格伦菲尔德 (1950) 投资数据¶

Number of observations - 220 (20 years for 11 firms)

Number of variables - 5

Variables name definitions::

    invest  - Gross investment in 1947 dollars
    value   - Market value as of Dec. 31 in 1947 dollars
    capital - Stock of plant and equipment in 1947 dollars
    firm    - General Motors, US Steel, General Electric, Chrysler,
            Atlantic Refining, IBM, Union Oil, Westinghouse, Goodyear,
            Diamond Match, American Steel
    year    - 1935 - 1954

Note that raw_data has firm expanded to dummy variables, since it is a
string categorical variable.