GDP Quarterly National Accounts: Quality and Methodology Information

Coherence and comparability

Coherence is the degree to which data that are derived from different sources or methods, but refer to the same topic, are similar. Comparability is the degree to which data can be compared over time and domain for example, geographic level.

The quarterly GDP statistics for Scotland are designed to be coherent with the equivalent statistics for the UK, in as much as the available data and methods allow. The Scottish Government uses extracts of the same data sources used by the ONS, such as surveys or administrative data, for large parts of the economy. For some industries or other components of GDP, estimates for Scotland are instead made with direct reference to the equivalent component for the UK, for example by taking an employment share of the UK total. In this way, coherence between Scottish estimates and the UK as a whole is usually high, and therefore so is comparability of outputs.

At times there can be differences due to timing lags in the introduction of new methods or data sources. Such differences are unavoidable and kept to a minimum, but users should carefully check the age and reference periods for statistics to gauge whether comparisons are being made on a like for like basis.

Since international standards such as System of National Accounts  2008 and European System of Accounts 2010 are used in the production of the UK national accounts, estimates for Scotland should also be directly comparable with the accounts of other countries, including members of the EU and OECD. However, as with the UK, issues such as differing revisions policies and different timescales for making methodology changes mean that some care should be taken when comparing statistics between different countries.

During the coronavirus (COVID-19) pandemic, methodological differences in the measurement of non-market output have led to particular challenges in the comparability of GDP between countries. Even several years after the immediate impacts of the pandemic, it continues to have an effect on the compilation of statistics, particularly with regard to the coherence and comparability of GDP over time and between places. Some of these issues were summarised in a blog by the National Statistician relating to large revisions in ONS statistics for the UK in autumn 2023, but the message is equally applicable to statistics for Scotland or elsewhere. The key message is that comparisons between different places, including between Scotland and the UK as a whole, of how GDP changed during 2020 and 2021 in particular, along with provisional measures of how GDP compare to 2019 levels, should be made with particular caution.

One issue which is pertinent to the coherence of GDP statistics for Scotland with other statistics for Scotland or other places is the simple question of what is defined as the economic territory of Scotland?

The UK Statistics Authority monitoring report on Official Statistics in the context of the referendum on Scottish Independence (2013) highlighted the importance of clearly defining what is meant by ‘Scotland’ in the production and use of statistics. The different territorial concepts available can substantially affect analysis for Scotland.

Scottish Government GDP statistics are currently reported using two main territorial concepts:

Onshore – which relates to Scotland’s land-based territory, as defined for Eurostat regional reporting purposes and embedded in the International Territorial Level (ITL) geography, which excludes any of the UK extra-regio (offshore and overseas) economic activity in Scottish waters.

Wider economic territory (including offshore) – which is the land-based territory plus the Scottish part of UK extra-regio economic territory. This consists of offshore oil and gas extraction in Scottish waters plus a population share of UK overseas territorial enclaves such as military bases, consulates and embassies.

All estimates for Scotland’s wider economic territory produced by the Scottish Government are based on the Scottish Adjacent Waters boundary, which follows the equidistant (median) lines between Scotland, England and Northern Ireland. This boundary has been adopted by the Scottish Government, HMRC and ONS in the production of some economic, trade and public sector finance statistics for Scotland. In addition, some statistics simply allocate a population share of UK extra-regio activity to Scotland, although these are not widely used.

Every effort is made to ensure that the data series we produce are comparable over time. We produce time series for quarterly and annual GDP back to 1998 which are fully comparable to the UK and other countries. Where possible, changes to methodology are applied to the whole series to ensure this comparability is maintained.

For earlier periods, a time series of annual GDP in volume terms is produced back to 1963, which is based on historical estimates projected backwards from the current quarterly data. This historical time series has had some adjustments made to it over the years to reflect revisions made to UK GDP since its original estimation, however we do not hold the data required to re-estimate it fully and it does not have the same level of quality as the statistics for 1998 onwards.