  Resilience, the ability to recover from adverse events ("shocks"), is of
fundamental importance to food security. This is especially true in poor
countries, where basic needs are frequently threatened by economic,
environmental, and health shocks. An empirically sound formalization of the
concept of food security resilience, however, is lacking. Here we introduce a
general framework for quantifying resilience based on a simple definition: a
unit is resilient if $(a)$ its long-term food security trend is not
deteriorating and $(b)$ the effects of shocks on this trend do not persist over
time. Our approach can be applied to any food security variable for which
high-frequency time-series data is available, can accommodate any unit of
analysis (e.g., individuals, households, countries), and is especially useful
in rapidly changing contexts wherein standard equilibrium-based economic models
are ineffective. We illustrate our method with an analysis of per capita
kilocalorie availability for 161 countries between 1961 and 2011. We find that
resilient countries are not necessarily those that are characterized by high
levels or less volatile fluctuations of kilocalorie intake. Accordingly, food
security policies and programs will need to be tailored not only to welfare
levels at any one time, but also to long-run welfare dynamics.
