Perceptual thresholds vary by listener but share common ordering

Evidence

The changes from fused to separate and from beats to rough to smooth are shown hashed in Figure 2.7 to indicate that there is no exact frequency difference at which these changes in perception occur for every listener. However, the approximate frequencies and order in which they occur are common to all listeners, and, in common with most psychoacoustic effects, average values are quoted that are based on measurements made for a large number of listeners. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 576