The Real Business Cycle (RBC) Model receives a lot of criticism from online bloggers and from other economists. A lot of the criticism is justified. The model assumes away all frictions and market failures. It assumes that the consumers and workers can be analyzed as though they were all essentially the same or perhaps as though we could pay attention to only an average individual’s preferences. The most contentious aspect of the RBC model however has always been the assumed source of business cycle fluctuations. In the RBC model, variations in productivity, perhaps brought on by the inevitable unevenness in the pace of innovation, drive all of the variations in hours worked, investment, production and so forth.

I mentioned in a previous post that this stark version of the RBC model is not really taken very seriously by researchers anymore — at least with regard to the role of productivity shocks. Better measurement has deprived the canonical RBC model of the innovations necessary to generate cyclical variations in economic activity. While early RBC models used Solow residuals as proxies for actual changes in productivity, subsequent research demonstrated that these measures were virtually entirely due to variations in unobserved utilization (capital utilization, labor effort, etc.). Thus, in the data, variations in TFP occur at seasonal frequencies (which is pretty difficult to believe in the economy we live in today) and even in response to tax stimulus (an investment tax credit will stimulate investment and also “cause” measured TFP to rise). Even worse, the measured increases in the seasonal variations or in response to tax changes are essentially of the same magnitude as the variations observed over the business cycle. Papers that do attempt to adjust for unobserved input variations (say by including measured energy use) typically find that they eliminate a huge amount of variation in productivity. The well-known study by Basu, Fernald and Kimball (2006) produces “cleansed” Solow residuals which are at best unrelated to cyclical variations in GDP (Basu et al. actually claim that true productivity variations are negatively correlated with detrended GDP). Of course there are actual productivity shocks (e.g., Hurricane Katrina, the terrible 2011 Japanese Tsunami, the 2 day blackout in the northeast US in 2003, …) but none of these seem to be responsible for substantial changes in employment or production.

This begs the question: If the RBC model does not survive as a model of actual business cycle fluctuations, why do we still teach it in graduate macroeconomics?

I can think of three answers to this question. The first answer is due to its prominent historical place in the development of the field. Macroeconomics changed forever after the first-generation RBC models were developed. These models ushered in new methods and techniques many of which are still in use today. Similarly, the fact that we know that real shocks do not cause business cycle fluctuations (at least the way they were conceived by the original RBC theorists) is an important component of our understanding. Even when you are on a long voyage, it often is important to look back every now and then.

Second, the RBC model is an excellent pedagogical device. The RBC model is almost always the first DSGE model students confront and it is also functioning as the standard backdrop in more advanced DSGE frameworks. Many of the intuitions carry over and present themselves in more modern instances of the model. For instance, researchers have extended the basic framework to analyze tax policy, international business cycles, government spending shocks, and of course monetary policy. Often the correct intuition required for the more elaborate models can be seen in the original RBC framework.

Last, there may yet be situations in which the RBC model might be applicable. While modern advanced economies do not have business cycles that are driven by real shocks, other economies might. For example, suppose you wanted to analyze the economy of ancient Egypt. The Egyptian economy would be closely tied to the flooding of the Nile river and other types of weather shocks. If the waters don’t rise enough, food production will fall. If there is a particularly good year for growing, the Egyptians will accumulate a large stock of foods which might well be traded or stored. I would suspect that the effects of these real shocks might well have tremendous impacts on production, consumption, work, storage and so on and the RBC model might provide an interesting guide as to what patterns one might expect in the data. (If there is an enterprising student out there who has an idea of where we could find some actual data on production, etc. for ancient Egypt, send me an e-mail, I would love to write this paper with you … )