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Real business-cycle theory

real business cycle theory, real business cycle theory emphasizes the role of
Real business-cycle theory RBC theory is a class of new classical macroeconomics models in which business-cycle fluctuations to a large extent can be accounted for by real in contrast to nominal shocks Unlike other leading theories of the business cycle,citation needed RBC theory sees business cycle fluctuations as the efficient response to exogenous changes in the real economic environment That is, the level of national output necessarily maximizes expected utility, and governments should therefore concentrate on long-run structural policy changes and not intervene through discretionary fiscal or monetary policy designed to actively smooth out economic short-term fluctuations

According to RBC theory, business cycles are therefore "real" in that they do not represent a failure of markets to clear but rather reflect the most efficient possible operation of the economy, given the structure of the economy

Real business cycle theory categorically rejects Keynesian economics and the real effectiveness of monetary policy as promoted by monetarism and New Keynesian economics, which are the pillars of mainstream macroeconomic policy

RBC theory is associated with freshwater economics the Chicago School of Economics in the neoclassical tradition


  • 1 Business cycles
  • 2 Stylized facts
    • 21 Calibration
    • 22 Structural variables
  • 3 Criticisms
  • 4 See also
  • 5 References
  • 6 Further reading

Business cyclesedit

If we were to take snapshots of an economy at different points in time, no two photos would look alike This occurs for two reasons:

  1. Many advanced economies exhibit sustained growth over time That is, snapshots taken many years apart will most likely depict higher levels of economic activity in the later period
  2. There exist seemingly random fluctuations around this growth trend Thus given two snapshots in time, predicting the latter with the earlier is nearly impossible

A common way to observe such behavior is by looking at a time series of an economy's output, more specifically gross national product GNP This is just the value of the goods and services produced by a country's businesses and workers

Figure 1 shows the time series of real GNP for the United States from 1954–2005 While we see continuous growth of output, it is not a steady increase There are times of faster growth and times of slower growth Figure 2 transforms these levels into growth rates of real GNP and extracts a smoother growth trend A common method to obtain this trend is the Hodrick–Prescott filter The basic idea is to find a balance between the extent to which general growth trend follows the cyclical movement since long term growth rate is not likely to be perfectly constant and how smooth it is The HP filter identifies the longer term fluctuations as part of the growth trend while classifying the more jumpy fluctuations as part of the cyclical component


Observe the difference between this growth component and the jerkier data Economists refer to these cyclical movements about the trend as business cycles Figure 3 explicitly captures such deviations Note the horizontal axis at 0 A point on this line indicates at that year, there is no deviation from the trend All other points above and below the line imply deviations By using log real GNP the distance between any point and the 0 line roughly equals the percentage deviation from the long run growth trend Also note that the Y-axis uses very small values This indicates that the deviations in real GNP are very small comparatively, and might be attributable to measurement errors rather than real deviations


We call large positive deviations those above the 0 axis peaks We call relatively large negative deviations those below the 0 axis troughs A series of positive deviations leading to peaks are booms and a series of negative deviations leading to troughs are recessions

At a glance, the deviations just look like a string of waves bunched together—nothing about it appears consistent To explain causes of such fluctuations may appear rather difficult given these irregularities However, if we consider other macroeconomic variables, we will observe patterns in these irregularities For example, consider Figure 4 which depicts fluctuations in output and consumption spending, ie what people buy and use at any given period Observe how the peaks and troughs align at almost the same places and how the upturns and downturns coincide


We might predict that other similar data may exhibit similar qualities For example, a labor, hours worked b productivity, how effective firms use such capital or labor, c investment, amount of capital saved to help future endeavors, and d capital stock, value of machines, buildings and other equipment that help firms produce their goods While Figure 5 shows a similar story for investment, the relationship with capital in Figure 6 departs from the story We need a way to pin down a better story; one way is to look at some statistics


Stylized factsedit

By eyeballing the data, we can infer several regularities, sometimes called stylized facts One is persistence For example, if we take any point in the series above the trend the x-axis in figure 3, the probability the next period is still above the trend is very high However, this persistence wears out over time That is, economic activity in the short run is quite predictable but due to the irregular long-term nature of fluctuations, forecasting in the long run is much more difficult if not impossible

Another regularity is cyclical variability Column A of Table 1 lists a measure of this with standard deviations The magnitude of fluctuations in output and hours worked are nearly equal Consumption and productivity are similarly much smoother than output while investment fluctuates much more than output The capital stock is the least volatile of the indicators


