Rational expectations

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Rational expectations is an economic theory that seeks to infer the macroeconomic consequences of individuals' decisions based on all available knowledge. It assumes that individuals actions are based on the best available economic theory and information, and concludes that government policies cannot succeed by assuming widespread systematic error by individuals.



The concept of rational expectations was first introduced by John F. Muth in his paper "Rational Expectations and the Theory of Price Movements" published in 1961. Robert Lucas and Thomas Sargent further developed the theory in the 1970s and 1980s which became seminal works on the topic and were widely used in microeconomics. [1]

Significant Findings

Muth’s work introduces the concept of rational expectations and discusses its implications for economic theory. He argues that individuals are rational and use all available information to make unbiased, informed predictions about the future. This means that individuals do not make systematic errors in their predictions and that their predictions are not biased by past errors. Muth’s paper also discusses the implication of rational expectations for economic theory. One key implication is that government policies, such as changes in monetary or fiscal policy may not be as effective if individuals’ expectations are not considered. For example, if individuals expect inflation to increase, they may anticipate that the central bank will raise interest rates to combat inflation, which could lead to higher borrowing costs and slower economic growth. Similarly, if individuals expect a recession, they may reduce their spending and investment, which could lead to a self-fulling prophecy. [2]

Lucas’ paper “Expectations and the Neutrality of Money” expands on Muth's work and sheds light on the relationship between rational expectations and the monetary policy. The paper argues that when individuals hold rational expectations, changes in the money supply do not have real effects on the economy and the neutrality of money holds. Lucas presents a theoretical model that incorporates rational expectations into an analysis of the effects of changes in the money supply. The model suggests that individuals adjust their expectations in response to changes in the money supply, which eliminates the effect on real variables such as output and employment. He argues that a stable monetary policy that is consistent with individuals' rational expectations will be more effective in promoting economic stability than attempts to manipulate the money supply. [3]

In 1973, Thomas J Sargent published the article “Rational Expectations, the Real Rate of Interest, and the Natural Rate of Unemployment” which was an important contribution to the development and application of the concept of rational expectations in economic theory and policy. By assuming individuals are forward-looking and rational, Sargent argues that rational expectations can help explain fluctuations in key economic variables such as the real interest rate and the natural rate of employment. He also suggests that the concept of the natural rate of unemployment can be used to help policymakers set macroeconomic policy. This concept suggests that there is a trade-off between unemployment and inflation in the short run, but in the long run, the economy will return to the natural rate of unemployment, which is determined by structural factors such as the skills of the labour force and the efficiency of the labour market. Sargent argues that policymakers should take this concept into account when setting macroeconomic policy, as policies that try to push unemployment below the natural rate will only lead to higher inflation in the long run. [4]


The key idea of rational expectations is that individuals make decisions based on all available information, including their own expectations about future events. This implies that individuals are rational and use all available information to make decisions. Another important idea is that individuals adjust their expectations in response to new information. In this way, individuals are assumed to be forward-looking and able to adapt to changing circumstances. They will learn from past trends and experiences to make their best guess of the future. [1]

It is assumed that an individual's predicted outcome do not differ systematically from the market equilibrium given that they do not make systematic errors when predicting the future.

In an economic model, this is typically modelled by assuming that the expected value of a variable is equal to the expected value predicted by the model. For example, suppose that P is the equilibrium price in a simple market, determined by supply and demand. The theory of rational expectations implies that the actual price will only deviate from the expectation if there is an 'information shock' caused by information unforeseeable at the time expectations were formed. In other words, ex ante the price is anticipated to equal its rational expectation:

where is the rational expectation and is the random error term, which has an expected value of zero, and is independent of .

Mathematical derivation

If rational expectations are applied to the Phillips curve analysis, the distinction between long and short term will be completely negated, that is, there is no Phillips curve, and there is no substitute relationship between inflation rate and unemployment rate that can be utilized.

The mathematical derivation is as follows:

Rational expectation is consistent with objective mathematical expectation:

Mathematical derivation (1)

Assuming that the actual process is known, the rate of inflation depends on previous monetary changes and changes in short-term variables such as X (for example, oil prices):



(3) ,



Thus, even in the short run, there is no substitute relationship between inflation and unemployment. Random shocks, which are completely unpredictable, are the only reason why the unemployment rate deviates from the natural rate.

Mathematical derivation (2)

Even if the actual rate of inflation is dependent on current monetary changes, the public can make rational expectations as long as they know how monetary policy is being decided:






The conclusion is essentially the same: random shocks that are completely unpredictable are the only thing that can cause the unemployment rate to deviate from the natural rate.


Rational expectations theories were developed in response to perceived flaws in theories based on adaptive expectations. Under adaptive expectations, expectations of the future value of an economic variable are based on past values. For example, it assumes that individuals predict inflation by looking at historical inflation data. Under adaptive expectations, if the economy suffers from a prolonged period of rising inflation, people are assumed to always underestimate inflation. Many economists suggested that it was an unrealistic and irrational assumption, as they believe that rational individuals will learn from past experiences and trends and adjust their predictions accordingly.

