Statistical data, which are ordered in tabular form, can contain different types of numbers, which are to be explained using the categorization by Schröder (1985). These categories are: Frequency number, measure and ratio.

**Frequency number**describes the frequency that a certain event is happening, the incidence of a certain occurrence, such as the number of traffic fatalities per year.**Measures**in conjunction with a unit specify a dimension such as 28°Celsius or 10,5kg or 1000m.**Ratio**numbers specify a relation, also called relative values. An example is population density, which is defined as the ratio between the population number and the area. Ratio numbers can be divided into four further types of numbers, depending on the values that are related to it. These are:- Proportion numbers
- Measurement numbers
- Index numbers
- Relation numbers

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