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The utility function u(c) is defined only up to positive affine transformation – in other words, a constant could be added to the value of u(c) for all c, and/or u(c) could be multiplied by a positive constant factor, without affecting the conclusions. An agent is risk-averse if and only if the utility function is concave.
Below is an example of a convex utility function, with wealth, ' ' along the x-axis and utility, ' ' along the y-axis. The below graph shows how greater payoffs result in larger utility values at an increasing rate. Showing that the person with this utility function is "risk-loving".
This variably curving utility function would thereby explain why an individual is risk-loving when he has more wealth (e.g., by playing the lottery) and risk-averse when he is poorer (e.g., by buying insurance). The function has been used widely, including in the field of economic history to explain why social gambling did not necessarily mean ...
To explain risk aversion within this framework, Bernoulli proposed that subjective value, or utility, is a concave function of money. In such a function, the difference between the utilities of $200 and $100, for example, is greater than the utility difference between $1,200 and $1,100.
The power utility function occurs if < and =. The more special case of the isoelastic utility function, with constant relative risk aversion, occurs if, further, b = 0. The logarithmic utility function occurs for = as goes to 0.
Risk aversion (red) contrasted to risk neutrality (yellow) and risk loving (orange) in different settings. Left graph: A risk averse utility function is concave (from below), while a risk loving utility function is convex. Middle graph: In standard deviation-expected value space, risk averse indifference curves are upward sloped.
The value function that passes through the reference point is s-shaped and asymmetrical. The value function is steeper for losses than gains indicating that losses outweigh gains. Prospect theory stems from loss aversion, where the observation is that agents asymmetrically feel losses greater than that of an equivalent gain. It centralises ...
The utility function whose expected value is maximized is concave for a risk averse agent, convex for a risk lover, and linear for a risk neutral agent. Thus in the risk neutral case, expected utility of wealth is simply equal to the expectation of a linear function of wealth, and maximizing it is equivalent to maximizing expected wealth itself.