Sarah,
This is the million dollar question. We are investigating additional factors that may increase or decrease confidence and likelihood to intervene. For example, our preliminary data indicate that seeing a role model intervene (as seen in a vignette) increases women’s confidence as compared to when a person in a vignette simply does nothing. The context in which someone views things also makes a difference – women in general show less confidence when exposed to more sexism (again in vignettes). These give us places to think about prevention work – having people model appropriate interventions should help and decreasing sexism in situations should also help. And that’s just two tiny pieces of the puzzle.