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Revisions to data of the volume index of industrial output

Reasons for revisions to original data:

Estimation

The main reason for revisions to the data is the estimation that is used for industry 26-27. Some listed companies do no provide their data within the timetable required for the production of the statistics so their data have to be estimated. This has to be done 8 times per year. The data for January-February, for instance, are estimated. At turning points of economic trends, the estimation models react slowly to changes.

Missing data

The volume index of industrial output is based on a sample. The sample comprises some 1,000 establishments or enterprises. Every month, data are missing for an average of just under 20 establishments. This may cause revisions to the data but its impact has been quite minor.

Corrections to data

Data suppliers may correct their data retrospectively. However, as a rule these do not have a major impact at the level of total industries.

Checking of weights

In accordance with the chain index principle, establishment and industry-specific weights are changed annually. This has had some impact also at the level of total industries, although not of the same magnitude as estimation.

Calculation of annual index

The sample-based monthly volume index has been retrospectively benchmarked to the annual volume index calculated from structural statistics. This has influenced the indices especially at the 3 and 2-digit level industry categories.

Changing of seasonally adjusted figures

Seasonally adjusted index point figures may change even if original index point figures do not. The changes in the seasonally adjusted and trend point figures may also stretch several years back. Especially at turning points of economic trends seasonally adjusted series fail to react sufficiently quickly to sharp changes.

Figures become revised faster than before

Below is an example of how the original annual change percentages for January and February 2009 became revised in a few main industries.

The table shows that no appreciable revision took place in data on manufacturing exclusive of the electrical and electronics industry. Almost all of the revision comes from the electrical and electronics industry. The weight of this industry (26-27) in total industries is 20.1 per cent. At the level of total industries the bias caused by the estimation was 4 percentage points in January and 0.7 percentage points in February.

The January change percentage for manufacturing became revised downwards by just short of 8 percentage points. Exclusive of the electrical and electronics industry the data for manufacturing became revised by only 0.4 percentage points.

Revisions to data on January
Industry	1st release	2nd release	3rd release
Total industries BCDE	-22.2	-24.4	-26.3
Manufacturing C	-23.1	-25.7	-30.8
Manufacturing excl. 26-27	-27.4	-26.9	-27
Electrical and electronics industry 26-27	-10.6	-23.4	-45.4
Revisions to data on February
Industry	1st release	2nd release
Total industries BCDE	-21.3	-20.6
Manufacturing C	-22.6	-24.5
Manufacturing excl. 26-27	-25.3	-25.6
Electrical and electronics industry 26-27	-14.2	-22.2

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Last updated 8.5.2009