Saturna Capital has an interesting take on the calculation of the Graham / Shiller PE10, otherwise known as the Cyclically Adjusted Price Earnings ratio (CAPE). Saturna argues that The Market May Be Cheaper Than It Looks because the Consumer Price Index (CPI) provided by the Bureau of Labor Statistics (BLS) understates the true rate of inflation, a key input to the CAPE calculation:
Potentially Understated Inflation
Given that inflation estimates play an influential role in the calculation of the P/E10, it is important to investigate the assumptions behind the calculation of inflation. Traditionally, inflation is measured using the Consumer Price Index (CPI) provided by the Bureau of Labor Statistics (BLS). The CPI estimates inflation by measuring fluctuations in the average price of a basket of consumer goods and services that is deemed to be typical of the average urban consumer. However, due to a variety of reasons, largely political, the methodology used to calculate CPI has undergone many changes in the past 10 to 20 years. One of the most controversial changes was to alter the composition of the basket to reflect changes in consumer behavior over time.
In doing so, the BLS hoped to remove biases that cause the CPI to overstate the true inflation rate. Former chairman of the Federal Reserve Alan Greenspan advocated this alternative methodology, arguing that if the price of steak went up, consumers would choose to eat more hamburger meat instead.² He therefore concluded that unless hamburger meat replaced steak in the basket, inflation would be overstated because consumers were not actually spending more money. Skeptics view these changes as government manipulation, the purpose of which is to understate the true inflation rate, as well as the wage and other rate increases indexed to it (think Social Security).
Saturna uses an alternative measure of inflation: the Shadow Government Statistics’ (SGS) Alternate CPI:
Over time this recalibration of the CPI has produced lower inflation estimates than the “old school” method. In fact, the discrepancy has become rather large… Unlike Mr. Greenspan, however, we prefer steak to hamburger meat. Accordingly, we tend to believe the truth lies somewhere in between the BLS’s CPI and the Shadow Government Statistics’ (SGS) Alternate CPI.
The implications for CAPE using Shadow Government CPI are as follows:
The wide gap between the government-sanctioned CPI and the Shadow Government CPI presents a competing set of assumptions about how to measure the effect of rising prices on the average consumer and the market as a whole. The relevance to investment analysts is that higher inflation figures can have a dramatic impact on the current P/E10 ratio. For example, if inflation is assumed to be 5% annually, $1 in nominal earnings from 10 years ago would be worth approximately $1.63 in today’s dollars. At 10% annually, $1 in nominal earnings from 10 years ago would be worth about $2.59 today. Using a higher inflation estimate therefore increases average real earnings over the 10-year period, and thus lowers the P/E10 ratio. If we assume the SGS figures are correct, then the current P/E10 based on the average closing price during the month of June is about 14x (see chart below). This ratio is much lower than the current P/E10 of near 20x using traditional CPI figures.
Hat tip Ben Bortner.