Behavioral finance

Money Illusion and Inflation in Investing The tendency to evaluate returns in nominal terms rather than real terms, causing investors to ignore purchasing power erosion.

Mutual Fund and ETF Flows as Sentiment Indicators Weekly mutual fund and ETF flows into equities versus bonds measure retail investor mood. Extreme inflows and outflows have historically preceded market turns.

Myopic Loss Aversion The tendency to avoid equities because frequent performance evaluation amplifies the pain of short-term losses.

Myopic Loss Aversion and Long-Term Investing Myopic loss aversion explains why frequent portfolio monitoring makes short-term losses loom larger, depressing equity allocation and long-term returns.

Narrative Bias How compelling stories cause investors to overweight qualitative information and distort portfolio decisions.

Narrative fallacy Narrative fallacy is the tendency to believe a compelling story over statistical evidence, assigning high confidence to narratives and overlooking the role of chance.

Narrative Fallacy in Investing Creating false causal stories to explain random market movements, imposing order on noise.

Narrative Fallacy in Markets Tendency to construct post-hoc explanations for price movements that feel intuitive but lack causal rigor.

Narrow framing Narrow framing is the tendency to evaluate decisions, risks, or outcomes in isolation rather than considering their broader context or impact on the overall portfolio or life situation.

Narrow Framing and Loss Aversion in Portfolio Thinking How narrow framing amplifies loss aversion by evaluating each position separately—and why viewing a portfolio as one unit reduces emotional distortion.

Neglect of Probability How investors treat low-probability events as impossible and high-impact risks as certain, distorting expected-value calculations.

Neglected Firm Effect Neglected firm effect: stocks with low analyst coverage and media attention earn higher risk-adjusted returns. A behavioral anomaly explained.

Net Stock Issuance Anomaly The net stock issuance anomaly shows that firms issuing large amounts of new equity underperform firms that buy back shares, reflecting systematic overoptimism.

Noise Trader Contagion The spread of sentiment-driven trading across uncorrelated securities or markets when investors misinterpret price moves as signals of fundamental value.

Noise Trader Risk A theoretical framework showing how irrational investor sentiment can persist, generate profits for noise traders, and push prices away from fundamentals indefinitely.

Nominal Loss Aversion How investors fixate on the nominal purchase price rather than inflation-adjusted real value, distorting hold-or-sell decisions and inflating opportunity costs.

Normalcy Bias The cognitive tendency to underestimate the likelihood and severity of financial crises and market disruptions by extrapolating stable recent conditions indefinitely into the future.

Omission bias Omission bias is the tendency to avoid taking action when action is needed, preferring to let things stay as they are rather than actively change course, even when change would be beneficial.

Optimism bias Optimism bias is the tendency to overestimate the likelihood of positive outcomes and underestimate the likelihood of negative outcomes, leading to overconfident forecasts and underestimated risks.

Optimism Bias and Investor Return Expectations Why individual investors consistently expect their own portfolios to outperform the market, even after accounting for fees and historical averages.

Option Listing Effect on Stock Volatility How stock volatility and return patterns shift measurably after options begin trading on a stock, revealing the role of options markets in price discovery.

Options Open Interest as a Sentiment Gauge Options open interest as a sentiment indicator: how traders' positioning across strike prices reveals market expectations.

Options Skew and Investor Fear Options skew measures how much investors pay for downside protection via out-of-the-money puts versus upside calls, revealing collective anxiety.

Ostrich Effect How investors avoid checking portfolio values during downturns to escape negative emotional feedback and regain control.

Outcome Bias How investors judge the quality of past decisions by results rather than by reasoning, distorting what they learn.

Overconfidence bias Overconfidence bias is the tendency to overestimate the accuracy of your knowledge, the reliability of your information, and your ability to predict the future or outperform the market.

Overconfidence Bias and Excessive Trading How overconfidence bias and excessive trading lead to inflated forecasting ability, higher turnover costs, and underperformance.

Overconfidence in Investing Systematic overestimation of one's own skill, information edge, and ability to beat the market.

Overtrading Bias Excessive trading driven by illusion of control and overconfidence in one's ability to time markets.

Pain of Paying Why handing over cash stings more than swiping a card, and how payment friction shapes spending and saving.

