GDP per capita is correlated with productivity, measured in terms of kg of product per animal
per year, for both chickens and pigs (Fig 1)
Fig 1. Productivity (kg of meat per animal per year) as a function of Gross Domestic Product per
capita (USD in purchasing power parity in 2010). Each dot represents a country, with the size indicative of
the stock according to FAOSTAT [5]. Only countries with stocks > 0 for chickens (n = 190) and pigs (n = 170)
are included.