Parliamentary Women Opposition Leaders: A Comparative Assessment Across 28 OECD Countries

While women have increasingly gained access to the position of opposition leader, we still know very little about their pathways to that office. Therefore, this article seeks to uncover the dynamics and patterns that shape the ascendency of women politicians to the office of opposition leader from a comparative perspective. In this article, opposition leaders are understood as the parliamentary party group leaders of the largest non‐governing party in a given legislative assembly, which marks the closest equivalent to the Westminster understanding of leaders of the opposition that continues to dom‐ inate international notions of opposition leaders and oppositional leadership in parliamentary democracies. We draw on data from opposition leaders in 28 parliamentary democracies between 1996–2020 to identify opportunity structures that allow women opposition leaders to emerge across countries. In addition, we test how factors on the individual level (e.g., previous experience in party and parliament as well as in government) and at the party level (e.g., ideology) affect the likelihood that a parliamentary opposition leader is a woman. Our analyses demonstrate that the share of women in par‐ liament significantly increases the likelihood that at least one of the parliamentary opposition leaders of the past 25 years was a woman. Moreover, opposition leaders in leftist parties are more likely to be women than their more rightist coun‐ terparts. Surprisingly, and contrary to our expectations, previous political experience does not shape the probability of women becoming opposition leaders. Thus, overall, the institutional and ideological contexts of selecting parliamentary opposition leaders seem to matter more than the experience and qualifications of individual candidates.


