Vienna Yearbook of Population Research 2021 (Vol. 19), pp. 1–22 Mortality evolution in Algeria: What can we learn about data quality? Farid Flici 1,∗ and Nacer-Eddine Hammouda 2 Abstract Mortality in Algeria has declined significantly since the country declared its independence in 1962. This trend has been accompanied by improvements in data quality and changes in estimation methodology, both of which are scarcely documented, and may distort the natural evolution of mortality as reported in official statistics. In this paper, our aim is to detect these methodological and data quality changes by means of the visual inspection of mortality surfaces, which represent the evolution of mortality rates, mortality improvement rates and the male-female mortality ratio over age and time. Data quality problems are clearly visible during the 1977–1982 period. The quality of mortality data has improved after 1983, and even further since the population census of 1998, which coincided with the end of the civil war. Additional inexplicable patterns have also been detected, such as a changing mortality age pattern during the period before 1983, and a changing pattern of excess female mortality at reproductive ages, which suddenly appears in 1983 and disappears in 1992. Keywords: mortality; Algeria; Lexis map; data quality; methodological change; vital statistics 1 Introduction Mortality analysis remains a common approach to assessing the efficiency of public health programs (Purdy et al. 2013) and related improvements in the living conditions of a given population (Elo and Preston 1992). The quality and validity of such analyses relies to a large extent on the quality of the underlying data, which is often far from perfect in the context of developing countries. Thus, whenever 1 Research Center in Applied Economics for Development (CREAD), Algiers, Algeria. 2 National Committee for Population, Health Ministry, Algiers, Algeria. ∗ Correspondence to: Farid Flici, farid.flici@cread.dz https://doi.org/10.1553/populationyearbook2021.res1.3