The reverberation time is a key feature for describing the acoustic properties of a reverberant room. It can be computed from a measured Room Impulse Response but in many applications it has to be estimated blindly. Existing blind methods give accurate estimates but they often exhibit high variance across different speakers. In this paper, a low variance blind estimator of the reverberation time is derived from the decay rate distribution of the signal. The influence of the reverberation time on the statistical moments of the distribution is analyzed and one relevant moment is taken as an estimator. The variance of the estimator is reduced thanks to a prewhitening filter and a modification of the decay rate distribution. Experimental results confirm the accuracy of the method when the observed signal is sufficiently long.