Introduction
Over the past decades, women have (more or less) continuously gained access to political leadership positions. Not only in governments, and governing parties for that matter, but also in opposition parties have women increasingly made their way to the top. The available literature reflects, however, only just about half of that empirical picture. While there is a burgeoning literature on women presidents, prime ministers, and women cabinet ministers (Annesley et al., 2019;Curtin et al., 2022;Jalalzai, 2013;Krook & O'Brien, 2012;Martin & Borelli, 2016;Müller & Tömmel, 2022;Müller-Rommel & Vercesi, 2017), comparative research on women opposition leaders has, with very few exceptions (e.g., Clemens, 2006) remained conspicuously scant. This situation is genuinely astounding, not only because opposition research has turned into a major growth sector of comparative political studies (see, e.g., Helms, 2022a), but also because issues of opposition would seem to possess a natural affinity with some of the most fundamental concerns of feminist political research. To fill that striking gap, this article seeks to identify the factors that favour the emergence, or absence, of women opposition leaders across different democratic systems.
To begin, a conceptual note is in order: As the editorial piece to this thematic issue sketches out (see Dingler et al., 2023), there is a wide array of possible notions of opposition leaders, none of which can reasonably claim to be equally valid for all contexts. In this article, we define opposition leaders in the traditional Westminster sense where applicable, or as the parliamentary party group leaders of the largest non-governing party in a given legislative assembly. The latter notion is closely linked to the Westminster understanding of opposition leaders-marked by the combination of holding the party leadership of the largest non-governing party in parliament, and operating from the centre of parliament-which has strongly shaped international notions of opposition leaders and oppositional leadership in parliamentary democracies well beyond the world of Westminster. That said, there are several differences between leaders of the opposition in Westminster systems and their closest equivalents in other types of parliamentary regime. Most importantly, parliamentary opposition leaders, as defined above, can be but do not have to be their party's leader; the defining institutional feature is being the leader of the parliamentary party group. In many parliamentary democracies from beyond the Westminster family, the offices and roles of party leader and parliamentary party leader can be split up between two different politicians. Actually, either of the two positions can be divided between two persons, and indeed, dual leadership arrangements have become popular features of party politics across different regimes (Campus et al., 2021). One apparent major difference concerns the selection and selectorates of opposition leaders in Westminster-type and other types of parliamentary democracy. However, while it could be expected that the nature of leadership selection in parties and parliamentary party groups differ categorically, the differences actually tend to be moderate in constitutional practice. Indeed, in their major study of four Anglo-parliamentary democracies, Cross and Blais (2012) highlighted the conspicuously prominent role of the parliamentary party in party leadership elections, and in terms of intra-party power more generally. That is, while being party leaders rather than parliamentary party group leaders in name, party and opposition leaders in Westminster systems tend to be very much creatures of parliamentary party politics, thereby strongly resembling parliamentary party group leaders as opposition leaders as to be found in many parliamentary democracies beyond Westminster.
That said, there are other differences between Westminster and other types of parliamentary democracy. While leaders of the opposition at Westminster are the natural candidates for the premiership, this applies to a considerably lesser extent in many other parliamentary systems. Wholesale alternations in government tend to be rare outside the world of Westminster, and even in the event of a change of government opposition leaders can well find themselves and their party as a junior partner, rather than the dominant party, in a complex coalition government. This alters both the status and the task description of opposition leaders. Depending on the structure of the party system, occasionally even the leaders of truly major opposition parties may be figures with little to no chance to become a leading protagonist in the political executive-even when the composition of the government changes. This is true especially for many parties and parliamentary party leaders from so-called "pariah parties" (Moffitt, 2022) or "new challenger parties" (De Giorgi et al., 2021). In these cases, the office and role of opposition leader is much more that of a "chief attacker,'' rather than that of a "head of government in waiting," which may require fundamentally different qualities. Obviously, even in Westminster contexts, some leaders of the opposition can be unlikely future prime ministers. After devastating electoral defeats, and a party's recent fall from power after an extended term in office, leaders of the opposition cannot realistically hope to win the premiership anytime soon. Key tasks of the leader may then, at least temporarily, focus mainly on healing intra-party rifts and organizing intra-party reforms, rather than getting ready to govern the country.
For all those ambivalent features, the office and role of leader of the opposition in the parliamentary arena is invariably important across different parliamentary democracies. After all, the very idea of parliamentary government centres on the distinction between government and opposition. In the age of dramatically advanced levels of personalization of politics, this central element of parliamentary democracy has become increasingly personalized and leader-centred. In any case, it seems reasonable to assume that being an opposition leader is not just a unique and distinctive role, but also one gendered in unique and distinctive ways.
Given the striking lack of previous research on those issues, this article can only make the first steps towards understanding the politics of women opposition leaders. This journey has to begin with establishing under what circumstances women leaders of the opposition emerge, and where they have remained absent despite the growing alert to gender issues that have come to mark most parts of the democratic world.
Looking into 28 parliamentary democracies between 1996 and 2020, we, first, posit that the share of women in national legislatures affects the probability that at least one of the opposition leaders of the past 25 years was a woman. The larger the share of women MPs, the greater the pool of qualified candidates, and the lower the social barriers that women are likely to face on their way to leadership positions within their parliamentary party (Escobar-Lemmon & Taylor-Robinson, 2009;Jalalzai, 2008). Second, we expect that opposition leaders in leftist parties are more likely to be women than their rightist counterparts since they have more effective mechanisms in place to promote women, and higher incentives for a more balanced leadership structure that meets the expectations and demands of their supporters (e.g., Davis, 1997;Kittilson, 2011;Krook, 2009). Third, in line with key findings from the recruitment literature, we propose that women opposition leaders are likely to be more experienced and to hold higher qualifications than their male counterparts (e.g., Beckwith, 2015;Kroeber & Hüffelmann, 2021;Müller-Rommel & Vercesi, 2017) in order to keep widespread stereotypical reservations at bay and overcome the various obstacles they face. Based on unique data from 204 opposition leaders in 28 parliamentary democracies between 1996 and 2020, our analyses demonstrate that higher shares of women MPs do indeed provide favourable opportunity structures for women across countries. Moreover, the odds that an opposition leader is a woman tends to be higher in leftist than in rightist parties. Interestingly, however, the actual requirements for women opposition leaders do not seem to differ much from those of men. The findings from our inquiry-which marks the largest comparative study on women opposition leaders, and opposition leaders of whatever gender for that matter, yetsuggest that, for the career paths of senior opposition politicians, the respective nature of the parties is more important than the individual political experience of candidates. With these findings, we add to the quickly growing literature on women in political leadership positions by adding another nuance about the much-overlooked role of opposition leader. Overall, our results provide a reason for some optimism regarding the realization of more diverse forms of democratic government, since women opposition politicians do not seem to be held to higher standards-or at least not as far as the selection process is concerned. That said, even in the established representative democracies-where women have made major inroads in legislative and executive politics-biases against women do remain embedded in political parties.
In the next section, we provide a more detailed explanation of our guiding assumptions. This will then be followed by an empirical analysis of patterns of recruitment of 204 opposition leaders. The conclusion puts our findings in a broader context, highlights the implications of those findings, and identifies avenues for future research in that field.

