Even when researchers control for all observable characteristics, a portion of the gender wage gap is left unexplained.In a 2016 study, economists Francine Blau and Lawrence Kahn found that the unexplained portion of the gender wage gap narrowed dramatically in the 1980s, shrinking from between 21 and 29 percent of the gap in 1980 to between 8 and 18 percent of the gap in 1989.Economists often argue that this unexplained portion, while not synonymous with discrimination, may tell us how much gender discrimination could be affecting wages.However, after 1989, the unexplained portion of the gap did not narrow any further, and it has remained stable ever since.By this measure, discrimination is either stable or increasing.