2018-based Subnational Population Projections (SNPPs) - March 2020

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2018-based Subnational Population Projections (SNPPs)

Good Afternoon

The 2018-based Subnational Population Projections (SNPPs) for England are due to be released on 24 March 2020. Ahead of this, we wanted to share some information on the changes that have been made to the methodology, and what the upcoming release will look like in terms of variants produced.

We continually look for ways to refine and improve our methodology and have made several changes since the 2016-based release:

  1. Internal migration – Since the mid-2017 population estimates, ONS has used new methods for estimating internal migration, including improved accounting of moves for higher education leavers. More details on these changes can be found here. The internal migration trend used in the SNPPs is historically created from five years of past data. However, because the methods are new, we are restricted to using a trend created either from two years of past data on the new methodology, or from five years of historical data (three years from old methodology and two from the new methodology). After conducting analysis and receiving feedback, we have taken the decision to use the two-year average in the principal projection as we see this as a more robust methodology. We will also look to publish a variant which uses the five-year hybrid average, comprising data from both methodologies, which can be used for comparison with the principal projection.   


  1. Following research and analysis we have taken the decision to treat prisoners as a static population. Our research found that the general demographic composition of prisoners in England changes very little over time. As such we are adding these to the special populations of This means that the population of prisoners in each area will have a constant size, as well a constant age and sex profile over time. This is an improvement on the 2016-based method, where the prisoner population got progressively older.

The 2018-based principal SNPPs will be constrained to the principal 2018-based population projection for England, available in the 2018-based national population projections publication of 21 October. The following variants will be published alongside the principal SNPPs:

  • High migration variant (constrained to the high migration variant in the 2018-based National Population Projections)
  • Low migration variant (constrained to the low migration variant in the 2018-based National Population Projections)
  • 5-year internal migration comparison variant (this is the hybrid variant described above)
  • 10-year migration variant (this will use the actual migration estimates from the full 10 years of past data, regardless of methodological changes)

As ever, we are keen to receive your comments or feedback about our proposed changes, please email MPSD.Stakeholders@ons.gov.uk. In addition, if you have any other suggestions for the publication, please let us know.

Many thanks

Andrew Nash - Population and Household Projections, Office for National Statistics

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