In the post-WWII period, U.S. stock returns have averaged 9%, whereas returns on treasury bills have been around 1%. Standard theories attribute such systematic differences in expected returns among different assets to risk. According to the Consumption-based Capital Asset Pricing Model (CCAPM) of Lucas (1978) and Breeden (1979), investors are willing to accept low returns in exchange for insurance against consumption risk. However, the risk of the stock market as measured by the covariance of stock returns with aggregate consumption growth is insufficient to justify the large risk premium observed in historical stock return data (Mehra and Prescott (1985)).
In an effort to reconcile the observed high equity premium and low consumption risk within the CCAPM framework, extant literature has explored modifications in investor preferences (Sundaresan (1989), Constantinides (1990), Epstein and Zin (1991), Campbell and Cochrane (1999), Bansal and Yaron (2004), Hansen, Heaton, and Li (2008), and Malloy, Moskowitz, and Vissing-Jorgensen (2009)), implications of incomplete markets (Constantinides and Duffie (1996)), market imperfections (Mankiw and Zeldes (1991), Constantinides, Donaldson, and Mehra (2002)) and alternative ways of measuring aggregate consumption risk (Ait-Sahalia, Parker, and Yogo (2004), Parker and Julliard (2005), Jagannathan and Wang (2007), and Jagannathan, Takehara, and Wang (2007)). Recently, Savov (2010) proposed an alternative approach using annual garbage generation as a measure of consumption, which is twice as volatile as the standard NIPA consumption measure (real per capita personal expenditure on nondurable goods and services) and highly correlated with market returns. As a result, this measure yields a more modest implied relative risk aversion coefficient than those obtained using conventional NIPA consumption expenditures.