Women Opposition Leaders: Opportunity Structures, Parties, and Candidates' Experience
Notwithstanding the major advances of the past, most political leadership positions remain men-dominated. There are still comparatively few women presidents, prime ministers, cabinet members, or party leaders across countries and political regimes. Research on political career paths and recruitment suggests that differences in opportunity structures across countries shape the possibility of women rising to top positions. In coun-tries with favourable opportunity structures, party-as well as individual-level factors are crucial in determining who makes it to the top. In this article, we argue that similar conditions and patterns apply to women opposition leaders and that the share of women in parliament strongly shapes women's chances to become opposition leaders. Furthermore, in countries that have experienced the emergence of women opposition leaders, we expect party ideology as well as previous political experience to have been key factors shaping the likelihood that women, compared to men, become parliamentary party group leaders of the largest non-governing party in a given legislative assembly.

Rising to the Top: Opportunity Structures
In order to understand under which circumstances women are selected as opposition leaders, it is important to take into consideration political opportunity structures at the country level. One crucial factor shaping the likelihood of whether a woman becomes opposition leader is the share of women MPs in a given legislature. Since the typical career path of most opposition leaders includes longstanding experience as an MP, higher percentages of women in legislatures (with some women MPs being reelected to parliament) should gradually lead to a larger pool of reasonably experienced women candidates (Escobar-Lemmon & Taylor-Robinson, 2009), who can successfully compete for the position of parliamentary party group leader.
In addition, the share of women in a legislature is a predictor for the exposure to women politicians. A more diverse legislature in terms of gender distribution also signifies a "general openness of a political system to women's participation" (Jalalzai, 2008, p. 213) that should translate into fewer barriers for women to advance to political leadership positions. Under these circumstances, women should face less prejudice concerning their ability to lead a parliamentary party group, since women in electoral office accustom their party colleagues to the idea of women as political leaders (Alexander, 2015;Alexander & Jalalzai, 2020). Some scholars argued that there might be a "critical mass" phenomenon at work (see Dahlerup, 1988); i.e., (only) from a certain number or share, the representation of women in parliament tends to make a real difference in terms of public policies as well as for legislatures as a workplace (see O'Brien & Piscopo, 2019). However, it has remained contested as to what share of women MPs actually marks that critical threshold, if it exists at all (see, e.g., Childs & Krook, 2008). This notwithstanding, empirical studies on the selection of party leaders and cabinet ministers provide ample evidence that in democracies with more gender-equal legislatures women are more likely to raise to different types of leadership positions (Escobar-Lemmon & Taylor-Robinson, 2005;Goddard, 2019a;Reynolds, 1999;Verge & Astudillo, 2019). Following this line of argument, we expect to find that a higher share of women legislators provides better opportunities for women to become parliamentary party group leaders of the largest opposition party: H1: The higher the share of women MPs in a legislature, the more likely a woman is to become opposition leader.

Rising to the Top: Party-Level Factors
While favourable contexts at the national level can provide opportunity structures for women, party politics is a crucial-in parliamentary democracies arguably the single most important-factor shaping political careers. Parties are powerful gatekeepers to leadership positions in government. This is true not just for both male and female career politicians (see, e.g., Dowding & Dumont, 2008); at least in parliamentary democracies, it is the parties that make and break the careers even of non-partisan "technocrats" as well (see Helms, 2022b). The literature on recruitment and gender also emphasizes the importance of intra-party dynamics for the career advancement of women. Women's successful political careers are shaped by favourable conditions within their party, for example, during crises (e.g., Beckwith, 2015), when the position seems to be particularly unattractive (O'Brien, 2015). In a similar vein, party ideology is a crucial determinant of women's representation, with left parties being more responsive to group representation demands and more "women-friendly" than rightist parties (Caul, 2001;Norris & Lovenduski, 1995;Paxton & Kunovich, 2003). Intra-party mechanisms that can enhance women's access to positions of power, such as parliamentary quotas or women's networks, typically tend to exist in left-wing rather than in more rightist parties (Davis, 1997;Kittilson, 2011;Krook, 2009). These mechanisms, in turn, should increase the supply of women able and willing to advance to influential positions within their respective parties. In addition to the supply of women candidates, the ideological orientation of the parties should also shape the demand for women leaders. Parties should be interested in being responsive to their voters' attitudes, e.g., with regard to their issue attention or responsiveness to voters' policy priorities (Klüver & Sagarzazu, 2016;Klüver & Spoon, 2016). Since voters of leftist parties tend to have more progressive gender attitudes, matters of gender equality should be salient for them and they should thus also have a higher incentive to see a woman being selected as the parliamentary party group leader and possible opposition leader.
Most of the literature supposes that rightist parties are reluctant to select women for leadership positions and that leftist parties appoint more women ministers (Claveria, 2014;Goddard, 2019b;Reynolds, 1999). Thus, we argue that both the demand for women parliamentary party group leaders and the supply of qualified women candidates to fill this post is higher in leftist parties: H2: Opposition leaders are more likely to be women in leftist than in rightist parties.

