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Behavioural Economics: Cognitive Biases and Bounded Rationality
IB DP Economics — Unit 2: Microeconomics | HL | 2.4 Critique of the Maximising Behaviour of Consumers and Producers
📋 What You Will Learn
- Explain the concept of bounded rationality and why it challenges the standard economic model of rational decision-making
- Identify and explain the key cognitive biases: rule-of-thumb heuristics, anchoring, framing, availability bias, and overconfidence bias
- Explain how firms exploit cognitive biases in pricing, marketing, and product design
- Analyse the implications of bounded rationality for consumer welfare and market outcomes
- Evaluate the effectiveness of nudge theory and choice architecture as policy responses to irrational behaviour
- Apply behavioural economics concepts to real-world examples and IB Paper 1 and Paper 2 questions
🔍 Guiding Question If consumers and producers do not always act rationally, what are the implications for how markets function — and what, if anything, should governments do about it?
🌍 Why This Matters In 2023, Amazon's Prime Day generated over $12.9 billion in sales in 48 hours — largely driven by countdown timers, "limited stock" warnings, and prices displayed as slashed from inflated original figures. None of these tactics change the fundamental value of the goods. They change how consumers perceive value. Standard economic theory, which assumes rational maximising agents, cannot explain why these techniques work. Behavioural economics can.
The Standard Model and Its Limits
Traditional microeconomics assumes that consumers are rational utility maximisers — they have well-defined preferences, access to perfect information, and consistently choose the option that maximises their wellbeing. Producers are assumed to maximise profits. These assumptions generate clean, predictable models. But decades of experimental evidence show that real people systematically deviate from this ideal in predictable, patterned ways.
📖 Definition — Rational Economic Agent A rational economic agent is one who uses all available information to make decisions that maximise their utility (consumers) or profit (producers), consistently and without error.
The problem is not that people are occasionally irrational — it is that their irrationality is systematic and predictable. Behavioural economics, pioneered by psychologists Daniel Kahneman and Amos Tversky and later extended by Richard Thaler, documents these patterns and asks what they mean for economic outcomes.
📖 Definition — Behavioural Economics Behavioural economics is a field that incorporates insights from psychology into economic analysis to explain why individuals often make decisions that deviate from the predictions of the standard rational model.
Bounded Rationality
The concept of bounded rationality, introduced by Herbert Simon, offers a more realistic account of human decision-making. Rather than optimising perfectly, people make decisions that are "good enough" given their cognitive limitations, time constraints, and the complexity of the information available to them.
📖 Definition — Bounded Rationality Bounded rationality refers to the idea that individuals make decisions that are rational within the limits of their cognitive capacity, available information, and time — but these limits mean their choices often fall short of the perfectly rational optimum assumed by standard theory.
- Cognitive limits: the human brain cannot process all available information simultaneously — it uses shortcuts (heuristics) to simplify complex decisions
- Information constraints: even when information is available, people do not always seek it out or process it correctly
- Time constraints: decisions must often be made quickly, preventing thorough analysis
- Satisficing behaviour: rather than maximising, people often choose the first option that meets a minimum acceptable threshold — they "satisfice" rather than optimise
- Implication for markets: if consumers are boundedly rational, markets may not allocate resources efficiently even without the traditional sources of market failure (externalities, public goods, etc.)
🔗 Analogy — The Overwhelmed Shopper Imagine choosing a laptop from 200 options on an e-commerce site. A perfectly rational agent would compare every specification, calculate lifetime value, and select the utility-maximising option. In reality, most people look at the top three results, check the star rating, glance at the price, and buy. This is satisficing — and it is entirely predictable. Firms design their websites knowing this is how people behave.
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