Interpreting the Electorate Statistics
From: Judy Reinken
1. Here is the official technical stuff on NZDep96.
NZDep96 is an index which orders all the meshblocks in New Zealand on a scale of material and social deprivation. When necessary meshblocks were combined together to create small areas with usually resident population of at least 100 persons. Nine variables structured from responses to the 1996 Census of Population and Dwellings were entered into a simple principal components analysis [cf. Kendall, M. A Course in Multivariate Analysis. London: Charles Griffin & Co. Ltd, 1968]. The first principal component is a vector of coefficients of the 9 variables such that the residual variability among the meshblock groups is minimised. The nine variables, in order of their loading on the first principal component, are:
The choice of variables has been refined over the 20 years of development of similar indices. Variables were selected for inclusion in NZDep96 because they (1) were available from the Census and (2) reflected a dimension of material or social deprivation.
The index measures relative deprivation, with meshblocks ranked on the score of the first component and then grouped into deciles. In these maps the least deprived 10 % of meshblocks are dark blue and the most deprived 10% are dark red. The paler shades include the next least deprived or the next most deprived areas. The 60% of the areas near the average for New Zealand are left unshaded.
References:
Crampton P, Salmond C, Sutton F 1997. NZDep91: a new index of deprivation. Social Policy Journal of New Zealand, 9, 186-193.
Salmond C, Crampton P, Sutton F 1998. Research Report No 8, NZDep96 Index of Deprivation. Wellington, Health Services Research Centre.
2. Here is a discussion of the choice of percentages.
Percentage with no work includes any person aged 20-59 who reported neither full-time nor part-time work in the 1996 Census. The national average of 21% includes people who care for children but did not record that as either part- or full-time unpaid work. If child-rearing takes someone out of the workforce for 10 years each, then 12.5% of the 21% could be accounted for. The other 8.5% would reflect the jobless. Probably less than ten years is the average time spent in unpaid full-time child care.
Personal income below $15,000 before tax includes the minimum wage (take-home of $250 per week) and below. The poverty line has been estimated, in 1996, to be nearer $18,000, so minimum wage and below is really low. And, yes, the national proportion of 20- 59 people reporting income below this level is 37%. Differentials in this proportion range from 57% to 70% in places in the Far North District to 29%-31% in Wellington, Manukau eastern, North Shore and Lower Hutt.
Household incomes (adjusted for size) of below $30,000 include people eligible for Community Service Cards. And, yes, the national proportion of households with income below this level is 44%. Differentials in this proportion range from 74% - 62% in places in the Far North District to 25%-35% in Wellington, Manukau eastern, North Shore and Porirua!
3. Reading the Maps
The deprivation index bundles together indicators of poverty such as many people in an area not having a phone, not having a car, being unemployed or on a means-tested benefit, and being in a low-income household. Added to this are high levels of single- parent families in the area, having many people without educational qualifications, having many households which are renting rather than owning and having more persons per bedroom than usual.
Meshblocks in built up areas are often a city block, but in rural areas they may be large in area. The meshblocks are chosen to include about 100 people on average. In fact, in some places the meshblocks are empty, or nearly so. The calculation of the deprivation index has grouped mechblocks together in those cases so each area analysed has at least 100 residents. Roads and streets are often meshblock boundaries.
An area is shaded black when the deprivation score for all its people is in the most deprived 10% of areas in New Zealand. Such an area might include a few people who are well-off, but most of the people will be far below the poverty line.
Combining the areas shaded black with those dark stippled areas provides the location of the poorest fifth of New Zealand, often the level chosen for a poverty measure.
Areas that are empty of people or are in the average range are shaded grey. The white areas are ones where the richest 10% of new Zealanders are found. Again it is the average of the meshblock, so some less well-off people may be resident in that area.