- Structural issues such as the long training period, the predominance of insecure posts at early career level and that the period when people establish themselves as independent scientists coincides with the period of family formation.
- Pragmatic issues: availability of affordable, high-quality childcare, difficulty of finding a job in the same geographic region as a partner, problems with travelling to attend conferences.
- Cultural: stereo-typing, unconscious bias, family expectations.
Not only are these factors inextricably linked but individually small disadvantages accumulate leading to lower overall success rates for women. The combination of circumstances that lead individual women to leave science will be unique for each woman. This means that attempts to isolate a single cause for the scarcity of women in science, for example, bias in appointments procedures, are unlikely to be successful.
It is apparent that the situation is different in different sciences. Very few women do physics, engineering and computer science in the first place (for UK figures see the UKRC Statistics Guide 2010) whereas in the UK over half of people attaining a postgraduate qualification by research in biological science are women (HESA, Table 7, Qualifications obtained by level, gender and subject area). It seems likely that the low numbers of women physics, engineering and computer science are predominantly due to cultural factors operating within schools. However, the example of the biological sciences shows that recruiting at the student level while clearly a necessary condition for increasing the number of women is not a sufficient condition. Structural and pragmatic issues must also be addressed if women are to be retained in STEM.