Data are unprocessed collection of raw facts gathered from various sources explicitly or implicitly. Data can be divided into two different types: categorical and numerical. Categorical data can be sorted into the categories of values or observations and grouped as nominal or ordinal. The main difference between these two groups, in the ordinal data, the categories are in certain orders. Unlike numerical data, categorical data cannot be measured. Numerical data is
divided into two types: discrete and continuous. For discrete data, values are countable and can only take particular values. There is a clear separation
between different possible values. Continuous data are not restricted to defined distinct values.