Behavioural finance
Also written Behavioral finance
The 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.
In plain language
Standard finance pictures an investor who is perfectly rational, has all the information and never lets feelings get in the way. Real investors are not like that — and the workbook says so plainly: real-life investors are very different from those in standard finance theory.
Behavioural finance is the study of how psychology influences the behaviour of market participants, both at the individual and group level, and the effect this has on financial markets. It is a part of behavioural economics, which deals with biases and cognitive errors affecting investing behaviour.
Its purpose, in the workbook's words, is to explain the gaps and market anomalies that standard finance theories and frameworks do not explain. The Nobel laureates Daniel Kahneman (2002) and Richard Thaler (2017) are credited with bringing it to the forefront and trying to integrate it with standard finance.
How it works
What standard finance assumes (Chapter 14, section 14.1). Investors are:
- rational;
- risk averse;
- self-interested utility maximisers;
- updating their beliefs as new information comes in;
- with access to all available information.
What the workbook says investors actually do.
- Hold concentrated portfolios instead of diversifying.
- Show greed and fear over time instead of a rational risk-return choice.
- Attribute lucky wins to their own skill.
- Confuse a good company with a good stock.
- Prefer domestic companies because familiarity makes them feel less risky (home bias).
Table 14.1 in short.
| Standard finance | Behavioural finance |
|---|---|
| Economics at the core | Psychology at the core |
| Rational investors; EMH describes random price movement | Biases guide investments; herd mentality causes sharp moves |
| Rule-driven, consistent decisions | Inconsistent decisions — experience, recency, loss aversion |
| Risk-return trade-off is the foundation | Loss aversion is the basis |
| Detailed analysis | Ad hoc thumb rules |
The toolkit. How people decide: bounded rationality (Herbert Simon) and prospect theory (Kahneman and Tversky, 1979). What goes wrong: emotional biases (loss aversion, overconfidence, endowment, status quo) and cognitive errors (mental accounting, framing, anchoring). What it explains: anomalies, bubbles and crashes.
A worked example
Illustrative figures. Suresh, 45, has ₹50 lakh in financial assets. A standard-finance model predicts a diversified portfolio matched to his risk tolerance. His actual portfolio:
| Holding | Amount | Share | What behavioural finance calls it |
|---|---|---|---|
| Shares of his employer | ₹20 lakh | 40% | Concentration; familiarity |
| Three small-caps that doubled last year | ₹15 lakh | 30% | Attributing a bull-market win to skill |
| A stock bought at ₹900, now ₹450 | ₹5 lakh | 10% | Holding a loser — loss aversion |
| Fixed deposits | ₹10 lakh | 20% | — |
| Total | ₹50 lakh | 100% |
Check: 20 + 15 + 5 + 10 = ₹50 lakh.
Standard finance can only call this irrational. Behavioural finance names each pattern and predicts it. That is why the workbook places psychographic analysis in the portfolio management process (Chapter 9): a manager who knows Suresh's biases can write an investment policy statement that guards against them — for example, a cap on any single holding.
Why NISM asks about it
Chapter 14 (Behavioural Finance) is worth 5 marks in the XXI-B syllabus outline. Section 14.1 contrasts behavioural and standard finance; sections 14.2–14.5 cover decision-making, biases, fusion investing, anomalies and bubbles. Chapter 14's sample question 5 asks how behavioural finance differs from the standard model — answer: it includes the impact of investor psychology. Chapter 9 (section 9.3.8) uses the same contrast to explain why psychographic analysis matters, and Chapter 13 covers the market anomalies that behavioural finance tries to explain.
Common exam traps
- Behavioural finance includes investor psychology; it does not preclude it, does not accept the EMH as a given and does not reject anomalies — those are the sample question's wrong options.
- It is a part of behavioural economics, not the other way round.
- Kahneman 2002 and Thaler 2017 are Nobel years. Prospect theory itself is dated 1979; bounded rationality is credited to Herbert Simon (1978).
- Standard finance also assumes investors are risk averse. Risk aversion is not a behavioural bias; loss aversion is.
- Emotional bias does not mean making errors in the workbook's framing — it has a protective side. Cognitive errors are the faulty-reasoning family.
Where this is taught
- Series XXI-B · Chapter 14: Behavioural Financeintroduced here
- Series X-B · Chapter 16: Basics of Behavioral Financeintroduced here
Related terms
- 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.
- Bounded rationalityHerbert Simon's idea that people with limited time, information and processing ability settle for a satisfactory and sufficient choice — they 'satisfice' — instead of finding the optimal one.
- Market anomalyA 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.
- Overconfidence biasAn emotional bias in which people place unwarranted faith in their own judgement and abilities — leading to underestimated risk, concentrated portfolios and excessive trading.
- Prospect theoryKahneman and Tversky's 1979 theory of choice under risk: outcomes are judged as gains or losses from a reference point, and losses hurt more than equal gains please.
- Psychographic analysisProfiling an investor's personality and behavioural traits to set the risk profile — treating the investor as a normal human prone to bias rather than a purely rational actor.
- Mental accountingA cognitive error in which people treat equal sums of money differently depending on where they came from or what they are earmarked for, instead of treating all money as interchangeable.
- Status quo biasAn emotional bias in which a person, fearing regret, ends up taking no decision at all and keeps things as they are — closely linked to regret aversion.
- Framing biasA cognitive error in which a person answers the same question differently depending on how it is presented — for example, "0% fat" versus "100% fat free".
- Endowment biasAn emotional bias in which people value an asset more simply because they own it — its two attributes are valuing ownership and loss aversion.
- Fusion investingA strategy that combines fundamental analysis with behavioural finance: screen for value, filter for financial strength, then pick the stocks showing strong price momentum.
- 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.
- Risk averse investorAn investor who accepts risk only when paid a positive expected risk premium for it, and who demands a larger premium the greater the risk.
- NudgeA small, low-cost change in how a choice is presented — not a mandate or a financial incentive — that steers investors toward a better decision by working with a behavioural bias instead of against it.
- 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.
- BB&K modelA psychographic framework that sorts investors into five personality types — Adventurer, Celebrity, Individualist, Guardian and Straight Arrow — using confidence and carefulness as its two axes.
- Emotional biasOne of two investing bias categories in behavioural finance — spontaneous decisions driven by deep-rooted feeling, as opposed to cognitive errors, which come from faulty reasoning.
- Standard financeThe traditional view of finance built on rational, self-interested investors with full information — the baseline set of assumptions that behavioural finance was developed to challenge.
- Stereotyping biasAn emotional bias in which investors judge an investment by a general, surface-level impression instead of its actual merits — such as assuming a high-profile manager guarantees a well-run company.
- Illusion of controlThe belief that familiarity, information access or active involvement gives an investor influence over a price — which leads to a conviction that he can forecast it and sell out before everybody else.
- AnchoringA behavioural bias where an investor clings to a piece of information — often a past price — and keeps basing decisions on it even after it has stopped being relevant.