However, as already pointed out by Depasquale and Stange (2016), such cross-sectional analyses face constraints in that licensure practices may correlate to other state-level characteristics that influence migration. This in turn would produce biased results. Nevertheless, such studies have provided the foundation, paving the w'ay towards further exploration of the impact licensing can have on labour mobility. This is consistent with the works of Pashigian (1979) and Kleiner et al. (