American joblessness has plummeted to its lowest level since the 1960s, leaving monetary policy makers and economists alike wondering if wages could suddenly jump higher.

State-level data suggest that even when unemployment falls to exceptionally low levels, wages continue to rise only gradually, Sylvain Leduc, Chitra Marti and Daniel Wilson write. That result contrasts with a common finding that - at least at a state and local level - pay rates climb more aggressively once joblessness dips below a certain threshold.

Why the difference? It’s partly because the researchers used a statistical method that aims to zoom in on changes in the unemployment rate that are driven by labor demand, rather than by supply. Their analysis suggests that for a given drop in joblessness, wages will rise by about the same amount - regardless of how low the unemployment rate is to start with.

U.S. wages have been on the uptick. Average hourly earnings rose 3.2% last year, matching the fastest pace since 2009.

“There is no indication of any steepening in the slope as unemployment rates fall below 4 percent,” the researchers write. “Given the historical experiences of states in recent decades, we do not foresee a sharp pickup in wage growth nationally if the labor market continues to tighten as many anticipate.”