Not Rational Utility Maximisers

One cornerstone of neoclassical economic thought is the assumption in microeconomics (and microfounded macroeconomics) that humans behave as “rational utility maximisers”.

Yet this assumption is increasingly outdated. Empirical findings in behavioural economics show that the neoclassical assumption of utility maximisation has very little basis in reality.

First, it is crucial to define what we mean by utility maximisation. Paul Samuelson, one of the grandfathers of the neoclassical New Keynesian school defined consumer rationality as follows:

• Completeness — Given any 2 bundles of commodities A & B , the consumer can decide whether he prefers A to B (A≻B), B to A (B≻A), or is indifferent between them (B≈A).

• Transitivity — If (A≻B) and (B≻C) then (A≻C).

• Non-satiation — More is preferred to less.

• Convexity — Marginal utility falls as consumption of any good rises.

This definition remains dominant in neoclassical economics today.

Sippel (1997) tested whether consumers really adhered to these four rules. He gave his student test subjects a budget, and a set of eight priced commodities to spend their budget on:


This was repeated ten times, with ten different budget and price combinations. Sippel found that 11 out of 12 of his test subjects’ behaviour failed to meet Samuelson’s criteria for rational utility maximisation. Sippel repeated the experiment later with thirty test subjects, finding that 22 out of 30 did not meet Samuelson’s criteria. Sippel concluded:

We conclude that the evidence for the utility maximisation hypothesis is at best mixed. While there are subjects who appear to be optimising, the majority of them do not.

It is interesting that some individuals obey the rules set out by Samuelson, and that some don’t. Human behaviour is highly variable from individual to individual. If the hypothesis of utility maximisation is right about a subset of individuals, but wrong about much of the general population, then this underlines the variability of human behaviour. And different circumstances call for different decision-making frameworks — some individuals may act like rational utility maximisers under some sets of circumstances and not others. This is really an area that deserves much, much more empirical study.

The evidence so far suggests that humans are complex animals whose decisions are multi-dimensional. This could be because our brains have evolved to use different neuro-circuitry for different decisions. According to the behavioural economist Daniel McFadden:

Our brains seem to operate like committees, assigning some tasks to the limbic system, others to the frontal system. The “switchboard” does not seem to achieve complete, consistent communication between different parts of the brain. Pleasure and pain are experienced in the limbic system, but not on one fixed “utility” or “self-interest” scale. Pleasure and pain have distinct neural pathways, and these pathways adapt quickly to homeostasis, with sensation coming from changes rather than levels. Overall, presumably as a product of evolution, our brains are organized well enough to keep us alive, fed, reproducing, and responsive to but not overwhelmed by sensation, but they are not hedonometers.

All of this points to the idea that microeconomics needs a new framework based on neurological and behavioural evidence, not decades-old assumptions that are unsupported by empirical evidence.

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Penis Length, LIBOR & Soviet Growth

Healthy markets require solid data based on reality.

It is hard enough to determine what, when and how to invest even with solid data. We live in an unpredictable and chaotic world, and the last thing that investors need is misinformation and distortions. That is why the LIBOR manipulation scandal is so infuriating; as banks skewed the figures, they skewed entire marketplaces. The level of economic distortion is incalculable — as LIBOR is used to price hundreds of trillions of assets, the effects cascaded across the entire financial system and the wider world. An unquantifiable number of good trades were made bad, and vice verse. Yet in truth we should not expect anything else from a self-reported system like LIBOR. Without real checks and balances to make sure that the data is sturdy, data should be treated as completely unreliable.

Unsurprisingly, it is emerging that many more self-reported figures may have been skewed by self-reporting bullshittery.

The Telegraph noted:

The Libor scandal could be repeated in a number of other “self-certifying” markets where prices are determined, he said

“Self-certification is clearly open to abuse, so this could occur elsewhere,” he said.

A Financial Services Authority inquiry into Libor should be extended to other self-certifying markets, he said. The Treasury said last night that the review, led by Martin Wheatley, was free to examine markets other than Libor.

An expansion of the FSA review could take in a number of other interest-rate-related data as well as some complex financial instruments measuring the difference between banks’ borrowing costs and that of the US government.[i.e. the Ted spread]. Some markets in gold and oil are also based on self-certification.

This all reminds me of this:

When humans have an incentive to exaggerate or lie — either to bolster their ego by lying about penis size, or to cream an easy profit by rigging rates — it seems they have a propensity to do so.

Hopefully there will be one beneficial side-effect of the LIBOR rigging — self-reporting will die. It seems inevitable that market participants will pay a premium for solid, independent data. But sadly, any auditor can be bribed. And in a generation’s time, the LIBOR-rigging scandal of 2008 (and probably much earlier) may just be an antique detail known to only a savvy few. Scepticism, caution and portfolio robustification will always remain essential tools for savvy investors who don’t want to lose their shirt and shoes.

It was scepticism that was the difference between economists who refused to buy into the notion of Soviet prosperity in spite of impressive (and entirely self-reported) figures emerging from the Soviet Union, and those Western economists like Paul Samuelson (perhaps spurred on by ideological fervour) who predicted again and again in textbooks spanning thirty years that the USSR would overtake the USA in GDP:

Alex Tabarrok notes:

In the 1961 edition of his famous textbook of economic principles, Paul Samuelson wrote that GNP in the Soviet Union was about half that in the United States but the Soviet Union was growing faster.  As a result, one could comfortably forecast that Soviet GNP would exceed that of the United States by as early as 1984 or perhaps by as late as 1997 and in any event Soviet GNP would greatly catch-up to U.S. GNP.  A poor forecast — but it gets worse because in subsequent editions Samuelson presented the same analysis again and again except the overtaking time was always pushed further into the future so by 1980 the dates were 2002 to 2012.  In subsequent editions, Samuelson provided no acknowledgment of his past failure to predict and little commentary beyond remarks about “bad weather” in the Soviet Union.

The reason for his prediction? Apparently, bad data.

“No incentive to amend data to show strong Russian proletarian outperforms weak American capitalist, Comrade!”

Matthew Ashton writes:

To his credit Samuelson was always fairly open about it when his predictions failed to come true, stating that he was using the best data available at the time and he changed his mind as the evidence changed. I’d argue that in some cases, especially concerning evidence coming out of the Soviet Union, he possibly should have been a bit more sceptical as to its accuracy, however almost everyone in economics is guilty of that.

One can only wonder how bad the state of misreporting, fraud and delusion is in the various economies where central planning plays an even larger role than here in the West.