*Statistics* is the study of the collection, organization, analysis, interpretation and presentation of data. In this section we provide *descriptive statistics*, that is, functions of the input which each summarize an intuitive aspect of the given input. The most important descriptive statistics are those describing *central tendency*, such as mean, median, and mode, and those describing *dispersion*, such as variance, standard deviation, and range. Other statistics include those describing *dependency* between two or more data-sets, such as correlation, and mutual information. Under probabilistic assumptions, i.e. an underlying *population distribution*, the descriptive statistics can often be shown to be estimators, with varying properties, of the parameters of the population distribution.