IOS quality and revisions

Details of quality and revisions for the Index of Services.

Results, particularly for the latest Index of Services (IOS) quarter, are provisional and subject to revision as more up to date information becomes available. It is normal practice for IOS estimates to be revised.

Revisions to IOS estimates

These revisions will occur primarily in light of:

  • late responses to surveys and administrative sources
  • where cross survey congruence checks provide more accurate data - for example, data can be revised back for up to four quarters and finalised once comparisons have been made with the current year Annual Business Inquiry (ABI) returns
  • where there are revisions to seasonal adjustment factors which are re-estimated every quarter

Very few statistical revisions arise as a result of ‘errors’ in the popular sense of the word. All estimates, by definition, are subject to statistical ‘error’ but in this context the word refers to the uncertainty inherent in any process or calculation that uses sampling, estimation or modelling.

Most revisions reflect either the adoption of new statistical techniques, or the incorporation of new information, which allows the statistical error of previous statements to be reduced. Only rarely are there avoidable ‘errors’ such as human or system failures, and such mistakes are made quite clear when they do occur.

Revisions Triangles

Historically, the IOS bulletin has contained information on Revisions Triangles. These triangles presented a summary of the differences between the first estimates of growth published and those published 3 years later for the same reference period.

A statistical test has been applied to the average revisions to growth to find out if it is statistically significantly different from zero. This quarter we have moved to publishing on a SIC07 basis.  As the coverage of the Index (and the broad industry groupings) is different between SIC03 and SIC07 it is not possible to compare the results provided in this bulletin with those published in July 2011.

This quarter the data for Q1 2011 and earlier have been converted to approximate the SIC07 coverage and are therefore not strictly revisions. As a result no Revisions Triangles are available this quarter. Further information on the construction of SIC07 revisions triangles will be announced in due course.

Quality and revisions

A  detailed Index of Services revisions policy which outlines the treatment of planned and unplanned revisions and quality report are available.