Pain of Regret in Trading How anticipating post-decision regret distorts buy and sell timing beyond simple loss aversion.

Panic Buying Behavior Fear-driven simultaneous purchasing of an asset irrespective of underlying value, often disconnected from rational utility.

Paper Loss Aversion Why investors feel disproportionate emotional distress from unrealized losses that outweighs the psychological impact of equivalent realized losses.

Passive Investing Crowding Risk How passive investing crowding risk concentrates index fund assets in the same large-cap stocks, potentially creating systemic fragility.

Paying Off Student Loans vs Investing: A Mental Accounting Trap How mental accounting distorts the student loan payoff vs investing decision, leading borrowers to misallocate capital relative to math.

Payment Decoupling How separating the moment of payment from consumption reduces the psychological pain of spending.

Peak-end rule Peak-end rule is the tendency to judge an experience based on its peak moment and its final moment, ignoring the duration and average experience, leading to biased memory and regret.

Peak-End Rule and Investment Memory How the peak-end rule in investing causes you to judge past investment experiences by their highest and final prices, distorting future decisions.

Peer Effect Portfolio decisions influenced by colleagues, competitors, and social reference groups rather than independent analysis.

Pennies-a-Day Framing: How Reframing Cost as Daily Amounts Bypasses Mental Accounts The psychology of pennies-a-day marketing: how $365 annual cost feels trivial when reframed as $1 daily, exploiting mental accounting biases.

Pessimism bias Pessimism bias is the tendency to overestimate the likelihood of negative outcomes and underestimate the likelihood of positive outcomes, leading to excessive caution and missed opportunities.

Planning Fallacy Why people systematically underestimate the time, cost, and risk of future projects, even when past experience shows they should expect overruns.

Planning Fallacy in Financial Projections How the planning fallacy causes budgets and financial projections to systematically underestimate costs and time, affecting both personal and business finance.

Portfolio Mental Accounting The tendency to evaluate and manage multiple investments separately rather than as a unified whole.

Portfolio Rebalancing Reluctance How loss aversion causes investors to avoid selling depreciated holdings needed to restore their target asset allocation.

Post-Earnings Announcement Drift The tendency for stocks to continue moving in the direction of an earnings surprise long after the announcement, suggesting slow information absorption.

Post-Earnings Surprise Drift The slow market reaction to earnings surprises, creating momentum opportunities as prices gradually adjust.

Pre-Holiday Drift in Stock Returns Pre-holiday stock market drift is the tendency for equity prices to drift upward in the final trading session before major holidays, driven by sentiment and reduced hedging.

Present Bias and Retirement Savings How present bias causes people to under-save for retirement despite knowing they need to, and how commitment devices can counter it.

Price Anchoring Cognitive bias where investors or consumers rely excessively on an initial piece of price information when making valuation decisions.

Price Delay Anomaly and Information Diffusion The price delay anomaly: stocks that slowly incorporate market-wide information earn higher subsequent returns, a premium for limited investor attention.

Profitability Anomaly: Why Profitable Firms Outperform Profitability anomaly: highly profitable firms earn higher returns than theory predicts. Gross profit margin as a quality screen explained.

Projection Bias in Financial Planning How investors project their current emotional state or market conditions into long-term forecasts, leading to over-commitment in booms and under-saving in busts.

Proportional Thinking Bias in Large Purchases The tendency to focus on percentage savings rather than absolute value, causing irrational decisions on large purchases and minor spending.

Prospect theory Prospect theory is the leading descriptive model of how people actually make decisions under uncertainty, incorporating loss aversion, nonlinear probability weighting, and reference dependence.

Put-Call Ratio The ratio of traded put options to call options; an options market sentiment gauge revealing real-time collective fear or complacency.

Recency and primacy effect Recency and primacy effects are the tendency to overweight recent information (recency) or initial information (primacy) when making judgments, with their relative strength depending on the context.

Recency bias Recency bias is the tendency to weigh recent events, data, or experiences much more heavily than older ones when making judgments or decisions, even when the older information is statistically more relevant.

Recency Bias in Investing Recency bias in investing leads investors to over-weight recent market events and chase past winners, ignoring longer-term patterns and fundamentals.

Recency Bias in Trading The tendency to overweight recent price performance when making trading decisions, extrapolating short-term trends.