I, We, or no one: Does gender matter?

How do writers refer to their own single author work when writing about it? Do they use singular pronouns (e.g. 'I predict the existence of a 9th planet'), more participative plural pronouns (e.g. 'Our model fits the observed data'), or avoid pronouns all together (e.g. 'The paper examines tool usage by parrots')? Is there a difference between male and female authors?

In a previous post I looked at 60,000 Economics publications over 30 years to check what do single authors actually choose to do. The data shows that authors of more recent publications tend to use the passive form less frequently, and that more experienced authors tend to use the singular pronouns more often.

Should gender matter for the choice of pronouns? Recent research into gender and preferences has shown that gender can have a strong effect on behavior and choices. Women tend to seek less competition, take less risk, and avoid over-confident behavior relatively to men. In our case, if using 'I' and 'My' is a sign of (over)confidence, it is possible that male authors would tend to use it more often. If there is a perceived risk in accentuating your own contribution by using 'I', then female authors might be more likely to use 'We' or a passive tone. In practice, the opposite occurs:

This graph above shows the fraction of authors using singular pronouns over time and by gender. Female single authors are consistently more likely to use 'I' and 'My', and less likely to use 'We' and 'Our', than male authors. This result is highly statistically significant, even when controlling for other factors such as experience, citations, and journal ranking.

All in all, female economists are about 20% more likely to use single pronouns than male authors. What can explain this large difference in choice due to gender? the floor is open for suggestions!