It is important for users to realise that not all census records have survived. This especially true for 1851 and 1861 wherein some cases data for whole parishes or even Registration Sub-Districts is ‘wanting’. Further details on missing data is available from both The National Archives and FindMyPast websites, as follows:
In addition, users are referred to a paper by Bennett, van Lieshout and Schürer which estimates the levels of missing data in the I-CeM data collection, together with ‘weights’ that have been calculated to ‘correct’ for missing data when undertaking analyses at a national level.
A further problem exists in the identification of missing census records at the level of the parish. As part of the I-CeM project, an attempt was made to reallocate each individual census record to the census parish in which it was enumerated.
This process is known as reconciliation. Whilst this sounds like a straight-forward exercise, it proved to be laborious and time-consuming and can never be exact due to the census information available that underpins this process.
In short, in order to allocate each page of the census data to an administrative parish, the I-CeM project team had to rely on the transcribed information at the head of each census page, which is non-standard, imprecise and sometimes incorrect. Despite this, each census record was allocated a parish identifier (PARID, see Data Dictionaries section below). The table below shows the difference between the population of parishes found in the raw I-CeM data following reconciliation, and what one would expect from the published Census Reports.
Subsequent to the release on the I-CeM data via the UK Data Service, a number of corrections to the PARID allocation have been made for parishes in England and Wales. These corrections can be implemented by downloading the following look-up tables.