With the bursting of the tech bubble at the start of the 21st century, two decades of growth at the high end of the job market — once the province of college graduates with strong cognitive abilities — came to an abrupt halt, according to detailed studies of employment and investment patterns by three Canadian economists. We are still feeling the ramifications.

New evidence produced by Paul Beaudry and David A. Green of the University of British Columbia, and Ben Sand of York University, demonstrates that the collapse, between 1980 and 2000, of mid-level, mid-pay jobs — gutted by automation or foreign competition (and often both) — has now spread to the high-skill labor market.

The U-shaped pattern of job growth characteristic of recent decades – strong at the top and bottom, but weak throughout the middle — has now become “a bit more like a downward ramp,” according to David Autor, an economist at M.I.T. who documented the decline in mid-level jobs in the 1980s and 1990s.

Preliminary findings suggest that this trend is alarming in almost every respect. Just one example: the drying up of cognitively demanding jobs is having a cascade effect. College graduates are forced to take jobs beneath their level of educational training, moving into clerical and service positions instead of into finance and high tech.