Variables must have 2 qualities s: attributes must be exhaustive, attributes must be mutually exclusive. Variables whose attributes have only characteristics of exhaustiveness (jointly exhaustive) and mutual exclusiveness i. e a variable with just discrete categories cannot be ranked. E. g gender, religious affiliation , political party affiliation, birthplace, college, hair colour. Allcan say about 1 people is that they are either the same of different. German shepherd is different than an australian cattle dog. Cannot say one is more or less dog breedy than the other. Jointly exhaustive: every possible observation can be classified into a attribute of the variable. Categories shoule be sufficient so that all observations can fit into one of them. Mutually exclusive: every observation must be classified into one and only one attribute. Observation shout not be able to fit into two or more attributes. Variables with attributes that can be logically rank ordered; different attributes represent relatively more or less of the variable.