Revisions are generally defined as any change in the value of a statistic that is already published. These may include regular or one-off changes to items of data related to certain statistical processes (e.g. indices, national accounts, etc.). Revisions are necessary where amendments or additions to input data occur after their initial release, or due to changes in concepts, classification or methodology that may be brought about for a variety of reasons. Restructuring actions present an opportunity to add multiple underlying sources of revisions at the same time (e.g. changes in methodology, base period, etc.). Revisions do not include corrections to errors in production, which are addressed specifically according to the nature and scale of the correction.