Logarithmic utility functions represent a constant relative risk aversion of one by definition in economics and expected utility theory, requiring no empirical citation.
The claim states a fundamental, definitional mathematical property of logarithmic utility functions within expected utility theory (specifically, that the coefficient of relative risk aversion is -c * u''(c) / u'(c) = 1 for u(c) = ln(c)). This is a textbook mathematical identity rather than an empirical proposition requiring validation from specific studies.