If date of birth is not known or cannot be obtained, provision should be made to collect or estimate age. Collected or estimated age would usually be in years for adults, and to the nearest three months (or less) for children aged less than two years. Additionally, an estimated date flag or a date accuracy indicator should be reported in conjunction with all estimated dates of birth.

For data collections concerned with children's services, it is suggested that the estimated date of birth of children aged under 2 years should be reported to the nearest 3 month period, i.e. 0101, 0104, 0107, 0110 of the estimated year of birth. For example, a child who is thought to be aged 18 months in October of one year would have his/her estimated date of birth reported as 0104 of the previous year. Again, an estimated date flag or date accuracy indicator should be reported in conjunction with all estimated dates of birth.

Information on date of birth can be collected using the one question:

What is your/(the person's) date of birth?

In self-reported data collections, it is recommended that the following response format is used:

Date of birth: _ _ / _ _ / _ _ _ _

This enables easy conversion to the preferred representational layout (DDMMYYYY).

For record identification and/or the derivation of other metadata items that require accurate date of birth information, estimated dates of birth should be identified by a date accuracy indicator to prevent inappropriate use of date of birth data. The linking of client records from diverse sources, the sharing of patient data, and data analysis for research and planning all rely heavily on the accuracy and integrity of the collected data. In order to maintain data integrity and the greatest possible accuracy an indication of the accuracy of the date collected is critical. The collection of an indicator of the accuracy of the date may be essential in confirming or refuting the positive identification of a person. For this reason it is strongly recommended that the data element Date—accuracy indicator, code AAA also be recorded at the time of record creation to flag the accuracy of the data.

Privacy issues need to be taken into account in asking persons their date of birth.

Wherever possible and wherever appropriate, date of birth should be used rather than age because the actual date of birth allows a more precise calculation of age.

When date of birth is an estimated or default value, national health and community services collections typically use 0101 or 0107 or 3006 as the estimate or default for DDMM.

It is suggested that different rules for reporting data may apply when estimating the date of birth of children aged under 2 years because of the rapid growth and development of children within this age group which means that a child's development can vary considerably over the course of a year. Thus, more specific reporting of estimated age is suggested.

National Health Data Committee

National Community Services Data Committee

Standards Australia 2002. AS5017—2002 Health Care Client Identification. Sydney: Standards Australia

Standards Australia 2004. AS4846—2004 Health Care Provider Identification. Sydney: Standards Australia