Rising to the Top: Individual Level Factors
Political resources such as political experience, party office-holding, and connections to political insiders are very likely to increase a candidate's chances of becoming a parliamentary party group leader. Typically, both women and men leaders have longstanding seniority in public or party offices. Yet, men and women might still benefit differently from political resources. Men tend to profit from homosocial capital like trust, "in-group" networking, and linkage to party selectors. High-trust networks remain closed to women since they usually form during exclusive social activities and events to which women often do not have access (Annesley et al., 2019, p. 29;Annesley & Gains, 2010;Franceschet & Piscopo, 2013). Given that parliamentary party group leaders need to enjoy high levels of trust, the absence from these inner circles is likely to generate doubts concerning women's trustworthiness and loyalty. It can thus be plausibly argued that women have to be exceptional and better qualified than their male counterparts to compensate for the lack of male homosocial capital. Recent research on ministerial career paths in 28 European countries demonstrates that career paths continue to be gendered, with men rising to influential ministerial positions (e.g., resourceful portfolios) with a lot less experience than women (Kroeber & Hüffelmann, 2021). In addition, gender and political recruitment studies argue that the career profiles of women ministers and prime ministers are different and often exceptional; they specifically tend to be marked by higher levels of experience in other political offices compared to their male colleagues (e.g., Jalalzai, 2013;Müller-Rommel & Vercesi, 2017;Verge & Astudillo, 2019). In addition to that, even if the overall number of women as party leaders increases, they tend to meet higher demands (O'Brien, 2015), and once in office need to perform better in elections than their male colleagues in order to survive . Beyond the level of party leaders and executives, such as when running for legislative office, evidence suggests that women tend to be better qualified than men (for an overview see Bauer, 2020). Based on these considerations, we expect that women have more political experience in parliament, at the party level, and as government ministers than men in becoming opposition leaders: H3: Women are more experienced and better qualified than men on becoming opposition leaders.

Empirical Strategy
To test these propositions, we follow a two-stage strategy. In a first step, we examine opportunity structures of women to become opposition leaders across countries.
In the second step, we investigate which factors explain the presence of women opposition leaders in countries that have had at least one woman opposition leader between 1996 and 2020. To this end, we collected biographical data on 204 opposition leaders in 28 OECD countries. The focus on OECD countries allows studying democracies that outperformed other world regions concerning women's representation in top positions. In addition, all these countries are established parliamentary democracies in which the role of opposition leader is normatively acknowledged and usually important in both constitutional theory and practice, even in the absence of British-style adversary politics. Our choice of countries is characterized by a broad variation in the key variables of interest, while institutional and socioeconomic contexts across the countries covered remain comparable. Thus, they provide ideal testing grounds for a large-scale comparison and possess broad generalization potential.

Dependent Variable
In line with our conceptualization of opposition leader, we include parliamentary party group leaders and, in Westminster systems the party leaders of the biggest non-governing party in parliament (who effectively lead their parties in the parliamentary process). This means that, for each country, we only have one observation at any given point in time (except if two individuals share the leadership position). Further, we only included opposition leaders that were in office for at least six months, since we expect the selection of interim party group leaders to follow its own logic. Based on this definition, we identified 204 opposition leaders in 28 OECD countries who were in office on 1 January 2000 or later (for a list of countries included see Supplementary File, Table A1). Since some of these opposition leaders took office before January 2000, their length of time in office determines the time span covered (1996-2020) in our analysis. For the first part of the analysis, our binary dependent variable captures whether a country has had a woman opposition leader (1) or not (0) during the 25 years under investigation. In the second stage, our dependent variable is the sex of the opposition leader in countries with at least one woman opposition leader during the investigation period, which takes the value 1 if the leader is a woman. We include all opposition leaders in these countries between 1996 and 2020; the sample incorporates 94 (74.60%) men and 32 (25.50%) women from 16 countries. This, in turn, means that in 12 out of our 28 countries no woman held the position of opposition leader. To ensure that this approach does not yield a selection bias, we ran a two-step Heckman correction model. As reported in the Supplementary File (Table A7), this alternative strategy does not alter our results, and since the lambda term does not reach levels of conventional levels of significance, we are confident that we do not face a selection bias.

