How to read a Lexis surface

This is an excerpt from Schöley, J., & Willekens, F. (2017). Visualizing compositional data on the Lexis surface. Demographic Research, 36(21), 627–658. https://doi.org/10.4054/DemRes.2017.36.21

Lexis surfaces show the development of a demographic indicator over two time dimensions simultaneously. Often, the time axes are historical period or birth cohort in conjunction with age allowing for the visual display of age, period, and cohort effects. These effects can readily be seen on the Lexis surface of mortality rate sex ratio in England & Wales (see below).

Shown is the ratio of male to female death rates across age and since the mid 19th century. The excess male mortality resulting from military deaths during the first and second world war leaves a trail on the Lexis surface in the form two vertical bands of deep blue colour – a classic example of a period effect where a cross-section of the population is affected by an historical condition. But we also see an interaction between period and age: The high levels of excess male mortality during the wars are limited to the age range of men in active military service. Starting in the mid-1950s we observe the emergence of excess mortality among young men. This age effect is visible as a horizontal corridor of deep blue colour and can be traced back to the effective prevention and treatment of infectious diseases which in turn put more emphasis on the more male dominated accidental deaths in early adulthood (Gjonca2005). The diagonal colour pattern around ages 50--80 and years 1950--1980 marks a cohort effect and can be traced back to those born at the end of the 19th and the beginning of the 20th century. The rising popularity of smoking among men took its toll later in life in the form of lung-cancer. Women of the same cohorts smoked less than men and therefore gained a survival advantage. This advantage vanished once women took up smoking as well (Preston2006, Beltran-Sanchez2015).

[Gjonca2005]: Gjonça, A., Tomassini, C., Toson, B., & Smallwood, S. (2005). Sex differences in mortality, a comparison of the United Kingdom and other developed countries. Health Statistics Quarterly, 26, 6–16.

[Preston2006]: Preston, S. H., & Wang, H. (2006). Sex mortality differences in the united states: The role of cohort smoking patterns. Demography, 43(4), 631–646. https://doi.org/10.1353/dem.2006.0037

[Beltran-Sanchez2015]: Beltrán-Sánchez, H., Preston, S. H., & Canudas-Romo, V. (2008). An integrated approach to cause-of-death analysis: Cause-deleted life tables and decompositions of life expectancy. Demographic Research, 19, 1323. https://doi.org/10.4054/demres.2008.19.35