# Census Income Statistics

Keywords: Distributional Economics; Maori; Statistics;

The following summarises the income statistics used in the Listener economics columns of the March 11 & 25, and April 7.

The data is derived directly from the official Population Census for the relevant years. As the column details, it is reported income including social security benefits, before tax and is on a personal, not household basis. It includes only ‘adults’ over 15.  The Census is held in Martch, and the convention is that incomes are reported to the year ending march.
The 1986 data is included here, although not referred to in the columns. A change in the way social security was paid in 1987 may mean that comparability is compromised. Please dont use the 1986 data without mentioning this.

The mean (average) and median (middle) incomes are adjusted by the Consumer Price index to 2005/6 prices and are comparable across time. The decile shares are calculated by linear interpolation.  (Deciles are tenths of the population ranked  from lowest to highest.) Note that the bottom decile includes those adults without income, including students and homemakers.

If you want to calculate the average reported income (in 2005/6 prices) of any decile take the decile share, multiply it by the annual mean, and divide by 10 (the size of the decile). Thus the average income for those in the top decile in 2005/6 was \$33,700*35.9/10 = \$121,000. The figure for those in the top decile in 2000/1 was \$30,900*37.3/10 = \$115,300 in 2006 prices..

To calculate the nominal income multiply by the CPI index. Thus the top decile in 2001 reported an income of \$115,300* .884 = \$101,900 (i.e in 2000/1 prices.)

INCOME AND DECILE DATA FROM POPULATION CENSUS

 Mean \$27,200 \$25,700 \$27,900 \$30,900 \$33,700 Median \$22,100 \$19,000 \$19,000 \$20,900 \$24,400 DECILE Bottom 0.0% 0.3% 0.2% 0.2% 0.2% 2 1.9% 2.5% 1.9% 1.8% 1.8% 3 5.4% 3.8% 3.4% 3.3% 3.4% 4 4.9% 5.0% 4.7% 4.5% 4.6% 5 7.3% 6.5% 6.0% 5.9% 6.3% 6 9.1% 8.4% 7.9% 7.8% 8.2% 7 11.2% 10.7% 10.3% 10.1% 10.3% 8 13.7% 13.6% 12.9% 12.7% 12.6% 9 17.2% 17.2% 16.8% 16.6% 16.7% Top 29.3% 31.9% 35.8% 37.2% 35.9% CPI 0.486 0.745 0.822 0.884 1.000

Table notes.

The year is the date reporting and refers to the year ending March (not December).
The 1986 year may not be comparable with later ones.
The mean and median incomes are in 2005/6 prices

(Note. It is necessary to estimate the average income in the upper open interval. This was doen by using the data form top two intervals to estimate a Pareto coefficient for the upper tail. They were all just under 2. Losses were treated as zero income.)

Maori Data

PROPORTION OF MAORI IN INCOME QUINTILES
 1986 1991 1996 2001 2006

 TOP 11.6% 10.2% 11.8% 11.4% 12.0%
 SECOND 20.6% 17.7% 18.9% 19.4% 20.0%
 THIRD 23.1% 22.2% 21.3% 22.0% 23.2%
 FOURTH 20.7% 26.1% 23.1% 22.4% 21.2%
<> <>BOTTOM  <>24.0% <>23.9% <>24.9% <>24.7% <>23.7%