Welcome to Seasonal adjustment in Statistics New Zealand
Introduction - What is seasonal adjustment and why is it used?
Frequently asked questions - A guide to what is available, with links to questions and answers.
This section of the website was first published in February 2001. Feedback on whether it is useful, or further questions are welcome. Please use the feedback button above, or email seasonaladjustment@stats.govt.nz.
Introduction
The broad aim of studying time series of economic data is the prompt recognition of significant changes in the direction and level of economic activity.
Many time series have a recurring seasonal pattern that obscures the underlying behaviour of the series. Seasonal adjustment is the process of estimating and removing the varying seasonal effects from a time series in order to reveal non-seasonal features. Examples of seasonal effects include sales increases at Christmas and annual cycles in agricultural production. Sometimes during the seasonal adjustment process we also estimate and remove calendar effects.
The resulting seasonally adjusted series enables comparison of data for adjacent months/quarters.
Example of a seasonal time series:
Use these links to find answers to frequently asked questions about seasonal adjustment within Statistics New Zealand:
The underlying model
How SNZ computes the components X12 ARIMA
How to interpret output from seasonal decomposition
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For enquiries and information requests
This page last modified on: 20 February 2004