In attempting to compare doctoral times-to-completion and completion rates for institutions in different countries, it was found that issues of definitions and data availability are major stumbling blocks. National and institutional contexts also complicate matters. Because of these complications, comparisons are difficult to make, but it might be possible to account for these confounding issues to gain some insights from such comparisons.
Hall, F., Evans, B., & Nerad, M. (2006). Feasibility of International Comparisons of PhD Program Time-to-Degree and Completion Rates. Unpublished article.
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