Three years into the bear market, the long shadow cast by Nikolai Kondratieff has returned to haunt investors. His work has scarcely been discussed since the downturn of the early 1980s. But strategists report growing interest in his theory that economies regularly go through long cycles of expansion and contraction.

Opinions differ on when each cycle starts and ends. Back in the early 1980s, some pundits anticipated a deep Kondratieff-inspired slump which never came.