Trends in the geographic distribution of human embryonic stem-cell research

Human embryonic stem-cell (hESC) research offers substantial potential benefits but has generated politically influential controversies and, in the United States, funding restrictions. Some observers fear the United States has been falling behind nations more permissive in this field, but policy debate has remained largely anecdotal. This study reports citation data indicating that the share of hESC research publications credited to the United States in the six years following the introduction of key technologies was significantly less than in five less contentious biomedical-research areas. The United States share of hESC publications fell sharply in 2003 and remained near this reduced level in 2004. Putative explanations are reviewed and several implications discussed.