Final answer:
The changing age structure of the population and increased efficiency in labor markets, as well as skill-biased technological change and globalization, are likely contributors to the decline in the natural rate of unemployment between the 1970s and the 2000s.
Step-by-step explanation:
The decline in the natural rate of unemployment between the 1970s and the 2000s might be the result of various factors, including the changing age structure of the population, advancements in technology, and increased efficiency in the labor markets.
During the 1970s, the U.S. saw a period of decelerating productivity growth, leading to a rise in the natural rate of unemployment as wage increases did not adjust immediately to the reduced growth in productivity, leading to lower demand for labor at higher wage levels. On the other hand, in the late 1990s, there was an unexpected increase in productivity growth which shifted the demand for labor out to the right, causing temporarily low unemployment rates, even below the natural level of unemployment.
Factors such as skill-biased technological change, globalization, and the age distribution of the population, along with changes in human capital and labor productivity, play significant roles in influencing the natural rate of unemployment over time.