Explanatory Factors
To test H1, the analysis comprises one explanatory variable: the mean share of women MPs in a country between 1996 and 2020 (as provided by Inter-Parliamentary Union, 2022). Furthermore, to test H2, we include the ideology of parties based on the Manifesto Project Database (Volkens et al., 2021) in the year of the start of the opposition role. If data for the exact same year when a candidate assumed office was not available, we used the closest year before the selection of the opposition leader. Finally, we include several variables that measure the political experience of the opposition leader: previous role as parliamentary party group leader (1 = yes), previous experience as government minister (1 = yes), party leadership experience (1 = yes), and time in office as MP in years (+1, lagged). All this information was retrieved from websites of parliaments and politicians or newspapers and measured at the time when a candidate took office in order to account for previous experience.

Control Variables
Beyond these explanatory variables, we control for numerous other factors that have been identified by previous research as affecting men's and women's career paths in politics. In the first part of the analysis investigating opportunity structures, we include the mean of women's labour force participation based on data from World Bank (2022a), as labour force participation is an established proxy for the status of women in a society, which can affect the likelihood of women to become leaders. We also account for the term length of a legislative term based on ParlGov (Döring et al., 2022), as shorter terms go hand in hand with higher turnover rates and thus might provide a more positive opportunity structure for women.
In the second step of the analysis, when tracing the effect of ideology and previous experience, we also account for several factors at the individual and party level. First, we include the age of the opposition leaders at the start of their tenure (based on our data). Second, we include a variable measuring the positions of gender equality of a respective party from the Manifesto Project Database (Volkens et al., 2021), as previous research has shown that more gender-equal parties are also more determined to promote women. Third, since women tend to be selected to party leadership positions in contexts of poor party popularity (Wiliarty, 2008), we include a measure designed to capture whether a party has lost seats in the election right before or at the time of the opposition leader's start in office based on ParlGov (Döring et al., 2022). We also include change in GDP growth to measure whether a country faces economic challenges (World Bank, 2022b). Fourth, we include variables measuring whether a party or country quota exists (based on Inter-Parliamentary Union, 2022). Finally, we also include country-fixed effects to model variation at the country level.

Analysis
At the first stage of the analysis, we inquire which factors positively shape opportunity structures allowing women opposition leaders to emerge across countries in order to test H1. In the second step, we analyze which party and individual-level factors enhance the likelihood that a woman becomes opposition leader.

Factors Providing Favorable Opportunity Structures
During this first stage of the analysis, we aim to shed light on the opportunity structures that allow women to become opposition leaders. In detail, we investigate the difference in the likelihood of a country having a woman opposition leader in order to test H1, which proposes that a higher share of women MPs marks a more favourable opportunity structure for women candidates. Table 1 and Figure 1 display a logistic regression model of country-level factors indicating the likelihood that at least one opposition leader was a woman. All coefficients display odds ratios. In line with our hypothesis, a higher share of women leads to higher odds that the country has witnessed a woman opposition leader. This effect reaches conventional levels of statistical significance (p < 0.10). For example, in a country with a mean share of 24% women MPs, such as Luxembourg, the probability that within the last 25 years one opposition leader was a woman is around 50%. By contrast, in a country with around 45% of women in parliament like Sweden, the likelihood that at least one of the opposition leaders was a woman reaches about 90% ( Figure 1 displays these findings visually). It also demonstrates that we cannot make any predictions about the opportunity structure for contexts with very low numbers of women MPs, since in these contexts the effect is not statistically different from 0. Moreover, as Table A5 from the Supplementary File demonstrates, we cannot trace a critical mass of women MPs (e.g., 15% or 30%) needed to provide favourable opportunity structures for women seeking to advance to the top of the largest opposition party. The influence of women MPs hence seems to be more fluid than suggested by the advocates of the critical mass theory. Generally, these findings echo previous  research on executives and party leaders contending that the share of women positively affects the pool of suitable candidates, and exposure to women political actors reduces barriers for them to become political leaders (Escobar-Lemmon & Taylor-Robinson, 2005;Goddard, 2019b;Reynolds, 1999;Verge & Astudillo, 2019). Turning to the control variables, neither women's labour force participation nor the length of the legislative term significantly affect the structural opportunities for women candidates and thus the likelihood of a country to have witnessed a woman opposition leader in the past quarter of a century.

