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Occasional Paper

Modelling Census Under-Enumeration - A Logistic Regression Perspective

Summary

Inevitably, not everyone in Scotland was enumerated in the 2001 Census. In Scotland, as in the rest of the UK, the raw Census figures were adjusted to compensate for the differential levels of under-enumeration that existed between different age-sex groups and areas. This was achieved by the One Number Census project which produced an individual level Census database, with synthetic individuals used to fully adjust for the differential levels of under-enumeration. Census under-enumeration stems from a wide variety of factors – for example demographic, socio-economic and household composition.

An accurate identification and measurement of under-enumerated people allows the implementation of initiatives to maximise coverage. For example new designs of the census form can be trialled in households most susceptible to under-enumeration with the aim of making it easier to complete.

Therefore this paper seeks to model under-enumeration, by ascertaining the underlying characteristics of under-enumerated areas, determined using the non-response rates. These characteristics are found via logistic regression modelling. Logistic regression analysis controls for all variables simultaneously during modelling and can therefore reveal which factors are significant predictors of the outcome variable in question.

The results of the series of logistic regression models show that there are a variety of factors that affect under-enumeration. However, from a strategic viewpoint, an area will be susceptible to under-enumeration if it has a disproportionate number of people who are transient and/or deprived. The deprivation characteristics are income and health deprivation, non-car ownership, overcrowding and multi-occupancy. The transient characteristics are single (never married), young people (aged 25-29), living in privately rented accommodation and working in intermediate occupations. Some people – some single mothers, for example – could be construed as being both transient and deprived.