The Research Outputs Database (ROD) has been used to investigate the effects of different input variables, including the numbers of funding bodies, on the impact of research papers in a biomedical subfield (gastroenterology). This was determined by the medium-term impact of the journals in which they were published. It was shown that, when account was taken of the effects of the other input factors, the mean impact for a group of papers increased with the number of authors, the type of research (basic more than clinical), and with the number and identity of the funding bodies. However it decreased slightly if there were more addresses; whether the paper was multinational had no significant effect. Previous work showing that multi-institution or multi-country papers are more highly cited reached this conclusion because it did not take into account the confounding effect of multiple funding sources, and possibly other factors.