Inflation Adjusted HMRC Regional Trade Statistics for Scotland: Methodology

Seasonal adjustment

The CVM in this report is presented with seasonal adjustment. This is analysis which removes seasonal effects; systematic variation associated with the time of the year. This facilitates comparisons between consecutive time periods. For example, we might expect trade to go up at certain times of year (such as around national holidays), seasonal adjustment creates a model of what would have been traded had there been no seasonal affects. It does this by examining correlations between the value of trade at a particular time and the value at preceding times; past values are used to forecast future values, and in cases where high correlation is found with corresponding time periods of the same season, a term is added to the model to correct for this. 

When a change over time is presented, it includes seasonal adjustments. This is not the case for any figures presenting values of trade in a static time period, for example the value of Scotland’s goods exports in a particular year.