In quantitative analyses, we analyse nominal and continuous variables, or so we are taught. For example: is a country democratic and how democratic is a country, or is a person poor and how poor is she? But both democratization and impoverishment are processes that develop over time. In consequence, there are social trajectories of democratization and impoverishment. Sequence analysis, originally developed in biology to analyse DNA sequences, is a longitudinal method that allows to analyse such trajectories, or sequences of different states in a life course, different states in a country's development or any other sequence of interest.
Aisenbrey & A. E. Fasang (2010). ‘New Life for Old Ideas: The ”Second Wave” of Sequence Analysis Bringing the ”Course” Back Into the Life Course’. Sociological Methods & Research 38(3):420–462.