Universities have been urged to reconsider the use of large introductory courses in science degrees after research showed that they made female students much less likely to participate.

A study in , which analysed data from four US universities and two overseas, found that an increase in class size from 50 to 150 students decreased the likelihood of a woman participating relative to a man by 50 per cent.

The researchers, led by Cissy Ballen, assistant professor in the biological sciences at Alabama¡¯s Auburn University, looked at 44 science, technology, engineering and mathematics courses over two years, giving them 5,300 student-teacher interactions to analyse.

An increase in class size was found to have the most significant impact on female participation, with a negative effect starting to be detected when a lecture involved more than approximately 120 students.

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The data show that the largest gender disparities in participation occurred when academics?sought voluntary responses from students after asking a question in a large lecture hall.

Although the research did not look explicitly at why this might happen, Dr Ballen cited previous research?that found that women took time to ¡°work up the nerve¡± to answer questions, expressing concern about their ability and what other people might think. In contrast, men tended to have inflated perceptions of their ability, she said.

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The study followed previous research by Dr Ballen and others?that showed?that : as class size increased, women underperformed in exams and in the course overall compared with men.

Dr Ballen told Times Higher Education that the research showed that universities and their administrators needed to ¡°grapple with the data that show the harmful impact of large classes on student participation¡±.

In particular, they needed to halt the ¡°continued expansion of large, introductory gateway courses in science in US universities¡±, she said.

Dr Ballen said that the research also showed that lecturers could still have a positive impact even in large classrooms by using diverse and more equitable teaching strategies, as the research showed that women were more likely to participate after small-group discussions.

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This would be particularly useful as participation in higher education looks set to increase but institutions face constrictions to cater for increased numbers without increasing class sizes, she said.

Studies have shown that interactive classes are beneficial to learning and are increasingly commonplace in STEM courses, Dr Ballen said.

anna.mckie@timeshighereducation.com