Previous work indicates that large variations in the power-law relationship, relating glacial outlet valley size to ice drainage area, may occur between different glaciological settings. In this paper, we take issue with methods used to quantify the relationships of outlet valley size to drainage area size and propose a general method for comparing power-law relationships between study areas, to determine whether or not such power-law scalings are similar. Based on this method, we demonstrate that outlet valleys have a similar sensitivity to variation in ice-contributing area irrespective of their glaciological setting, contrary to earlier findings. Minor variation in such relationships may reflect the different lithological and glaciological settings of the study sites and provide an insight into the physics of glacial erosional development of landscapes. Despite their limitations, we conclude that power-law relationships are valid and, when interpreted carefully, provide a useful basis for comparing the efficiency of glacial erosion processes in different locations.