Deciles matter for New Zealand schools in ways other than funding allocation.

As schools await for another decile review post 2013 census - we explore different data sets related to the decile system, including school rolls and subject entries for NCEA.

The difference between rich and poor schools in New Zealand

Earlier this year, we published an interactive on deciles in NCEA - which looked at the differences across deciles for the number of entries in each subject.

Graham Jenson, a software engineer in Wellington, published a separate interactive(above) on his blog at, which used the same data set but asked different questions.


To view the interactive on mobile click here.

We're republishing this interactive, which was posted under a blog post titled 'The Difference Between Rich and Poor Schools in New Zealand', for the first time on the Herald site. The full blog post is worth reading for more insight regarding limitations of such analysis.

For Jenson, the interactive is an attempt at answering these two questions:

- How effective is the decile strategy at equalling out education outcomes in New Zealand?

- What are the differences of education outcomes between the 10 deciles?

The code for the above interactive is available here.

Decile drift and limitations of the data set

Today, we published an interactive 'the decile drift' showing how school rolls have changed for different ethnicities in different deciles since 1996.

This interactive uses the school rolls data, which is broken down for each decile and ethnicity. There are limitations in the data set - it doesn't show the effect of decile review and only gives the national picture. However, since the last review happened in 2007-08, the trends are consistent enough to make few inferences.

See how the decile is calculated - Ministry of Education

Also, the effect of the last review is noticeable in the visualisation. For example, there is a significant drop in number of students at decile 7 and a corresponding increase at decile 8.

This graph shows the total number of students across deciles. The numbers have only declined for European students while rising for all other ethnicities.

Despite the drop in overall numbers, the European student population has increased significantly at the top three deciles.

The decile drift interactive shows absolute numbers because percentages obscure the rise in total student numbers at higher deciles.

The percentages are published in a separate interactive, as these highlight other interesting trends. Despite the rise in European student numbers at higher deciles, they constitute a lower percentage. This is because there are more Maori and Asian students at higher deciles as well. Overall, there has been a definite drift towards higher deciles for all ethnicities.

The chart below shows the trend overall for lower decile schools.

While for higher decile schools, the trend is reversed.

The data behind the interactive is obtained from the Education Counts website.

Data puzzles

The trends highlighted by the school roll data combined with the questions posed by the NCEA interactive show that the decile system has implications far beyond funding allocation. The questions raised in this one, combined with the decile drift visualisation and Jenson's data analysis, are the central data puzzles of the decile system.

If you think there are interesting data angles which we've missed, or not pursued - please do email us with the suggestions.