Final answer:
Classifying head injuries by severity is an example of ordinal data, where categories are ranked in a specific order without precise quantifiable differences.
Step-by-step explanation:
Classifying head injuries according to level of severity is an example of ordinal data. Ordinal data is used to categorize the data in a specific order without determining the exact differences between them. It is more specific than nominal data, which only categorizes data without any order, and less specific than interval or ratio data, which involve exact measurements and the latter includes a true zero point.
For instance, head injuries might be classified as mild, moderate, or severe. This classification clearly has an order (mild is less severe than moderate, and moderate is less severe than severe), but the exact difference between these categories is not quantified. Therefore, it fits perfectly within the definition of ordinal scale level data.