A statistical system, at its most fundamental, counts things. Thus, in any statistical investigation, a first step is to decide what to count to most effectively measure the topic of interest. As people are central to issues of wellbeing, the most commonly used counting unit is the person. However, other counting units may be more appropriate in certain instances. For example, many individuals share resources with their family or household, and the family and household counting units are therefore often used in assessing economic wellbeing. Some commonly used counting units are defined below.
People can be classified into a wide range of categories, and then counted to reflect many different areas of interest. For example, they may be counted as males or females, as people of a certain age, as students, employees, job seekers, prisoners, patients, household members or victims of crime, to name a few.
For statistical purposes the ABS defines a family as two or more persons, one of whom is at least 15 years of age, who are related by blood, marriage (registered or de facto), adoption, step or fostering, and who are usually resident in the same household. The basis of a family is formed by identifying the presence of a couple relationship, lone parent-child relationship or other blood relationship. Some households will, therefore, contain more than one family.
Many resources are shared among people who live together, even if they are not related to one another. A household is defined by the ABS as a group of two or more related or unrelated people who usually reside in the same dwelling, who regard themselves as a household and who make common provision for food or other essentials for living; or a person living in a dwelling who makes provision for his or her own food and other essentials for living, without combining with any other person.
An income unit is one person or a group of related persons within a household, whose command over income is assumed to be shared (e.g. a married couple). Membership is based, in part, on the concept of dependency. An income unit is formed for each couple and their dependent children, and for each lone parent and dependent children. Dependent children are persons aged under 15 years, and those aged 15-24 years who are full-time students, live with a parent, guardian or other relative, and do not have a spouse or children of their own living with them. Non-dependent children are regarded as being separate income units.
Other counting units include events (e.g. births, deaths, marriages, visits to museums), transactions (e.g. expenditure), resources (e.g. cash income, household assets such as vehicles, public facilities such as schools or hospitals), or even units of time (e.g. time spent on certain activities, hours worked).