Understanding supplementary codes in Census variables

Most variables in the Census Dictionary have supplementary codes and categories. We use supplementary codes to code responses that do not fit into the main categories.

They include:

• Not stated
• Not applicable
• Overseas visitor
• Inadequately described
• So described
• Not further defined (nfd)
• Not elsewhere classified (nec)

Note – when calculating percentages in variables which have Inadequately described, So described, Not elsewhere classified, or Not further defined, we suggest including these in the totals. These are all categories obtained from valid responses to Census questions.

Not stated means the question wasn’t answered on the Census form.

Most Census variables have a Not stated category. The exceptions are:

• Age
• Sex
• Registered marital status
• Place of usual residence

We impute data for these variables when the question wasn’t answered. Imputation is a statistical process to predict values where we cannot derive a response.

The other exceptions are family and household relationship variables. If some people in the household didn’t state their relationship to each other, we work out household and family structure from other information provided. If it can’t be determined, we consider it an Other non-classifiable household.

When calculating percentages of a population you can include or exclude Not stated responses in the total population (denominator) but note that your approach may affect the interpretation of the data. In general, for Census products such as QuickStats, we include Not stated responses in the total population when calculating percentages.

When you exclude Not stated responses from the total population, you’re distributing them across the other categories. In doing so, you’re assuming the stated responses are representative of the Not stated responses.

This may not be a safe assumption to make – some population groups may be less likely to answer certain questions than others. For example, low-income earners may be less likely to answer the personal income question than high-income earners.

Not applicable means the question wasn’t applicable to the person so they did not need to respond.

For example, questions relating to employment are only applicable for people aged 15 years and over. People aged under 15 years are in the Not applicable category.

The Census dictionary covers who or what is included in the Not applicable category for each variable.

An Overseas visitor is someone who usually lives in another country and is in Australia for less than one year. These are people who have selected ‘Other country’ for the question ‘Where does the person usually live?’ 

We coded overseas visitors differently in censuses prior to 2001.  For historical data, you should check publications for the relevant year in Historical Census data to see if we included or excluded overseas visitors in the data.

For more information, see Visitors to Australia in the Census Dictionary.

This category captures responses that aren’t specific enough to be included in any level of a category.

For example, if a person gave a response to the occupation question that did not relate to any occupations listed in the Occupation classification, we code it to Inadequately described.

This category holds responses that are broader than the highest category.

For example, if a person listed their ancestry as ‘European’ we don’t have enough information to code it to North-West European, or Southern and Eastern European so we code it to European so described.

Not elsewhere classified (nec) categories are used for responses where there isn’t a specific category in the classification.

For example, if someone gave their ancestry as Greenlandic, we code it to Northern European nec as there isn’t a Greenlandic category. We need the residual category because the ancestries listed under the Northern European category are not all the known Northern European ancestries.

Not further defined (nfd) categories are used when enough information exists to partially code a response, but we do not have enough to code it to the most detailed category in the classification.

For example, if someone listed their birthplace as ‘Czechoslovakia’ we code it to Eastern Europe nfd because we don’t know if they were born in Czechia or Slovakia.

Another example is religion. If a person listed their religious belief as ‘Any religion’, we don’t have enough information to code it to a more detailed category, so we code it to Religious belief nfd.