Female applicants for grants from the National Institutes of Health received on average only 63 percent of the funding that male applicants received, according to a new study by the Rand Corporation.

The study -- sponsored by the National Science Foundation and ordered by Congress -- looked at other funding agencies as well and did not find similar gender gaps at the NSF or the Department of Agriculture. The NIH, however, provides much more research support than those agencies.

About one-third of the gender gap at the NIH comes in the very largest grants. But even when those grants are removed -- and adjustments are made for factors such as applicants' ages, institutions, and type of funds sought -- a gap remains. When all of those factors are controlled for, female applicants receive about 83 percent of what male applicants earn, the report found.

The Rand study also found a gap of 20 percent between women and men who apply for an NIH grant -- successfully or unsuccessfully -- and then apply again in the next two years. The comparable gap at the NSF was only 5 percent.

The study cautioned that "important data limitations" prevent full analysis of the statistics. The NIH, for example, does not have demographic information on co-investigators. So women who are on teams led by men are not accounted for. In addition, the NIH did not have information about the size of funding requests, or the research rankings of applicants' universities.

The NIH should seek more information about its applicants, the report urged, so that better analysis could identify any gender-related issues in the grants process.