<P> The economic growth rate is calculated from data on GDP estimated by countries _́ statistical agencies . The rate of growth of GDP / capita is calculated from data on GDP and people for the initial and final periods included in the analysis . </P> <P> In national income accounting, per capita output can be calculated using the following factors: output per unit of labor input (labor productivity), hours worked (intensity), the percentage of the working age population actually working (participation rate) and the proportion of the working - age population to the total population (demography). "The rate of change of GDP / population is the sum of the rates of change of these four variables plus their cross products ." </P> <P> Increases in labor productivity (the ratio of the value of output to labor input) have historically been the most important source of real per capita economic growth . "In a famous estimate, MIT Professor Robert Solow concluded that technological progress has accounted for 80 percent of the long - term rise in U.S. per capita income, with increased investment in capital explaining only the remaining 20 percent ." </P> <P> (Note: There are various measures of productivity . The term used here applies to a broad measure of productivity . By contrast, Total factor productivity (TFP) growth measures the change in total output relative to the change in capital and labor inputs . Many of the cited references use TFP .) Increases in productivity lower the real cost of goods . Over the 20th century the real price of many goods fell by over 90% . </P>

Explain the importance of productivity improvements for economic growth
find me the text answering this question