This scenario is used in the opening of a famous paper about “mental accounting”, or the way people tend to separate money into separate “buckets” for food, shelter, transport and other expenses.
Mental accounting goes against the idea that one euro or dollar or pound is identical to another, known as “fungibility”, and explains why people might feel they can splurge in certain circumstances and not in others.
It has widespread implications for the way individuals budget and manage money (as well as the way stores price and market products).
But I’d never spend that much on a meal
In the 1980s, research by Richard Thaler, who coined the term and later went on to co-author influential book Nudge, explained that because the couple in the anecdote got the $300 financial windfall in the “food” category, they felt comfortable spending it on a lavish dinner, as it also in the food category. He writes: “The extravagant dinner would not have occurred had each couple received a yearly salary increase of $150, even though that could have been worth more in present value terms.”
Another example involves a couple earning 10% interest on money they have saved as a holiday house deposit but who also borrowed a smaller amount at 15% interest to buy a car. It is a “violation of fungibility (at obvious economic costs)” because they are effectively paying to borrow for the car despite having money saved for the house.
Mental accounting is used widely but only about a third in an eZonomics poll knew what it was and how it related to managing money.
Use your buckets wisely
This tendency to divide money into separate buckets has implications for individuals and their budgeting.
Research summarised on the Brown University website explains how mental accounting can have big influences on household spending. Examining petrol price rises, associate professor of economics Justine Hastings wrote that people typically changed petrol buying habits when prices went up rather than cutting back in a different area of spending, such as food. She writes that an equivalent fall in household income had a much smaller small effect on petrol buying habits – which is consistent with the mental accounting idea.
“A clear pattern emerged,” the research said of petrol price rises. “People behaved as if they were much poorer, buying cheaper gasoline as if a $2 increase in gasoline prices had decreased their annual income by tens of thousands of dollars.”
The full research paper is here.
Mental accounting can help – and hinder
In his 2011 book Thinking, Fast and Slow, Nobel Prize recipient Daniel Kahneman writes that mental accounting can be used as a shorthand way to control spending. Like Thaler’s couple who borrowed to fund a car (despite having the money saved in a holiday home fund), the method may be a way to limit spending on indulgences, such as barista-made coffee or to limit building debt on credit cards.
However, the petrol price research tells us that if prices of products rise noticeably, it might pay to revise the household budget as a whole. It might be that savings can be made in other areas – and money moved from one “bucket” to another – to help ease the pain of the price hikes.