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Recent usage has distinguished human capital (the stock of knowledge
in the labor force) from
labor.\cite{samuelson_nordhaus}. Entrepreneurship is also sometimes
considered a factor of production. Sometimes the overall state of
technology is described as a factor of
production.\cite{parkinesquivel} The number and definition of
factors varies, depending on theoretical purpose, empirical
emphasis, or school of economics.\cite{friedman}

\bibliography{factors}

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