In other words, higher productivity growth can explain why the economy’s average growth rate is faster, but I do not think it can provide an adequate answer for why the expansion will last longer. To do this, I think a macro-economic explanation is required.
Here I have to come back to low inflation and low inflationary expectations, which have characterised the 1990s expansion, but were clearly absent from earlier expansions. As the earlier expansions matured, inflationary pressures built up which simultaneously pushed up prices (requiring a monetary policy response) and squeezed businesses and business confidence.