Party Identification and Political Experience of Opposition Leaders
In this second step, we reduce our sample to countries in which at least one opposition leader since 1996 was a woman in order to make predictions about the party and individual-level factors that shape women's and men's chances to become the parliamentary party group leader of the largest opposition party. Thus, we now work with 130 observations (i.e., Table 2 and Figure 2 provide the results of a logistic regression of party-and individuallevel factors on the likelihood that the opposition leader is a woman).
In line with H2, the chances for women to become opposition leader decrease with a more rightist ideology of the party (with higher values of the right-left index signifying more rightist positions). This effect reaches conventional levels of statistical significance (p < 0.01). Even if we use different operationalization strategies to measure left-right ideology (e.g., a dichotomously variable instead of a continuous measure), these findings remain robust (see Supplementary File, Table A6). Figure 2 displays this effect visually. Interestingly, the effect vanishes  for parties at the very right of the political spectrum. It could be plausibly contended that some rightist parties employ women leaders in a strategic attempt to soften their profile and increase their appeal for less radical sections of possible supporters, but we cannot make any empirically proven statements about the likelihood that parliamentary party group leaders of these parties are women, or why. The overall findings are, however, clearly in line with previous research on party leaders and executives, which shows that leftist parties are more likely to select women for high leadership positions (Claveria, 2014;Goddard, 2019b;Reynolds, 1999). Finally, looking at individual-level factors in Table 2, we see that-importantly-none of the variables measuring experience before becoming opposition leader has an effect on the chances of women winning that office compared to men. As Tables A4 through A7 in the Supplementary File show, men and women opposition leaders do not have significantly different career paths and even once we include different measurements of the variables, such as years in a government position or as parliamentary party group leader, these results do not change. Thus, we have to reject H3, which predicted that women are held to higher standards in the selection process than men and that women opposition leaders need more experience to be considered eligible. Our results hence challenge findings from recent research on candidates running for chief executive positions at the national or regional level (e.g., Verge & Astudillo, 2019). One reason for this might be that we only measure men and women who succeeded in becoming opposition leaders; yet, with our data, we cannot make any predictions about whether contenders for this position had similar qualifications or not.
Turning to our control variables, we observe that neither age nor seat losses of a party, and neither the existence of a dual leadership structure or quotas have any significant effect on the likelihood of the opposition leader being a woman. The only control variable that has a significant effect is a variable measuring parties' stance on equality matters. In line with prominent theoretical expectations, the more equality-oriented a party is, the more likely is the opposition leader to be a woman. The results of additional models including factors that might also affect the likelihood that the opposition leader is a woman are reported in Table A5 in the Supplementary File. Controlling for contextual factors that might shape incentives of leading opposition parties (e.g., GDP growth, unemployment rates, the gender of the head of government) does not substantively alter our findings.
Overall, our two-step analysis demonstrates that favourable opportunity structures provided by higher seat shares of women in legislatures allow women to become opposition leaders. Those men and women that make it to the top are not as different as previous research led us to expect; by contrast, they have similar levels of experience in relevant leadership positions. However, with regard to ideology, opposition leaders are more likely to be women in more leftist parties. It remains to be studied if and how women's leadership performance in opposition parties differs from that of men. What we know is that, on average, the tenures of women leaders of the opposition were about 2.5 months shorter than those of their male counterparts in the countries concerned. Some women-most prominently Margaret Thatcher and Angela Merkel-became longstanding and powerful heads of government, while many others had considerably less successful trajectories. In any case, it is important to note that the length of tenure as opposition leader (measured as time in office) allows for fundamentally different interpretations. Specifically, unlike a short-term premiership, a notably short stint as leader of the opposition does not necessarily signal weakness, under-performance, and/or a loss of power-it may equally well indicate just the contrary. For example, New Zealand's Jacinda Ardern advanced to the premiership in 2017 after less than three months as leader of the opposition to become the country's most popular prime minister in a century.

