Abstract
The Arrow-Pratt (A-P) definitions of absolute and relative risk aversion dominate the discussion of risk aversion and defining “more risk averse”. Ross (Econometrica 49:621–663, 1981) notes, however, that being A-P more risk averse is not sufficient for addressing many important comparative static questions. Consequently he introduces “a new and stronger measure for comparing two agents’ attitudes towards risk…”. Ross does not provide a corresponding measure of risk aversion. This paper uses a normalized measure of concavity to characterize the Ross definition of strongly more risk averse on bounded intervals. Other properties and uses of these normalized measures of concavity are also presented.
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Notes
Pratt (1990) points out several weaknesses of the Ross strongly more risk averse order.
The correct upper and lower bounds of outcome distributions are often specific to a particular decision problem. For many utility functions, utility is defined for every level of wealth, but the restriction to an interval is imposed to give Ross comparability over that interval. Thus, for the same utility function and different decision problems, the interval [a, b] can differ in location and size.
For a utility function such as the negative exponential function which displays A-P constant absolute risk aversion, any finite values for a and b are allowed. For constant relative risk aversion, however, the logarithmic and power functions require that a > 0 be satisfied.
Friedman and Savage (1948) use the second derivative of u(x) to define the utility premium.
Eeckhoudt and Schlesinger (2009) discuss the utility premium in the context of savings and other decisions and attribute the utility premium concept to Friedman and Savage (1948). The utility premium is also studied in detail in Stone (1970) and used in Menezes et al. (1980), Eeckhoudt and Schlesinger (2006), Menegatti (2007) and Crainich and Eeckhoudt (2008), among others.
In addition to being arbitrary to a scale factor, -u″(x) is a less desirable measure of risk aversion because of this unit issue as well.
Normalization factors exist that allow similar results in the competitive firm and insurance demand decision models.
Using the rate of substitution, instead of the risk premium, to quantify an individual’s reaction to risk increases turns out to be even more significant when the risk increases are of a higher degree, as shown in Liu and Meyer (2013a).
In their study of the relationship between changes in risk aversion and changes in prudence (− u‴(x)/u″(x)), Eeckhoudt and Schlesinger (1994) also work with these families of utility functions. They point out that, using the parameterization of the current paper, prudence remains the same but the A-P risk aversion increases as αu increases. Note also that these families of utility functions include the so-called “linex” family, where w(x) takes the form of any CARA utility function, as a special case (Denuit et al. 2013).
For a summary of the issues in this line of research, see Gollier (2001).
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Support from the Private Enterprise Research Center at Texas A&M University is gratefully acknowledged. We thank Louis Eeckhoudt and Stephen Ross for helpful comments and suggestions on an early draft. Two reviewers also provided helpful comments. An early version of this paper was presented at Risk and Choice: A Conference in Honor of Louis Eeckhoudt, Toulouse, France, July 13, 2012. We thank conference participants, especially Ed Schlee, for valuable comments.
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Liu, L., Meyer, J. Normalized measures of concavity and Ross’s strongly more risk averse order. J Risk Uncertain 47, 185–198 (2013). https://doi.org/10.1007/s11166-013-9173-9
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DOI: https://doi.org/10.1007/s11166-013-9173-9