Whether the underlying distribution is log-normal or not, the size of the difference between these averages (or their logarithms) gives a measure of the width of that distribution. The idea and intent are reminiscent of the weight-average and number-average molecular weights that are widely used in polymer chemistry as simple measures that characterize polymer polydispersity. In practice, calculating rate-average relaxation rates and time-average relaxation rates is conveniently achieved using amplitudes and rates from either the SBP analysis or from ARM+LSQ.