‘Consumers’ considers several concepts involved with, or influenced by, consumer activity and consumer choice — substitution, complements, demand curves, income effect, statistical estimation, cost-of-living indexes, the babysitter effect, time, budgets, opportunity cost, and risk and loss aversion. What thought processes are involved in budgeting decisions? Are consumers rational? The new view of ‘behavioural economics’ suggests not and is supported by Daniel Kahneman's work that proposes two different systems of decision-making in the brain — fast and slow. The effects of consumer behaviour can be significant; for example, loss-aversion and other features of decisions under risk can seriously affect the properties of financial markets.