In the September quarter of each year Stats NZ make changes to improve quarterly gross domestic product data.
Here is a statement from Stats NZ's recent release: "In 2017, we analysed and reconciled an extra year of national accounts data. We now have a comprehensive view of the economy and the goods and services flows up to the March 2016 year. This sees our national accounts statistics reflect a more up-to-date structure of the economy.
It also allows us to introduce an additional two years of annual benchmarks to our quarterly GDP estimates series this year. Quarterly GDP is a comprehensive suite of short-term indicators that allow us to translate the more historical view of the economy into a quarterly basis and provide contemporary insight into economic growth. "
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