I carried out a survey of software engineers to establish if there was a significant difference in computer self-efficacy between genders. As expected women were less confident in their coding skills than men. However men over 30 did not show a greater confidence in their abilities than women in the same age group. I propose that this is related to the retention of women in the software industry. Less able women choose to leave the profession and more confident, better qualified women remain. My theory is based on research carried out into pull requests and gender in GitHub.