Data that can be classified into two or more categories.
Note: When there is an order to the categories, the term used is ordinal data (e.g. stages of cancer or level of education). When there is no order, the term used is nominal data (e.g. blood group, civil status or ethnic origin). There is no mathematical relationship between the values (e.g. a person with Stage IV cancer is not twice as sick as a person with Stage II cancer).