Series breaks: A new definition of population was adopted for the 1981 Census. Population is defined as the number of people who usually reside in Australia, that is, 'Australian residents'. Prior to this population had been defined as the number of people actually present at a given time (at the census). This meant the number of people actually counted included foreign tourists but excluded Australians abroad. Population estimates based on this new concept were compiled back to 1971. Therefore, data on the distribution of the population by age and sex contains a series break between 1970 and 1971.