Some researchers argue that the overall standard of living increased d

Some researchers argue that the overall standard of living increased during the 1920s. In general, holding constant all other factors that might impact it, economists are careful about connecting an increase in the standard of living to

(a) increases in the amount of labor used in production processes.
(b) new inventions being made in research laboratories.
(c) increases in the output of goods and services per worker.
(d) the discovery of new sources of gold and silver.

ANSWER

(c)