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3228.0.55.001 - Population Estimates: Concepts, Sources and Methods, 2009  
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Contents >> Estimating births and deaths >> Revised estimates of births and deaths

REVISED ESTIMATES OF BIRTHS AND DEATHS

5.12 Revised estimates of quarterly birth and death occurrences are calculated by applying an inflation factor to birth and death occurrence data. They are published in Australian Demographic Statistics (cat. no. 3101.0) released 21 months after the end of each financial year.


Registration lags

5.13 There are two types of registration delays, or lags for births and deaths in a given period. The historical lag is the delay between births or deaths registered in the relevant period and their date of occurrence (i.e. looks into the past). Conversely, a future lag is the delay between births or deaths occurring in the target period and their (eventual) date of registration (i.e. it looks into the future).

5.14 The main principle behind the method used for revising birth and death occurrence estimates is that the historical and future registration lags for a quarter are similar, although this can change if registration procedures change. In other words, the historical lag derived from registration data can be used to indicate the future lag for occurrence data.


Estimating occurrences not yet registered

5.15 To determine the revised estimate for a particular period, the occurrence data that will be subject to inflation needs to be determined. To enable publication by 21 months after the financial year involved, registration data for the 15 months after the end of the financial year are available. For example, to publish revised data in March 2009, only registrations up to and including the September quarter 2008 were available for births and deaths which occurred in the 2006-07 financial year. This corresponds to 9 quarters (September quarter 2006 to September quarter 2008) in which births and deaths occurring in the 2006-07 financial year could have been registered. Thus, when inflating September quarter 2006 data, occurrence data with a future registration lag of less than or equal to 9 quarters are available.

5.16 Occurrence data for a particular quarter in the year (i.e. September, December, March or June) are adjusted based on registration data for the same corresponding quarter in the most recent year. This is so the most recent registration lag patterns available can be used. In the case of September quarter 2006 occurrences, a historical lag of 9 quarters is applied to registrations in the September quarter 2007 to obtain an inflation factor.

5.17 The proportion, p, of all registrations for the quarter that occurred within the historical lag period is determined by:

Equation: eq5_1

5.18 The inflation factor, f, for the quarter can be calculated such that:

Equation: eq5_2

5.19 For example, the inflation factor for births occurring in September quarter 2006 (termed fS06) would be:

Equation: eq5_3

where:

      BRegS07 = the total number of births registered in the September quarter 2007; and
      BRegS07,-9q = the number of births registered in the September quarter 2007 with an historical lag <= 9 quarters (i.e. occurring between the September quarter 2005 and September quarter 2007)

5.20 The estimate is calculated by applying the inflation factor to the count of births/deaths by state/territory on file. The birth estimate is expressed as:

B = f BOccReg

where:
      B = the estimate of births
      BOccReg = the births occurring in the quarter and registered within the future lag period

5.21 For example, the estimate of births occurring in September quarter 2006 is:

BS06 = f BOccS06RegS08,-9q

where:
      BS06 = the estimate of births occurring in September quarter 2006
      BOccS06RegS07,-9q = the number of births which occurred in September quarter 2006 registered in the period September quarter 2006 to September quarter 2008

5.22 This method is detailed further in Demography Working Paper: 1998/2 - Quarterly Birth and Death Estimates (cat. no. 3114.0), although the previous historical lag period of 7 quarters is discussed (in March 2009, the publication of the revised financial year data changed from 15 months after the end of the financial year to 21 months).





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