*  *  *  It is thus heightened growth of output per worker that offers the greatest potential for boosting U.S. gross domestic product to a level that would enable future retirees to maintain their expected standard of living without unduly burdening future workers. Productivity gains in the United States have been exceptional in recent years.
The labour potential, that is the number of people who are readily available to the labour market, increased greatly in these economies and they presented plenty of high-yielding investment opportunities. Both led to a significant growth in per capita income. However, the phase before the crisis was also characterised by extremely favourable financing conditions and a high propensity to take risks.