested many combinations is still argued.

01Why it matters

A factor fund can trail the plain market for many years while the research behind it stays intact, so the holding period required is longer than most people expect when they buy it.

02The math, step by step

A value factor fund and a broad index fund both hold large US companies. Over one ten year stretch the index returns 11 percent a year and the value fund returns 7 percent. On 100,000 that is about 284,000 versus 197,000, a gap of 87,000 even though nothing about the strategy broke.

Illustrative example. The amounts here are hypothetical, chosen to show how the math works, not real quoted rates or figures.

03What this is NOT

04Receipts

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