Yet another regularity is the co-movement between output and the other macroeconomic variables Figures 4 – 6 illustrated such relationship We can measure this in more detail using correlations as listed in column B of Table 1 Procyclical variables have positive correlations since it usually increases during booms and decreases during recessions Vice versa, a countercyclical variable associates with negative correlations Acyclical, correlations close to zero, implies no systematic relationship to the business cycle We find that productivity is slightly procyclical This implies workers and capital are more productive when the economy is experiencing a boom They are not quite as productive when the economy is experiencing a slowdown Similar explanations follow for consumption and investment, which are strongly procyclical Labor is also procyclical while capital stock appears acyclical

Observing these similarities yet seemingly non-deterministic fluctuations about trend, the question arises as to why any of this occurs Since people prefer economic booms over recessions, it follows that if all people in the economy make optimal decisions, these fluctuations are caused by something outside the decision-making process So the key question really is: what main factor influences and subsequently changes the decisions of all factors in an economy

Economists have come up with many ideas to answer the above question The one which currently dominates the academic literature on real business cycle theorycitation needed was introduced by Finn E Kydland and Edward C Prescott in their 1982 work Time to Build And Aggregate Fluctuations They envisioned this factor to be technological shocks—ie, random fluctuations in the productivity level that shifted the constant growth trend up or down Examples of such shocks include innovations, bad weather, imported oil price increase, stricter environmental and safety regulations, etc The general gist is that something occurs that directly changes the effectiveness of capital and/or labour This in turn affects the decisions of workers and firms, who in turn change what they buy and produce and thus eventually affect output RBC models predict time sequences of allocation for consumption, investment, etc given these shocks

But exactly how do these productivity shocks cause ups and downs in economic activity Let's consider a positive but temporary shock to productivity This momentarily increases the effectiveness of workers and capital, allowing a given level of capital and labor to produce more output

Individuals face two types of tradeoffs One is the consumption-investment decision Since productivity is higher, people have more output to consume An individual might choose to consume all of it today But if he values future consumption, all that extra output might not be worth consuming in its entirety today Instead, he may consume some but invest the rest in capital to enhance production in subsequent periods and thus increase future consumption This explains why investment spending is more volatile than consumption The life cycle hypothesis argues that households base their consumption decisions on expected lifetime income and so they prefer to "smooth" consumption over time They will thus save and invest in periods of high income and defer consumption of this to periods of low income

The other decision is the labor-leisure tradeoff Higher productivity encourages substitution of current work for future work since workers will earn more per hour today compared to tomorrow More labor and less leisure results in higher output today greater consumption and investment today On the other hand, there is an opposing effect: since workers are earning more, they may not want to work as much today and in future periods However, given the pro-cyclical nature of labor, it seems that the above substitution effect dominates this income effect

Overall, the basic RBC model predicts that given a temporary shock, output, consumption, investment and labor all rise above their long-term trends and hence formulate into a positive deviation Furthermore, since more investment means more capital is available for the future, a short-lived shock may have an impact in the future That is, above-trend behavior may persist for some time even after the shock disappears This capital accumulation is often referred to as an internal "propagation mechanism", since it may increase the persistence of shocks to output

A string of such productivity shocks will likely result in a boom Similarly, recessions follow a string of bad shocks to the economy If there were no shocks, the economy would just continue following the growth trend with no business cycles

To quantitatively match the stylized facts in Table 1, Kydland and Prescott introduced calibration techniques Using this methodology, the model closely mimics many business cycle properties Yet current RBC models have not fully explained all behavior and neoclassical economists are still searching for better variations

The main assumption in RBC theory is that individuals and firms respond optimally all the time It follows that business cycles exhibited in an economy are chosen in preference to no business cycles at all This is not to say that people like to be in a recession Slumps are preceded by an undesirable productivity shock which constrains the situation But given these new constraints, people will still achieve the best outcomes possible and markets will react efficiently So when there is a slump, people are choosing to be in that slump because given the situation, it is the best solution This suggests laissez-faire non-intervention is the best policy of government towards the economy but given the abstract nature of the model, this has been debated

A precursor to RBC theory was developed by monetary economists Milton Friedman and Robert Lucas in the early 1970s They envisioned the factor that influenced people's decisions to be misperception of wages—that booms and recessions occurred when workers perceived wages higher or lower than they really were This meant they worked and consumed more or less than otherwise In a world of perfect information, there would be no booms or recessions


Unlike estimation, which is usually used for the construction of economic models, calibration only returns to the drawing board to change the model in the face of overwhelming evidence against the model being correct; this inverts the burden of proof away from the builder of the model In fact, simply stated, it is the process of changing the model to fit the data Since RBC models explain data ex post, it is very difficult to falsify any one model that could be hypothesised to explain the data RBC models are highly sample specific, leading somewho to believe that they have little or no predictive power

