This paper studies convergence in per-capita GDP across European regions over the period 1980-2000. The authors use median unbiased estimators of the rate of convergence to the steady-state growth path, while allowing for unrestricted patterns of heterogeneity and spatial correlation across regions.
Link
ftp://www.ceistorvergata.it/repec/rpaper/No-58-Meliciani-Peracchi.pdf