Conclusion
This study marks, to our knowledge, the largest comparative study on women opposition leaders as yet, and parliamentary opposition leaders more generally, covering 28 OECD parliamentary democracies over nearly three decades. Based on the conceptualization of opposition leader as the parliamentary party group leader of the largest non-governing party, our findings reveal that in countries with more gender-equal parliaments, the probability that a woman reaches this leadership position raises. It seems that only if a sufficient pool of qualified candidates exists and social barriers are reduced through exposure to women's political actors, women stand a reasonable chance to become opposition leaders. The debate about when, exactly, the pool of women is sufficiently large and when (institutional) practices indeed become more open to the successful ascendency of female candidates to leadership positions remains unsettled (Bratton, 2005;Childs & Krook, 2008;Dahlerup, 1988). Furthermore, in countries where women have made it to the top, leftist parties, when being the largest non-governing party in parliament, are more likely to have a woman as parliamentary party group leader than rightist parties under the same conditions. Probably, their commitment to gender equality and the respective measures in place, combined with the demand of their voters, positively affect their willingness to select a woman for this post. Interestingly, and contrary to what much of the literature on recruitment suggests (e.g., Jalalzai, 2013;Müller-Rommel & Vercesi, 2017;Verge & Astudillo, 2019), the chances that an opposition leader is a woman are not shaped by previous experience. Thus, apparently, women do not seem to be held to higher standards, or at the least not concerning the selection process for leadership positions in opposition. Overall, party ideology thus seems to be more important than personal experience for women on their possible rise to the position of opposition leader. With these findings, this article not only breaks new ground by focusing specifically on leaders of the opposition; it also contributes at least indirectly to the burgeoning literature on women presidents and prime ministers, woman cabinet ministers, as well as leading woman executives at the supranational and international lev-els (Annesley et al., 2019;Curtin et al., 2022;Haack, 2022;Jalalzai, 2013;Krook & O'Brien, 2012;Martin & Borelli, 2016;Müller & Tömmel, 2022;Müller-Rommel & Vercesi, 2017)-simply because many, if obviously by no means all (Helms, 2020), top executive careers in politics start in opposition. That said, we have to keep in mind that our analyses only cover successful candidates, i.e., those who have made it to the top. Future research may want to consider also those candidates that presented their candidacy for the position of parliamentary party group leader but eventually failed to be elected, in order to shed light on how women fare compared to their direct competitors.
Further, that leftist parties in opposition are more likely than centre-right parties to be led by women, while many women prime ministers in Europe have come from centre-right (see Müller-Rommel & Vercesi, 2017) or right-wing parties (Beckwith, 2022), points to the complexity of political careers and power structures in many representative democracies. This begs for more research on gendered careers specifically applying a government and opposition perspective. Another key question that could and should be addressed by future research concerns the idea that men and women opposition leaders might perform-and be perceived-differently once in office. Existing literature leads us to expect that women face additional obstacles even after having gained political office (e.g., O'Brien et al., 2015). It would be fascinating, and important, to uncover patterns of longevity, electoral, and political performance of women opposition leaders compared to men. Addressing these issues in a systematic way would allow us to understand how and to what extent women can influence political outcomes in their role as opposition leaders, and whether they face additional challenges and barriers when it comes to keeping that office.
Beyond the selection and performance of opposition leaders, future research should investigate the consequences of women's access to opposition leadership for the wider cause of women's representation. More research is needed to determine whether women in these critical positions are more likely, for example, to select women as influential committee chairs or for other prestigious positions. Finally, future studies could shed light on the link between women opposition leaders and the substantive and symbolic representation of women. Indeed, women opposition leaders would appear to have the potential to serve as "critical actors" whose influence may be crucially important to women's policy representation and political empowerment, and the quality of democratic governance more generally.
Ludger Helms is professor of political science and chair of comparative politics at the University of Innsbruck. His research focuses on comparative political institutions, executive politics, political oppositions, and elites. He is the author of some 150 scholarly publications in those fields.