Heichel, S, J Pape, and T Sommerer. 2005. Is there convergence in convergence research? An overview of empirical studies on policy convergence. Journal of European Public Policy 12, no. 5: 817-840.
"This article reveals that there is no homogenous picture of policy convergence: Although frequently observed, empirical studies often disagree as to its extent. The representation of policy fields, geographical regions and periods analyzed differ, which makes an overall assessment of policy convergence impossible. The comparability is further constrained by differences in the operationalization and research methods applied by scholars in this field" (from abstract; 817).
The scholarship on convergence is born from a variety of schools with various interests and various approaches. These authors are interested in research projects that focus on empirical results stemming from convergence, and does not make the same set of rigorous distinctions between different kinds of convergence that Knill makes (2005). On pages 820-3 the authors list all of the studies that they explore, their issue area focus, their regional focus, the period in question and whether or not convergence was found.