Activities that improve human capabilities [can be divided into] five major categories: (1) health facilities and services, broadly conceived to include all expenditures that affect the life expectancy, strength and stamina, and the vigor and vitality of a people; (2) On-the job training, including old-style apprenticeship organized by firms; (3) formally organized education at elementary, secondary and higher levels; (4) study programs for adults that are not organized by firms, including extension programs in agriculture; (5) Migration of individuals and families to adjust to changing job opportunities.

p. 9 - "Investment in human capital," 1961