nationality category in data sets, and relevant data is not captured. Even where data sets include a “nationality” category termed “stateless”, the definition of the category is often questionable and inconsistent with the definition used in other data sets. This contributes to an absence of accurate data on the numbers and profile of stateless persons on UK territory. Thirdly, compounding this problem, stateless persons are subject to contested definitions and are consequently hard to classify or categorise. Rather than being a group for whom established legal procedures and protections exist, such as asylum-seekers and refugees, stateless persons share only the common characteristic of a lack of nationality, whatever their other circumstances. Stateless individuals can therefore span multiple incomplete data sets. Data sources and methods of analysis Stateless and “unreturnable” persons can be found amongst both documented and undocumented migrants, as well as amongst those born in the UK. Previous equivalent mapping studies have principally focused on estimating undocumented migrant populations and have predominantly taken place in Europe and North America.16 A diverse set of methodologies have focused on different approaches. Most notably, a distinction is made between “direct” and “indirect” methods. A combination of both methods was chosen for the quantitative methodology of this study. Direct methods A number of direct data sources that record numbers of persons as “stateless” or of “unknown nationality” were examined. Close attention was paid to the classification of “stateless” or “unknown nationality” used in each data source to try to ensure consistency both with the definition of “stateless person” used in this study, as well as across the different datasets. It was recognised that examining direct data could provide certain totals, but risked resulting in a significant undercount of the total population. There are no direct data sources that relate to “unreturnable” persons and this group does not exist as a separate category within any of the datasets examined. Direct data sources examined include: the Labour Force Survey; the International Passenger Survey; European Union (EU) statistics published by Eurostat; UK government published statistics; management information provided by the UK Border Agency; and data sets collected by refugee-assisting NGOs that provide services to vulnerable migrants. Indirect methods Indirect methods can be used to infer a population size by investigating data derived from the circumstances and characteristics of the population under study and, in the case of hidden populations, how their position in society becomes visible. This could include examining data sets relating to situations where stateless and “unreturnable” persons are likely to be more highly represented. Whilst this method, in contrast to the direct methods, would have the advantage of attempting to encompass hidden populations, it also has larger margins of error. 16 16 Pinkerton C., McLaughlan G., and Salt, J., Sizing the Illegally Resident Population in the UK, Home Office Online Report 58/04 London: Home Office, 2004. Mapping statelessness