Natalie Bennett, Nick Clegg, Nigel Farage, Ed Miliband, Leanne Wood, Nicola Sturgeon and David Cameron take part in the ITV leaders’ debate. Photograph: ITV

One of the most striking images of the first televised UK general election leadership debate on Thursday, April 2, 2015, was the comparison of the seven party leaders on the platform including three women: Nicola Sturgeon (SNP), Natalie Bennett (Green), and  Leanne Wood (Plaid Cymru).

The flash opinion polls immediately after the debate asking the public who won were divided, with YouGov putting Nicola Sturgeon first, while the Guardian/ICM Unlimited survey reported that Miliband and Cameron were neck-and-neck.

One question arising is whether the sex of the leaders had any impact on how women and men evaluated the leaders’ performance?

Do women voters lean in towards women leaders?

The first graph shows the breakdown from the Guardian/ ICM Unlimited poll of whether the leaders were seen by women and men to have performed either ‘very well’ or ‘quite well’.  The gender gap can be calculated as the difference in women and men’s performance evaluations.

Thus compared with women, men favored the performance of two male leaders: Nigel Farange (by a substantial 9 points) and Nick Clegg (by 4 points). Greater support among men for UKIP was consistent with broader gender gaps in support for radical right-wing parties found throughout previous British and European research.

By contrast, women favored the performance of the three women leaders: Wood (by a substantial 11 points, the largest gender gap recorded in the survey), Bennett (by 9 points) and Sturgeon (by 5 points).

For the two major leaders – Ed Miliband and David Cameron – there was no significant gender gap in judgments about their performance.

Gender gaps in voting intentions?

But of course any gender gap could be produced by underlying patterns of party support rather than by the sex of the leaders per se, for example if women generally preferred the nationalist parties or those on the left of British politics.  A gender gap where women voters are more left-wing has been reported in many OECD countries in recent years, reflecting the pattern common in the United States since the early-1980s. To check this pattern, the second graph compares voting intentions for men and women in the same survey.

The results confirm that men are indeed more likely to express voting support for UKIP – producing a 5 point gender gap. But the gap was greater by UKIP leadership performance rather than voting intention.

By contrast, there is no significant gender gap reported for Plaid Cymru or the Scottish National Party, and only a small (2 point) gender gap where women are more inclined toward voting Green. The largest gender gap in voting intentions (4-points) is women’s greater support for the Labor Party, while no significant gender gap can be observed in judgments of Miliband’s performance.

Gender matters in leadership evaluations

Thus the comparison based on the Guardian/ICM Unlimited flash poll suggest that the gender gap in evaluations of leadership performance during the British election debate were influenced by the sex of the leaders; this gap was not simply the result of prior party preferences.

The performance of the women party leaders (Bennett, Wood and Sturgeon) connected more favorably with women voters,  and this was not simply the product of existing gender gaps in party support.  By contrast,  men greatly favored the performance of Farange, and the gender gap here was larger than in voting support for UKIP.

In short, in British politics today, the survey evidence indicates that sex matters for political leadership.  It probably does so by providing a cognitive short-cut – especially for judging less well-known leaders for minor parties where people are relatively unfamiliar with their background, experience or policies.

One possible implication for British politics is that if Labor had selected a woman party leader instead of Ed Miliband, they could possibly have capitalized and potentially expanded their modest 4-point lead among women voters. Since there are more women than men voters in the electorate, this could have made all the difference for party fortunes in the close contest. There may be some lessons here for future leadership choices in Britain. Whether there are similar implications for other countries, including the potential capacity of Hilary Rodham Clinton to reinforce women’s support for the Democratic party, remains to be determined.

Pippa Norris is Professor of Government and International Relations at the University of Sydney, the Maguire Lecturer in Comparative Politics at Harvard’s Kennedy School of Government, and Director of the Electoral Integrity Project.