Less than 50% of American men would be "very comfortable" with a female head of government, according to a survey published on Tuesday that found men in Britain and the United States growing less comfortable with women in positions of power.
The Reykjavik Index for Leadership, launched in 2018 by a group of female politicians to look at attitudes towards women leaders in industry, government and other roles, found they had grown more negative in both countries in the past year.
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In the United States, men's attitudes to female leaders in several areas of public life from politics to the judiciary grew more negative and just 49% of male respondents said they would be "very comfortable" with a woman as head of government.
In Britain, where a number of female lawmakers have dropped out of upcoming elections citing a rise in online trolling and other abuse, the number of male respondents who said men and women are equally suitable to lead fell.
Women's attitudes to female leaders, by contrast, remained consistently positive in both countries, creating a widening divide in opinion between genders, according to Kantar, the research company that conducted the survey of wealthy countries.
The growing gap could reflect "frustrations with former Prime Minister Theresa May and her Brexit dealings, and more polarised opinions in society more generally," said Michelle Harrison, global CEO of Kantar's Public Division.
"Similarly, in the U.S., the level of dissonance between the views of women and men has increased since 2018," she told the Thomson Reuters Foundation in an email.
"This may to an extent reflect a political and cultural shift in the USA, where high-profile women in politics, the media and entertainment and sport have seen increased misogyny directed towards them."
Researchers interviewed 22,000 people aged between 15 and 65 from July to September about how they felt about women leaders for the index.
The index was launched at the Women Leaders Global Forum, where hundreds of women political leaders gathered in Reykjavik in Iceland, the first country to make it illegal to pay men more than women.
The latest survey identified Canada and France as the countries with the most equal attitudes towards women and men in leadership, while attitudes in Japan, Germany and Italy had grown more positive in the 12 months since the first survey.
The United Nations has made women's equal participation in politics by 2030 one of its global development goals, and it says more women in leadership also drives economic growth.