The rational expectations hypothesis has been used to support conclusions about economic policymaking. An example is the policy ineffectiveness proposition developed by Thomas Sargent and Neil Wallace. If the Federal Reserve attempts to lower unemployment through expansionary monetary policy, economic agents will anticipate the effects of the change of policy and raise their expectations of future inflation accordingly. This will counteract the expansionary effect of the increased money supply, suggesting that the government can only increase the inflation rate but not employment.

If agents do not form rational expectations or if prices are not completely flexible, discretional and completely anticipated, economic policy actions can trigger real changes. [5]


While the rational expectations theory has been widely influential in macroeconomic analysis, it has also been subject to criticism:

Unrealistic assumptions: The theory assumes that individuals have perfect information and can process it without error. This is unlikely to be the case, due to limited information available and human error. [6]

Limited empirical support: While there is some evidence that individuals do incorporate expectations into their decision-making, it is unclear whether they do so in the way predicted by the rational expectations theory. [6]

Misspecification of models: The rational expectations theory assumes that individuals have a common understanding of the model used to make predictions. However, if the model is misspecified, this can lead to incorrect predictions. [7]

Inability to explain certain phenomena: The theory is also criticised for its inability to explain certain phenomena, such as bubbles and crashes in financial markets. [8]

Lack of attention to distributional effects: Critics argue that the rational expectations theory focuses too much on aggregate outcomes and does not pay enough attention to the distributional effects of economic policies. [6]

See also


  1. 1 2 "Rational Expectations". Corporate Finance Institute. Retrieved 2023-04-25.
  2. Muth, John.F (1961). "Rational expectations and the theory of price movements".
  3. Lucas, R.E (1970). "Expectations and the Neutrality of Money" (PDF).
  4. Sargent, T.J (1973). "Rational Expectations, the Real Rate of Interest, and the Natural Rate of Unemployment" (PDF).
  5. Galbács, Peter (2015). The Theory of New Classical Macroeconomics. A Positive Critique. Contributions to Economics. Heidelberg/New York/Dordrecht/London: Springer. doi:10.1007/978-3-319-17578-2. ISBN   978-3-319-17578-2.
  6. 1 2 3 Mankiw, N.G (2006). "The Macroeconomist as Scientist and Engineer".
  7. Romer, David (2000). "Keynesian Macroeconomics without the LM Curve".
  8. Shiller, R.J (1980). "Do stock prices move too much to be justified by subsequent changes in dividends?" (PDF).

Related Research Articles

In economics, adaptive expectations is a hypothesized process by which people form their expectations about what will happen in the future based on what has happened in the past. For example, if people want to create an expectation of the inflation rate in the future, they can refer to past inflation rates to infer some consistencies and could derive a more accurate expectation the more years they consider.

<span class="mw-page-title-main">Macroeconomics</span> Study of an economy as a whole

Macroeconomics is a branch of economics that deals with the performance, structure, behavior, and decision-making of an economy as a whole. This includes regional, national, and global economies. Macroeconomists study topics such as output/GDP and national income, unemployment, price indices and inflation, consumption, saving, investment, energy, international trade, and international finance.

<span class="mw-page-title-main">Inflation</span> Devaluation of currency over a period of time

In economics, inflation is a general increase in the prices of goods and services in an economy. This is usually measured using the consumer price index (CPI). When the general price level rises, each unit of currency buys fewer goods and services; consequently, inflation corresponds to a reduction in the purchasing power of money. The opposite of CPI inflation is deflation, a decrease in the general price level of goods and services. The common measure of inflation is the inflation rate, the annualized percentage change in a general price index. As prices faced by households do not all increase at the same rate, the consumer price index (CPI) is often used for this purpose.

New Keynesian economics is a school of macroeconomics that strives to provide microeconomic foundations for Keynesian economics. It developed partly as a response to criticisms of Keynesian macroeconomics by adherents of new classical macroeconomics.

The Phillips curve is an economic model, named after Bill Phillips, that correlates reduced unemployment with increasing wages in an economy. While Phillips did not directly link employment and inflation, this was a trivial deduction from his statistical findings. Paul Samuelson and Robert Solow made the connection explicit and subsequently Milton Friedman and Edmund Phelps put the theoretical structure in place.

A macroeconomic model is an analytical tool designed to describe the operation of the problems of economy of a country or a region. These models are usually designed to examine the comparative statics and dynamics of aggregate quantities such as the total amount of goods and services produced, total income earned, the level of employment of productive resources, and the level of prices.

Neutrality of money is the idea that a change in the stock of money affects only nominal variables in the economy such as prices, wages, and exchange rates, with no effect on real variables, like employment, real GDP, and real consumption. Neutrality of money is an important idea in classical economics and is related to the classical dichotomy. It implies that the central bank does not affect the real economy by creating money. Instead, any increase in the supply of money would be offset by a proportional rise in prices and wages. This assumption underlies some mainstream macroeconomic models. Others like monetarism view money as being neutral only in the long run.

