Most economists know that the CPI is overestimated and therefore prefer the PCE price index. However, monthly CPI data is consistently released before PCE data for a given month. One would think that they move in the same direction and be highly correlated. Indeed, in the past five years, the correlation is 0.96. Therefore, it stands to reason that the there is less new relevant information on the PCE release dates than on the CPI release dates. Yes, CPI is biased, but it still contains some information about prices and it is known well prior to the more accurate PCE numbers.
Supply and Demand react to new information. Sometimes the new information changes our expectations about the future, and other times we learn that our beliefs about goods and assets were previously not quite right. So, with new relevant information comes new prices as people update their beliefs and expectations.
Let’s get financial.
Way back in the late 1970s and early 80s, Kydland and Prescott proposed rational expectations theory. This line of research arose, in part, because the Phillips curve ceased to describe reality well. Amid increasing inflation, people began to anticipate higher prices to a relatively correct degree when making labor, supply chain, and pricing decisions. Kydland and Prescott argued that individuals understand the rules of the game or how the world works – at least on average.
An increase in the money supply would increase total national spending, and increase demand for goods. However, firms also experienced increasing revenues and demanded more inputs such as commodities, capital, and intermediate goods. Because there were no greater productivity earlier in the supply chain, price roses. Firms began to understand that greater demand would eventually find its way to causing greater costs. Therefore, firms began raising prices before the cost of resources rose, increasing their willingness to pay for inputs and, ironically, hastening the increase in input prices. As a result, increases in the money supply began having substantial short-run price effects and negligible output effects.
However, assuming that people understand the rules of our economic system and ‘how the world works’ is hard to swallow. It is not at all clear that the typical economist understands monetary theory, much less clear that the typical person has a good understanding. Fortunately, another theory of expectations can help carry some of the load and achieve similar results.