The population distribution is the probability distribution derived from the knowledge of all elements of a population (Mann 2012). We know that depending on the population of interest the random variable of interest may be a discrete variable, is to say a variable that, at least in principle is countable, or the random variable of interest may be a continuous variable, and thus a variable that can take any value within a given interval. Both, the discrete and the continuous probability distribution may be described by statistical parameters, such as the mean, the standard deviation the median, the mode, among others. These parameters describing the population are, however, always constant, because the population is the set of all elements and thus population statistics do not change. For example, for any population data set, there is only one value of the population mean, one value for the standard deviation and so on.

---