A second puzzle that challenges the conclusion that advances in ICT are the primary source of recent productivity gains is the observation that, over the past twenty years or so, increases in ICT investment have not been followed reliably and in short order by increases in productivity growth.
Instead, the lag between investments in new technologies and their putative productivity benefits appears to be long and variable. For example, ICT investment in the United States began in earnest in the 1980s, but productivity did not begin to accelerate until the mid-1990s.