Structural variablesedit

Crucial to RBC models, "plausible values" for structural variables such as the discount rate, and the rate of capital depreciation are used in the creation of simulated variable paths These tend to be estimated from econometric studies, with 95% confidence intervalscitation needed If the full range of possible values for these variables is used, correlation coefficients between actual and simulated paths of economic variables can shift wildly, leading some to question how successful a model which only achieves a coefficient of 80% really iscitation needed


The real business cycle theory relies on three assumptions which according to economists such as Greg Mankiw and Larry Summers are unrealistic:1

1 The model is driven by large and sudden changes in available production technology

Summers noted that Prescott is unable to suggest any specific technological shock for an actual downturn apart from the oil price shock in the 1970s2 Furthermore there is no microeconomic evidence for the large real shocks that need to drive these models Real business cycle models as a rule are not subjected to tests against competing alternatives3 which are easy to supportSummers 1986

2 Unemployment reflects changes in the amount people want to work

Paul Krugman noted that this assumption would mean that 25% unemployment at the height of the Great Depression 1933 would be the result of a mass decision to take a long vacation4

3 Monetary policy is irrelevant for economic fluctuations

Nowadays it is widely agreed that wages and prices do not adjust as quickly as needed to restore equilibrium Therefore most economists, even among the new classicals, do not accept the policy-ineffectiveness proposition4

Another major criticism is that real business cycle models can not account for the dynamics displayed by US gross national product5 As Larry Summers said: "My view is that real business cycle models of the type urged on us by Ed Prescott have nothing to do with the business cycle phenomena observed in the United States or other capitalist economies" —Summers 1986

See alsoedit

  • Austrian business cycle theory
  • Business cycle
  • Dynamic stochastic general equilibrium
  • Lucas critique
  • Monetary-disequilibrium theory
  • New classical economics
  • New Keynesian economics
  • Say's law
  • Welfare cost of business cycles


  1. ^ Cencini, Alvaro 2005 Macroeconomic Foundations of Macroeconomics Routledge p 40 ISBN 0-415-31265-5 
  2. ^ Summers, Lawrence H Fall 1986 "Some Skeptical Observations on Real Business Cycle Theory" PDF Federal Reserve Bank of Minneapolis Quarterly Review 10 4: 23–27 
  3. ^ George W Stadler, Real Business Cycles, Journal of Economics Literatute, Vol XXXII, December 1994, pp 1750–1783, see p 1772
  4. ^ a b Kevin Hoover 2008 "New Classical Macroeconomics", econliborg
  5. ^ George W Stadler, Real Business Cycles, Journal of Economics Literatute, Vol XXXII, December 1994, pp 1750–1783, see p 1769

Further readingedit

  • Cooley, Thomas F 1995 Frontiers of Business Cycle Research Princeton: Princeton University Press ISBN 0-691-04323-X 
  • Gomes, Joao; Greenwood, Jeremy; Rebelo, Sergio 2001 "Equilibrium Unemployment" Journal of Monetary Economics 48 1: 109–152 doi:101016/S0304-39320100071-X 
  • Hansen, Gary D 1985 "Indivisible labor and the business cycle" Journal of Monetary Economics 16 3: 309–327 doi:101016/0304-39328590039-X 
  • Heijdra, Ben J 2009 "Real Business Cycles" Foundations of Modern Macroeconomics 2nd ed Oxford: Oxford University Press pp 495–552 ISBN 978-0-19-921069-5 
  • Kydland, Finn E; Prescott, Edward C 1982 "Time to Build and Aggregate Fluctuations" Econometrica 50 6: 1345–1370 doi:102307/1913386 JSTOR 1913386 
  • Long, John B, Jr; Plosser, Charles 1983 "Real Business Cycles" Journal of Political Economy 91 1: 39–69 doi:101086/261128 
  • Lucas, Robert E, Jr 1977 "Understanding Business Cycles" Carnegie-Rochester Conference Series on Public Policy 5: 7–29 doi:101016/0167-22317790002-1 
  • Plosser, Charles I 1989 "Understanding real business cycles" Journal of Economic Perspectives 3: 51–77 doi:101257/jep3351 JSTOR 1942760 
  • Romer, David 2011 "Real-Business-Cycle Theory" Advanced Macroeconomics Fourth ed New York: McGraw-Hill pp 189–237 ISBN 978-0-07-351137-5 

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