How the decile is calculated

Information on the method the Ministry of Education uses to calculate school deciles.

A major reassessment of all school deciles is undertaken following each 5-yearly Census of Population and Dwellings.  In intervening years, schools can apply for a review of their decile on the basis of perceived change in the socio-economic status (SES) of students in a school’s catchment.

A school's decile indicates the extent to which the school draws its students from low socio-economic communities. Decile 1 schools are the 10% of schools with the highest proportion of students from low socio-economic communities, whereas decile 10 schools are the 10% of schools with the lowest proportion of these students. A school's decile does not indicate the overall socio-economic mix of the school.

Census information is used to calculate the decile. A school provides its student addresses and these are used to determine which areas its students come from.

The student addresses are assigned to the smallest Census areas, called meshblocks. A meshblock contains around 50 households. However, only Census information for households with school-aged children is used. The number and percentage of students from each meshblock is determined and the meshblock is examined against five socio-economic factors.

Note: It is not the general area around the school that is used to calculate the decile, but the specific meshblocks where students live.

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The five factors that make up the socio-economic indicator:

  1. Household income - the percentage of households with equivalent income (ie adjusted for the number of adults and children in the household and the age of the children) in the lowest 20% nationally. Households with a member who is employed are usually not included in this group nor are all households supported by a benefit (since more than 20% of families are dependent on a benefit).
  2. Occupation - the percentage of employed parents in occupations that are at skill levels 4 or 5 (of the 1 to 5 levels of the Australia and New Zealand Standard Classification of Occupations ANZSCO). These include all labourers, all machine operators and assemblers, and others who work in occupations at these lower skill levels irrespective of the sector/ type/ profession involved.  
  3. Household crowding – the percentage of households with an equivalised crowding index greater than one. This index is the proportion of household members per bedroom adjusted for the presence of children under 10 years of age, every two of whom are assigned to share a bedroom; couples, and others are each assigned their own bedroom.
  4. Educational qualifications - the percentage of parents with no tertiary or school qualifications.
  5. Income support - the percentage of parents who directly (ie not as a partner) received a Domestic Purposes Benefit, Unemployment Benefit or Sickness and Invalid's Benefit in the previous year. This does not include parents receiving Family Support.

Census information is used to calculate these factors for each meshblock. The ministry does not have access to the individual Census information, only the information for the meshblock as a whole which it accesses in confidence through Statistics New Zealand.

The five census factors are weighted by the number of students from each meshblock. This means that meshblocks where only a few of a school's students live will have little impact on its decile, while those having more will have a greater impact etc.

Schools are ranked in relation to every other school for each of the five factors and receive a score according to the percentile that they fall into. The five scores for each school are added together (without any weightings) to give a total. This total gives the overall standing of a school in relation to all other schools in the country, enabling the ministry to place schools into ten groups called deciles, each having the same number of schools.

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Reviews of deciles

Deciles may be reviewed annually on the basis of perceived change in the socio-economic status (SES) of students in a school’s catchment.  This may involve a change in the shape of the catchment (which may be associated with a SES change) and/or a change in SES without apparent catchment change.

The Ministry of Education advertises the review process in the Education Gazette around August of each year with application forms available by contacting the sponsor.  A school applying for a review must state whether their case is one of physical catchment change and/or SES change without physical catchment change.

When applying for a review under the physical catchment change criteria, a school must supply the addresses for all of its students.  The five factors for the school are then calculated using the Census method described earlier.

If a school is applying for a review under the change in SES, it must survey the households of the students to gain the information needed to calculate the five factors for the school.  This calculation is independent of the Census.

A school may apply on both grounds.  In this situation, it must supply both address information and survey results.

More information on the Review of Deciles is available here.

Where to find an individual school's decile

A list of schools with their deciles as well as their contact details is available as a downloadable spreadsheet on Directory of Educational Institutions.

Content last updated: 16 January 2009