Imagine you are a successful filmmaker in Hollywood. You are planning to make a big-budget action-thriller film, packed with explosions, car chases and shoot-outs. Your next step is to generate a short list of actors to consider for the lead role. What names come to mind?

Most people immediately imagine the likes of Dwayne “The Rock” Johnson, Tom Cruise or Ryan Reynolds. In other words, male actors. This is because “action-thriller heroes” are generally associated with stereotypically male characteristics. When people picture candidates for these roles, men more readily fit the bill.

Film isn’t the only industry to suffer from this bias. Science, technology, engineering and mathematics (STEM) fields and leadership positions at top organizations are notoriously male-dominated, even as these same organizations proclaim their commitment to diversity.

One problem is that, despite an organization’s public promises, cognitive biases seep into all types of decision-making, including recruitment choices. My and my colleagues’ research, published in the journal Nature Human Behaviour, looks at the informal recruitment process. Specifically, we examine the informal short list: the initial list of candidates for a role. This list typically includes candidates that are top of mind—your mentor’s new protégé, that employee who stood out in last month’s meeting, the referral from Uncle Joey—and in male-dominated industries, more often than not, they’re men. Our research proposes a seemingly simple solution to this problem: make the informal short list longer.

In an initial set of studies, we asked 858 college students and other adults to engage in the Hollywood filmmaker thought exercise described at the beginning of this article. We asked participants to generate a short list of three actors they would consider for the lead role. We then asked them to extend their initial list by adding three more names. We found that whereas the initial lists contained a women-to-men ratio of about 1:8, the extended ones contained a women-to-men ratio of about 1:6, or a 33 percent increase in female candidates (all ratios reported are rounded). We call this increase the longer short list effect.

We found similar results in two more studies set in the technology industry. Across studies, we recruited 265 people with a background in the field and asked them to imagine they were consulting for a tech start-up in California that was looking for a new CEO. The participants were asked to propose a list of three potential candidates for the company to consider and then told to expand the list by adding three more names. We found that whereas the initial list contained about a 1:6 women-to-men ratio, the ratio in the extended list was about 1:4, or a 44 percent increase in female candidates.

What explains this? The longer short list effect has to do with the way your brain recalls information. When you think about “action-thriller heroes,” you automatically land on the most prototypical, or common, examples you’ve seen (for example, Dwayne Johnson). But the more you consider the question, the more your responses diverge from the prototypical response. Thus, in a category in which the prototype is male-gendered, generating more responses will push you to think beyond the prototype and decrease the likelihood of male-gendered responses.

We tested this mechanism in a study of role models for children, a domain with both male and female prototypes. Across two studies, we recruited 672 parents of young children and asked them create an initial list of three role models for their child and then told them to extend the list with three additional names. As anticipated, the initial list generated by the parents of boys contained mostly male role models (for example, Tom Hanks), indicating that it is a male-gendered category. And another expected result was that when these parents extended the short list, the number of women rose by 46 percent, compared with the original—a significant increase. Conversely, the initial list generated by the parents of girls contained mostly female role models (for example, Michelle Obama), indicating that role models for girls represent a female-gendered category. Consistent with the prototype divergence mechanism, for parents of girls, the number of women listed in the extended short list decreased by 7 percent compared with the initial one—a small, but as predicted, decline.

In our final study, we investigated whether a longer short list not only leads to more female candidates being considered but also results in a higher selection of female candidates. We recruited 2,166 people with experience in the technology industry and asked them to complete the tasks regarding a start-up looking for a CEO used in our earlier experiment. In this study, we randomly assigned participants to generate a short list of six candidates (the longer list condition) or a short list of three candidates (the shorter list condition). Consistent with the previous studies, whereas the shorter list condition produced a women-to-men ratio of about 1:5, the longer list one resulted in a ratio of about 1:4—a significant 16 percent increase in the number of female candidates. When it came to selecting the preferred candidate, however, female candidate selection in the longer list condition (17 percent) was not significantly higher than in the shorter list condition (15 percent).

While it is disappointing that the consideration of more women did not lead to the selection of more women, this study illustrates the reality that the informal short list is just one of many steps in the professional advancement process. Research finds that different steps require different interventions to promote gender equity. An intervention that increases the odds of one making the short list may not increase the odds of one coming out on top. But we should not expect a single intervention to affect every step of the process. We should think of the longer short list intervention not as a silver bullet but as a building block that can work alongside other interventions toward gender equity goals. These might include explicit pushes to hire more women or campaigns that weaken the gender stereotypes associated with a role.

Our findings show that extending the informal short list can improve gender equity in the recruitment process, particularly for male-dominated roles. This strategy is immediately applicable to hiring managers but also to anyone in a position to allocate professional opportunities, such as mentorships, training, team assignments or third-party referrals. There are still limitations to keep in mind. For instance, our studies were survey experiments. The next step for future research is to replicate our findings in field or organizational settings. We hope that researchers and practitioners will continue to test the longer short list effect as a low-cost step toward furthering gender equity.