Irregular migration

Data on irregular migration are mostly derived from administrative sources. Data on stocks of irregular migrants can be gleaned from applications for regularization or voluntary return programs; implementation of forced returns; detections of irregular stays in the country; and sanctions incurred by employers of undocumented migrants. Data on irregular migration flows can be gleaned from border apprehensions or refusals of entry into a country (IOM, 2022b). In general, however, numbers from administrative records should be taken with a pinch of salt as they may be more indicative of authorities’ efforts and priorities than of actual variations in irregular migration (GMG, 2017).

Population censuses and household surveys can be used to estimate the stock of undocumented migrants. For example, the Pew Research Centre uses the American Community Survey, the Census and the Current Population Survey to estimate the number of undocumented immigrants by subtracting the number of lawful permanent residents from the total number of foreign-born individuals. However, such methods are likely to underestimate irregular migration as irregular migrants may seek to avoid census interviews (IOM, 2022b). 

Some studies have used the “capture-recapture” method, whereby a hidden population is investigated based on repeated sampling of the same population, for estimating the stock of irregular migrants. However, this method assumes that the chances of getting caught are not only constant over time but also relatively homogenous across migrant groups. For a comprehensive overview of direct and indirect approaches to estimating irregular migration, see the 2008 Clandestino Project Report on Methodological issues (Jandl et al., 2008).

New initiatives tracking “mixed” migration flows are a potential source of data on irregular migration, with the caveat that irregular movements are not always clearly distinguishable from regular border crossings in free movement areas, such as those characterized by transhumance. Such efforts include IOM’s Displacement Tracking Matrix and the 4Mi methodology used by the Danish Refugee Council’s Mixed Migration Centre. IOM’s Displacement Tracking Matrix (DTM) – an information management system used to track and monitor displacement and mobility during crises – collects data on different types of population movements, including irregular migration, through Flow Monitoring Surveys (FMS) and has been active in over 60 countries since 2004. The Danish Refugee Council’s 4Mi operates through monitors stationed in urban hubs for migration or at border crossings. The monitors are trained to administer standardized surveys targeting migrants engaged in irregular movements via a smartphone. While the 4Mi is not suitable for producing quantitative data on irregular migrant stocks or irregular migration flows, it provides (non-representative) insights into the profiles, paths and protection risks of irregular migrants (Ardittis and Laczko, 2017).

The nature of irregular migration and the fact that a migrant’s legal status may be subject to frequent change makes collecting data on irregular migrant stocks or irregular migration flows more challenging (Ardittis and Laczko, 2017). An increase in irregular migration does not necessarily reflect an increase in the numbers of irregular migrants as changes to a country’s migration policies, practices and programs may lead to migrants already present in the country becoming irregular. Irregular migration sometimes overlaps with migrant smuggling, which is defined as the act of enabling the irregular entry of another person for financial or material gain (IOM, 2019. Indeed, recent estimates from EUROPOL, suggest that more than 90 per cent of irregular migrants use a smuggler to facilitate some part of their journey (IOM, 2018). Cross-country comparisons of irregular migration may be misleading due to different definitions of irregular migration, different methodologies for collecting data on irregular migration and different capacities for border control (IOM, 2022b). Furthermore, failure to provide age, gender or disability-disaggregated data on irregular migration limits an understanding of the intersecting vulnerabilities of irregular migrants (IOM, 2021a).