Global investment in biomedical research has grown significantly over recent decades. In 2010, global investment reached US$240 billion (adjusted for purchasing power parity), delivering important health dividends to patients and citizens [1]. However, not all of this investment is distributed evenly by gender. It follows, arguably, that scarce research resources may not be optimally invested by either not supporting the best science or by failing to investigate topics that benefit women and men equitably. Gender bias in biomedical and health research involves both biological sex differences and sociocultural differences in the way women and men behave, and in the way they are treated [2]. There is evidence that gender bias in biomedical and health research can occur at all stages of the research process across the following four domains.

First, women tend to be significantly underrepresented in research both as researchers and research participants. Although in 2013, women had reached 55% of admissions to medical schools in the United Kingdom and 47% in the United States of America, they constituted only 28% of faculty physician-scientists in the United Kingdom and 38% in the United States [3]. Moreover, female faculty members tend to report less favourable experiences and feel excluded [4, 5]. Women are also underrepresented as research participants. Historical analysis demonstrated a male bias in biomedical research throughout the 20th century: it was evident in 8 of the 10 biomedical fields surveyed in 2009 [6]. For example, while women represent nearly half of people living with HIV, they are under-represented in clinical studies of HIV antiretroviral drugs (19%), prophylactic vaccines (38%) and curative strategies (11%) [7]. Women are also under-represented in high-impact studies of non-sex-specific cancers [8].

Second, female investigators tend to receive less research funding than their male counterparts in absolute and relative terms. This may occur because there are fewer women investigators who apply for research funding [9], and those who apply receive smaller awards than men [10]. There is some evidence that, in certain settings, this is also amplified by reported nepotism and sexism in peer-review [11]. Although an earlier meta-analysis of empirical studies from different fields concluded that women applying for grants have statistically significant lower odds of receiving funding than men by approximately 7% [12], a more recent and methodologically advanced meta-analysis of the same data [13] and a recent empirical study [14] concluded the contrary. United States research suggests that female early career researchers receive significantly less start-up support from their institutions [15] and are significantly less likely than men to achieve independent funding awards [16]. Further, United States research suggests that women at particular career stages are less likely to apply for the competitive grants for which they are eligible, compared to their male counterparts [17]. Research from the Netherlands demonstrated gender bias favouring male grant funding applicants in the evaluation of the ‘quality of researcher’, but not the ‘quality of proposal’ [18]. Even in the fields where there is no difference in funding rates between the genders, such as radiology, women have less total grant funding than men [19].

Third, women tend to appear less frequently than men as winners of prestigious scientific awards and as authors of research publications. Among 210 Nobel Laureates in Physiology or Medicine awarded from 1901 to 2015, there are only 12 (5.7%) women [20]. Despite significant progress in recent decades, women are still underrepresented as authors of research articles in medical journals [21, 22], especially as first and senior authors [23, 24]. For example, the proportion of women first authors in six prominent international medical journals increased from 6% in 1970 to 29% in 2004, and the proportion of women senior authors increased during the same period from 4% to 19% [23]. In radiology, the proportion of women first authors increased from 8% in 1978 to 32% in 2013 [25]. The proportion of women first authors in high impact general medical journals increased from 27% in 1994 to 37% in 2014, but it has recently plateaued and even declined in some journals [26].

Finally, women may be disadvantaged as the beneficiaries of research in terms of its health, societal and economic impacts [27–29]. There is evidence to suggest that research that does not account for gender differences can result in inaccurate conclusions about how women respond to disease and this, in turn, will influence the effectiveness of treatment choices [30, 31]. For example, ‘Yentl syndrome’ describes sex bias in the management of coronary heart disease due to the fact that medical research had predominantly studied symptoms of heart attacks in men [32]. Historically, those women who presented with symptoms of heart attack similar to those in men received the same diagnostic and treatment procedures as men, but those whose symptoms presented differently were not properly treated and may have died unnecessarily. For such reasons, the League of European Research Universities has recently stressed that, without including gender analysis in research, the impact of science may not be equally beneficial for both men and women [33].

In what follows, we elaborate on the path dependent nature of gender bias in science and why it is difficult, but not impossible to address. Second, we outline key characteristics of research impact assessment; we argue that by investigating gender bias, research impact assessment can become a force for good in moving science policy and practice towards gender equity. Third, we offer a set of recommendations about how research funders, research institutions and research evaluators can include and strengthen analysis of gender equity in research impact assessment. We conclude by issuing a global call for action.