Alejandra Rodríguez-Sánchez Alejandra Rodríguez-Sánchez Jasper Tjaden Jasper Tjaden University of Krems Press 2025 Key points • This chapter builds on Rodríguez-Sánchez and Tjaden (2023), who reviewed the main methods for estimating irregular migrant stocks and flows, spanning both established and more experimental approaches. • Measuring irregular migration remains a fundamental challenge: the population is difficult to observe, and even widely used methods such as residual estimation or capture–recapture provide only partial pictures. • Traditional techniques continue to form the backbone of the field, but improvements have often come from incremental innovations, such as using mortality data to refine life-course approaches, or expanding residual methods with large government databases and machine learning. • More novel directions, such as exploiting consular registers, driver’s licence data, or online search behaviour, show promise in filling gaps, though these remain context-specific and experimental. PDFDocument eng 2025-09-30T07:36:51.405032Z 2025-09-30 Estimation methods Irregular migration stocks and flows Innovative data sources 1559893 b application/pdf http://creativecommons.org/licenses/by-nc/4.0/