UNHCR STATISTICS TECHNICAL SERIES: 2019/1 statelessness determination, potentially leading to an increased risk of underreporting numbers of stateless persons. These factors alongside other inconsistencies underscore the need for better guidance on enumeration and reporting methods most conducive to monitoring figures on stateless populations for reduction and prevention of statelessness. In 2018, 55 of 78 reporting countries disclosed figures derived exclusively from government sources. Data collection methods used include 34 administrative registers, 9 national censuses, 5 government estimates, 2 household surveys, 2 statelessness determination procedures, and 3 unspecified methods. Whereas the majority of UNHCRassisted reports cite populations of undetermined origin, governments focus on reporting de jure and de facto stateless populations. Reporting countries from 2018 cited 16 de jure stateless populations, 12 de facto stateless populations, 12 undetermined populations, 7 combinations of de facto stateless and undetermined populations, and 8 combinations of de jure stateless and undetermined populations. Across time, however, methodological changes and improvements in reporting are not always documented amid population fluctuations, reporting gaps, irregular figures and other uncertainties. It is often difficult to assess whether year-on-year changes in stateless numbers correspond to real population fluctuations or to changes in the methodology. Population changes may correspond to unexplained and later reversed methodological decisions, such as alterations in government source. Annually adjusted figures may take into account naturalization processes but base adjustments on decade-old figures that do not account for demographic change. Despite lack of methodological elaboration accompanying historical methods and changes, some of the variation in the data can be explained by looking at metadata such as the population type and supplementary comments. Government Registration With 34 of 78 reporting countries in 2018 citing government registration data, administrative registers are the most common and at the same time among the most methodologically heterogeneous bases for government reporting. Although the following list is incomplete, frequently cited government authorities include Ministries of the Interior, Departments of Immigration and National Statistical Offices, with the latter being the most common. Less frequent sources include Police and Border Control, Ministries of Justice, and dedicated offices. Similar national departments nonetheless exhibit a wide range of methods for data collection and reporting: While statistical offices often rely on data from tax authorities, others consolidate information across numerous sources and do not report registration data. Immigration departments may report to-s statistical bureaus, which subsequently report to UNHCR; a process which may involve unspecified adjustments. Thus, figures from government authorities neither correspond solely to registration data nor particular statelessness categories. In our dataset, at least 20 of 35 countries citing government registers in 2018 have done so consistently since 2009. However, there persists a lack of centralized data collection and verification procedures. While some countries cite figures based on municipal data, others do not verify self-reported data and classify statelessness as a phenomenon exclusively linked to specific ethnic groups. Doing so can lead to exclusion and underreporting where there are other stateless groups in the country. 5 UNHCR / October, 2019