Types of Data

Think about any collected data that you have experience of; for example, weight, sex, ethnicity, job grade, and consider their different attributes. These variables can be described as categorical or quantitative.

The table summarises data types and their associated measurement level, plus some examples. It is important to appreciate that appropriate methods for summary and display depend on the type of data being used. This is also true for ensuring the appropriate statistical test is employed.

Type of data Level of measurement Examples
Categorical Nominal
(no inherent order in categories)
Eye colour, ethnicity, diagnosis
(categories have inherent order)
Job grade, age groups
(2 categories – special case of above)

Quantitative (Interval/Ratio)

(NB units of measurement used)

(usually whole numbers)

Size of household (ratio)
(can, in theory, take any value in a range, although necessarily recorded to a predetermined degree of precision)

Temperature °C/°F (no absolute zero) (interval)

Height, age (ratio)