<span class="mw-page-title-main">John B. Taylor</span> American economist (born 1946).

John Brian Taylor is the Mary and Robert Raymond Professor of Economics at Stanford University, and the George P. Shultz Senior Fellow in Economics at Stanford University's Hoover Institution.

<span class="mw-page-title-main">Thomas J. Sargent</span> American economist

Thomas John Sargent is an American economist and the W.R. Berkley Professor of Economics and Business at New York University. He specializes in the fields of macroeconomics, monetary economics, and time series econometrics. As of 2020, he ranks as the 29th most cited economist in the world. He was awarded the Nobel Memorial Prize in Economics in 2011 together with Christopher A. Sims for their "empirical research on cause and effect in the macroeconomy".

<span class="mw-page-title-main">Edmund Phelps</span> American economist

Edmund Strother Phelps is an American economist and the recipient of the 2006 Nobel Memorial Prize in Economic Sciences.

The policy-ineffectiveness proposition (PIP) is a new classical theory proposed in 1975 by Thomas J. Sargent and Neil Wallace based upon the theory of rational expectations, which posits that monetary policy cannot systematically manage the levels of output and employment in the economy.

The Lucas islands model is an economic model of the link between money supply and price and output changes in a simplified economy using rational expectations. It delivered a new classical explanation of the Phillips curve relationship between unemployment and inflation. The model was formulated by Robert Lucas, Jr. in a series of papers in the 1970s.

The neoclassical synthesis (NCS), neoclassical–Keynesian synthesis, or just neo-Keynesianism was a neoclassical economics academic movement and paradigm in economics that worked towards reconciling the macroeconomic thought of John Maynard Keynes in his book The General Theory of Employment, Interest and Money (1936). It was formulated most notably by John Hicks (1937), Franco Modigliani (1944), and Paul Samuelson (1948), who dominated economics in the post-war period and formed the mainstream of macroeconomic thought in the 1950s, 60s, and 70s.

New classical macroeconomics, sometimes simply called new classical economics, is a school of thought in macroeconomics that builds its analysis entirely on a neoclassical framework. Specifically, it emphasizes the importance of rigorous foundations based on microeconomics, especially rational expectations.

Non-accelerating inflation rate of unemployment (NAIRU) is a theoretical level of unemployment below which inflation would be expected to rise. It was first introduced as NIRU by Franco Modigliani and Lucas Papademos in 1975, as an improvement over the "natural rate of unemployment" concept, which was proposed earlier by Milton Friedman.

<span class="mw-page-title-main">History of macroeconomic thought</span>

Macroeconomic theory has its origins in the study of business cycles and monetary theory. In general, early theorists believed monetary factors could not affect real factors such as real output. John Maynard Keynes attacked some of these "classical" theories and produced a general theory that described the whole economy in terms of aggregates rather than individual, microeconomic parts. Attempting to explain unemployment and recessions, he noticed the tendency for people and businesses to hoard cash and avoid investment during a recession. He argued that this invalidated the assumptions of classical economists who thought that markets always clear, leaving no surplus of goods and no willing labor left idle.

In monetary policy, the McCallum rule specifies a target for the monetary base (M0) which could be used by a central bank. The McCallum rule was proposed by Bennett T. McCallum at Carnegie Mellon University's Tepper School of Business. It is an alternative to the well known Taylor rule and performs better during crisis periods.

The random walk model of consumption was introduced by economist Robert Hall. This model uses the Euler numerical method to model consumption. He created his consumption theory in response to the Lucas critique. Using Euler equations to model the random walk of consumption has become the dominant approach to modeling consumption.

The Lucas aggregate supply function or Lucas "surprise" supply function, based on the Lucas imperfect information model, is a representation of aggregate supply based on the work of new classical economist Robert Lucas. The model states that economic output is a function of money or price "surprise". The model accounts for the empirically based trade off between output and prices represented by the Phillips curve, but the function breaks from the Phillips curve since only unanticipated price level changes lead to changes in output. The model accounts for empirically observed short-run correlations between output and prices, but maintains the neutrality of money in the long-run. The policy ineffectiveness proposition extends the model by arguing that, since people with rational expectations cannot be systematically surprised by monetary policy, monetary policy cannot be used to systematically influence the economy.

The Taylor contract or staggered contract was first formulated by John B. Taylor in his two articles, in 1979 "Staggered wage setting in a macro model". and in 1980 "Aggregate Dynamics and Staggered Contracts". In its simplest form, one can think of two equal sized unions who set wages in an industry. Each period, one of the unions sets the nominal wage for two periods. This means that in any one period, only one of the unions can reset its wage and react to events that have just happened. When the union sets its wage, it sets it for a known and fixed period of time. Whilst it will know what is happening in the first period when it sets the new wage, it will have to form expectations about the factors in the second period that determine the optimal wage to set. Although the model was first used to model wage setting, in new Keynesian models that followed it was also used to model price-setting by firms.