whether it takes the form of insurance, market pools, or costs averaged over lines of business, risk sharing ordinary reduces the variation of returns to the individual member. a reduction in variation (risk) of returns, given the same average overtime, is preferred if members are risk averse. the appropriate amount of risk in sharing depends on the extend of risk aversion of members and benefits of maintaining services at cost. in general, if variations in cost or return result from the action of an individual members, averaging costs or returns across members reward behavior that leaves the group worse off. if the variation is not controllable by the individual member, averaging may increase the utility of the group through the reduction of uncertainty.