The Industrial Production Index is based on input data from three different sources. The majority of the industries are calculated with information on deliveries, which corresponds to roughly 95 percent of the total added value. The conversion of delivery information into constant prices is done using the Producer Price Index, (PPI). Calculations for other industries are based on information about quantities produced and also the number of hours worked.
Information about deliveries is collected through a monthly online questionnaire sent out to approximately 2 300 enterprise units. The survey's response rate is 80-85 percent, while the weighted response rate (where the size of deliveries for the responding companies is also considered) amounts to more than 90 percent.
All time series use 2005 as the reference base period. All monthly comparisons are based on working day adjusted and seasonally adjusted index values. Seasonal adjustment means making the corrections for the seasonal variations that reappear from year to year. The purpose is in part to show those changes that are not dependent on seasonal variations and thus can allow for comparisons with other months, and in part to study evident trends. Annual comparisons are only revised for calendar effects.
When the Industrial Production Index for a new month is published, the index for previous months is also revised. The material is normally revised for five months retroactively. This is mainly due to new and revised information that has been received. Seasonally adjusted figures and trend figures are always revised from January 2000 onwards.
When seasonally adjusting the Industrial Production Index, every series is individually seasonally adjusted using the TRAMO-SEATS program. TRAMO-SEATS was introduced in 2004 for the Industrial Production Index and is recommended by Eurostat for seasonal adjustment of official statistics.
An important part of this method is to identify a model for the actual time series for each industry. These models are used for forecasts of the actual Industrial Production Index for two years forward and the forecasts are used in the seasonal adjustments. Because the forecasts are completely dependent on the choice of the model, this may cause revisions of seasonally adjusted data to a greater or lesser extent. To reduce the effects of revisions in seasonally adjusted data, Statistics Sweden has chosen to follow Eurostat's recommendation to use fixed models during the period of one year. According to Eurostat recommendations, seasonal adjustments should be reviewed at least once every year, including the selection of models. This recommendation has been applied to the Industrial Production Index since 2004.
Review of the model
The latest model review was conducted in connection with the publishing in February 2011 concerning data for December 2010. The next review of the model is planned to take place in connection with the publishing concerning December 2011.
For international comparisons, please refer to Eurostat:
Eurostat, Short-term business statistics