**Inferential statistics** consists of methods that use sample results to make decisions or predictions about a population (Mann 2012, Weiss 2010). This area of applied statistics is fundamental in all situations, when knowledge about the population is limited or even missing at all, which is the case for most real life applications. In addition, in many cases it is just too expensive, very time consuming, or virtually impossible to collect data of every member of a population. Therefore, a sample is taken from the population and an appropriate sample statistic is calculated. Then, based on the value of the sample statistic, a value is assigned to the corresponding (unknown) population parameter.

This procedure, by which a numerical value is assigned to a population parameter based on the information collected from a sample is called **estimation**. The numerical value is called an **estimate** of the population parameter. The sample statistic used to estimate a population parameter is called an **estimator** (Mann 2012).