 Since the late 1960s, alternative measures of risk have been developed. Perhaps the most influential of these was provided by Michael Rothschild and Joseph Stiglitz (1970): If we move probability mass from the centre to the tails of a probability distribution, while keeping its mean unchanged, then we increase the risk associated with the distribution. A measure based on this principle (mean preserving spread) can be constructed that has more attractive mathematical properties than those of the older standard deviation measure.