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Index of Services Time series methods


This page is currently under review as part of the GDP Output Improvement Programme (277.8 Kb Pdf) .

The Index of Services (IoS) is constructed within a computerised system known as the Central Shared Database (CSDB).

This computer system incorporates the functions that operate upon the input data in order to produce the output indices.

Some of these functions are simple mathematical calculations such as adding, multiplying and dividing.

Some are more complex statistical functions, used to perform specialised tasks upon the data.

In this section the main statistical functions in the Index of Services computer system are described.

In general terms, the IoS system consists of the following processes:

  1. Receive input data
  2. "Add" turnover data quality adjustments, if any
  3. Forecast data to current processing month (if not already there) and, if data are not  monthly, three periods ahead
  4. Where monthly data are not available but are required at this level (eg where data  of different periodicities need to be combined), interpolate a monthly path
  5. "Deflate" current price turnover data with price deflator
  6. "Index" the data by rebasing to 2005=100
  7. "Weight" data series together to form SIC 4-digit groups
  8. Seasonally adjust the group level aggregate data series
  9. "Add" National Accounts annual balancing adjustments, if any
  10. If data are not monthly, interpolate a monthly path
  11. Aggregate data series together using chain-linking to form SIC 2-digit divisions
  12. "Add" data quality adjustments, if any
  13. "Add" National Accounts quarterly balancing adjustments, if any
  14. Benchmark the monthly data to the equivalent quarterly series in GDP(O)
  15. "Constrain" any data outside the National Accounts revisions window to equal  previously published values
  16. Aggregate data series together using chain-linking to form published aggregates

Simple functions are marked as " and are explained in more detail in the section on Index construction.

Functions in bold type are more complicated statistical functions. These are the 'black boxes' within the automated system.

Here the black boxes are opened up to show what goes on inside.

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