The Brain from Inside Out

by György Buzsáki

Perhaps the most common skewed distribution in biology is the logarithmic-normal or log-normal distribution.23 This distribution is right-skewed on a linear scale but looks bell-shaped when the logarithms of the observed values are plotted. In other words, a log-normal distribution is a probability distribution of a random variable whose logarithm is normally distributed. Examples from biology include the number of species per family, survival times of species, sizes of fruits, pharmacological effects, times to first symptoms of infectious diseases, and blood pressure distribution within an age group, just to list a few. Basic physiologic processes, such as resting heart rate, visual acuity, and metabolic rate, also show a skewed distribution. In economics, incomes are often well fitted to a log-normal function.24