Market anomaly
Also written Capital market anomaly · Market anomalies
A pattern of returns that departs from what an asset's fundamentals and risk — as measured by CAPM or another pricing model — say it should earn, and so contradicts market efficiency.
In plain language
Imagine markets were fully efficient. Imagine CAPM, the standard model of risk and return, measured risk perfectly. Then every stock would earn just the return its risk deserves, plus or minus random noise.
A market anomaly is a lasting exception you can see to that picture.
The workbook defines it in two ways:
- Chapter 13: market behaviour that does not fit the existing models of risk and return. It is also a challenge to the efficient market hypothesis.
- Chapter 14: a stock's price moving away from the value its fundamentals suggest. It is a price change that current, relevant news cannot explain. Here, actual returns differ from the expected return that CAPM or other models call for.
Anomalies are where active managers hunt for alpha, which means returns above what the risk would predict. Several popular investment strategies grew straight out of them.
How it works
Anomalies in Chapter 13
| Anomaly | What was observed | Strategy it fed |
|---|---|---|
| January effect | In the US, tax-loss selling pushes prices down in November–December and up in early January | Buying in December, selling in January |
| Size anomaly | Small firms consistently earned larger risk-adjusted returns than large firms | Small-cap portfolios |
| Value anomaly | High book-to-price stocks generated superior risk-adjusted returns | Value investing |
The US tax authority responded to the January pattern with wash sale rules: a loss is not deductible if substantially identical securities are bought within 30 days before or after the sale.
The behavioural explanation (Chapter 14). Biases make investors err systematically, and systematic errors create anomalies. Overconfidence leads to underestimating risk; self-attribution bias leads investors to follow confirming information and trade too often; the disposition effect — holding losers, selling winners early — explains momentum in prices.
The workbook's summary of their life cycle: anomalies appear, disappear and reappear quite randomly. Some vanish as others exploit them; some persist for much longer.
A worked example
Illustrative figures, using the workbook's Security Market Line inputs. A portfolio manager builds a ₹10 lakh basket of high book-to-price mid-cap stocks. The basket's beta is 1.2, the risk-free rate is 8% and the market risk premium is 14%.
CAPM required return = 8% + 1.2 × 14% = 24.8%
Required gain on ₹10 lakh = ₹2,48,000
Over the year the basket actually returns 30%, or ₹3,00,000.
The gap of 5.2% — ₹52,000 — is not explained by the basket's market risk. If it were a one-off, it would be noise. If baskets built the same way beat their CAPM-required returns year after year, across many samples, that persistent gap is the value anomaly, and it is evidence against semi-strong efficiency (book-to-price is public information).
The manager should still ask the workbook's questions: does the anomaly survive transaction costs? Is it likely to disappear as more managers chase it? And is the model's measure of risk — a single beta — missing something that the "excess" is actually paying for?
Why NISM asks about it
Chapter 13 (Concept of Informational Efficiency), section 13.4, covers the January, size and value anomalies; a sample question calls the year-end tax-selling pattern the January Anomaly. Chapter 14 (Behavioural Finance), section 14.5.1, defines anomalies against CAPM-expected returns and explains them through biases. Chapter 18 builds strategies — small-cap, value, momentum, fusion investing — on these same anomalies.
Common exam traps
- An anomaly is measured on a risk-adjusted basis. Small caps earning more is not an anomaly by itself; earning more after adjusting for risk is.
- The January effect is from the US market and rests on US tax-loss selling — the workbook presents it that way.
- Value anomaly = high book-to-price (equivalently, low price-to-book), not high P/E.
- Wash sale window: 30 days before or after the loss sale.
- Momentum is explained by the disposition effect in the workbook — investors selling winners too early and holding losers too long.
- Anomalies can disappear, persist, or reappear — the workbook does not treat them as permanent.
Where this is taught
Free preparation for NISM Series XXI-BRelated terms
- CAPMA model that prices the return an investor should demand from a share: the risk-free rate plus beta times the market risk premium.
- Efficient Market HypothesisThe proposition that share prices already incorporate and reflect all relevant information — which, if true, leaves nothing for an analyst to find by studying that information.
- AlphaThe return a fund earned above what its beta and the benchmark say it should have earned — the slice of performance left over once the market has been given credit for its share.
- Disposition effectInvestors' tendency to sell winning investments too early and hold losing ones too long — named by Shefrin and Statman (1985) and rooted in loss aversion.
- Semi-strong-form EfficiencyThe hypothesis that prices reflect all historical and publicly available information and adjust rapidly to news — so neither technical nor fundamental analysis earns above-average risk-adjusted returns.
- Weak-form EfficiencyThe hypothesis that current prices already reflect all historical market information — past prices, returns and volumes — so technical analysis cannot earn above-average risk-adjusted returns.
- Strong-form EfficiencyThe most extreme form of the efficient market hypothesis: prices reflect all historical, public and insider information, so no group of investors can earn above-average risk-adjusted returns.
- Behavioural financeThe study of how psychology shapes the decisions of market participants, individually and in groups, and how those decisions show up as gaps and anomalies in financial markets.
- BubbleIn Kindleberger's description, a sharp, continuous rise in an asset's price in which early gains create expectations of further rises and draw in speculators seeking trading profits.
- Informational EfficiencyHow fully and quickly security prices reflect available information. It is what "market efficiency" usually means, as against operational efficiency, which is about transaction costs.
- Size AnomalyThe finding that small firms, measured by total market value, have consistently earned larger risk-adjusted returns than large firms — contradicting market efficiency.
- Value AnomalyThe finding that stocks with a high book value-to-price ratio have earned superior risk-adjusted returns — an anomaly against the EMH that underpins value investing.
- Self-attribution biasThe tendency to credit one's own skill for investment successes while blaming bad luck or others for failures — a bias that intensifies overconfidence and filters out information that contradicts it.
- Fair Game ModelEugene Fama's 1970 framing of the efficient market hypothesis: current price fully reflects available information, so no investment strategy can consistently earn above-average risk-adjusted returns.
- Wash SaleA US tax rule, cited by the workbook to explain the January Effect: it disallows a loss deduction when an investor sells a security at a loss and buys back a substantially identical one within 30 days before or after.
- Undervalued securityUnder CAPM, a security whose estimated return plots above the Security Market Line — earning more than its systematic risk (beta) warrants under market equilibrium.
- Momentum investingAn active strategy that rides an ongoing price trend — long in a rising trend, short in a falling one — worked from price and volume data rather than a company's fundamentals.
- January effectA market anomaly in the US: year-end tax selling pushes prices down in late November and December, and the buying back in early January pushes them up — a pattern inconsistent with market efficiency.
- Unbiased EstimateThe technical definition of an efficient market price: the market price is an unbiased estimate of a security's true value, so deviations are random rather than one-sided.