National Records of Scotland

Preserving the past, Recording the present, Informing the future

2001 Census Variables

2001 Census Variables

2. The Processes Analysed

An Edit and Donor Imputation System (EDIS) was devised for 2001 and applied to individual records. It was designed to fill in all the gaps in records for existing people and households, except for the voluntary questions on religion. EDIS contained five components.

  • Multi-tick rules where more than one box was ticked but only one option was allowed.

  • Range checks to prevent answers being outside an acceptable range.

  • Filter rules to resolve some inconsistencies and to decide which fields should be set to 'No Code Required' where questions were answered but should not have been.

  • A set of Edit rules to deal with missing items or responses which appeared to be in error or inconsistent when compared with other data. Edit either set a specific value or left it to Imputation to determine a value.

  • All items which were missing after the Edit stage were dealt with by the Imputation component which searched for a similar person or household (the donor) whose values would be copied into the records containing missingness (the recipient). A series of criteria were drawn up to determine what was meant by ‘ similar’. A suitable selection of variables (Primary Matching Variables) was defined to match on for each missing item. Rules were set up to cope with recipients with several missing items. There were also rules to ensure that each donor was not re-used too frequently.

The first two checks generally inserted a ‘placeholder’ value for the variable indicating that a proper value should be imputed at the 5th process. The 3rd and 4th processes may do one of the following:

  • replace a value supplied by the form filler with another;

  • insert a value when one was not supplied.;

  • replace a value supplied by the form-filler with a ‘placeholder’ for subsequent imputation; and

  • for the relationship within household variable, where an item failed checks of consistency with other items such as age, sex, and marital status, it may be reversed (e.g. 'parent' changed to 'child') to see if the checks were then satisfied. If so, the reversed relationship was inserted into the record; if not, it was replaced with a 'placeholder' for subsequent imputation.

A general rule was that to remove inconsistencies between variables, the minimum number of such changes should be made. One deviation from this rule was in the case of relationship where any changes to related items such as age, sex and marital status were made before relationship was checked.

The One Number Census (ONC) process estimated the number and characteristics of households and persons missed in enumeration and added records to the Census database accordingly. Some person records were added to otherwise enumerated households. Others were part of wholly added households.

Excluded from the analysis is any editing carried out to restore values originally supplied by the form-filler e.g. by faulty scanning of Census forms, or faulty coding. This analysis concentrates on measuring the extent to which the output database differs from the data supplied on forms.