Higher farm and manufacturing productivity associated with refrigerated exports led to New Zealand's attainment of the world's highest Human Development Index in 1913. Local responses to export opportunities increased the social depth of land ownership and fostered intensive growth. Closer settlement meant that land-related income gains spread widely, but land market volatility also created instability. New Zealand had the world's highest GDP per capita in 1938, but it experienced long swings in its growth rates. Dramatic swings in rural land market activity engendered by the pastoral boom contributed greatly to a long depression in the 1920s; subsequently a new monetary regime facilitated fast recovery.