Dear Jascha,
There is a pdf document called “Understanding Society Innovation Panel Geographical Lookup Tables”, which is available at https://discover.ukdataservice.ac.uk/catalogue/?sn=6916, and describes in a relatively basic way how the geographies have been arrived at. They are calculated using postcodes supplied by users using lookups against the official ONS Postcode Directories – no further manipulation of the lookups are made by Understanding Society, so what is in the relevant Postcode Directory is what is used. From wave 6 (of the main survey), where possible, the Postcode Directory closest to the centre point of the survey is used and any deviation from that methodology is identified in that document. Deviations are only made where, for example, a particular field is not available in the relevant directory for that year or if a field format has changed. It is important to realise that the Postcode Directory is an ONS document so any changes to postcodes, boundaries etc. are in their hands and not ours. Each Postcode Directory is provided by the ONS with its own user guide and there are various ONS and other organisations papers that discuss boundary changes etc.
So, to answer your first question, yes, theoretically this is possible. It is also theoretically possible that a postcode might not change but is re-allocated to another LAD. As mentioned above, this is not within our control.
Regarding your second question, Understanding Society uses the oslaua field in the ONS Postcode Directory for the Local Authority. According to the ONS Postcode Directory User Guide it is defined as “The current LAD/UA to which the postcode has been assigned”. Although the ONS Postcode Directory User Guide does not say so we would assume that if the 2014 LAD was available then that is what was used and that for directories predating the 2014 LAD then it couldn’t be used. Currently, with our present methodology we do not need to do anything to handle changes in LAD boundaries. This is, however, an area that we will revisit in the future to see whether users might benefit from additional geographical information that might help with the sorts of issue that your query implies.
Best wishes,
Stephanie Auty - Understanding Society User Support Office
Updated by Stephanie Auty