Issues in Interdisciplinarity 2018-19/Evidence in the Gender Pay Gap
This chapter investigates the use of evidence within the Gender Pay Gap, both from a historical perspective, so as to establish this as an ongoing predicament, and from disciplinary lenses, highlighting current differences of opinion.
The Gender Pay Gap is a "measure of the difference between men’s and women’s average earnings". It is commonly accepted that this disparity is not necessarily born from unequal pay for equal work but instead from a historically persisting custom of women's working restrictions, upholding cultural values, and labour division, with male careers often commanding higher wages.
In 1906, twelve countries committed to a treaty as part of a string of new laws dramatically limiting women's nighttime working-hours. To justify these laws courts often referred to "empirical evidence", originating from practical data collected from factory inspectors' reports and the observations of "medical men", showing that night work cause negative physiological effects in women including loss of appetite, increasing morbidity and mortality. Although the courts valued their evidence, we could question its validity based on whom it was collected by and how few people had access to this data.
In 1932, the BBC introduced a marriage bar (the practice of terminating women's employment upon marriage or pregnancy, or not hiring married women). Such restrictions were widespread during the interwar-years, and were even pursued in the public sector (within teaching, civil service and medicine). It was argued that the bar was necessary in response to the economic depression and high male unemployment. However, many felt that the economic rationale cited as evidence for the need of the bar was simply the publicly-presented evidence, and not the true reason why it was put into place. Commentators believed that a social consensus on women's participation in public life was instead to blame. Here, we are faced with how evidence might be selected and manipulated to support one's own rationale.
These are just two of many historical examples of the ongoing issues related to evidence within the restriction of women's work.
Over time, the ways we collect and use evidence have dramatically evolved. This has allowed disciplines already addressing the issue (such as Economics) to delve further into the situation, as well as allowing a plethora of disciplines to approach the issue (such as Sociology and Psychology).
Current disciplinary perspectives
Economics uses quantitative evidence concerning disparities in wages and working hours between sexes to explain the gender pay gap. Their main focus is decomposing this evidence into particular gendered categories concerning age, field of study, level of education, interests and balance between home and work. By doing so, the proportion of this pay gap caused by gender discrimination decreases.
Indeed economists consider that data generalisations and lack of analysis of all relevant variables have caused the contradictions surrounding this gap.  For instance, its political/social discourse mostly uses imprecise evidence such as: “women’s wages”, whilst economic studies focus on highly specific data like “Hours distributions and hourly wage penalties and advantages for hourly workers across six occupational groupings, by sex”.
The decomposed evidence used, such as studies of trends in variables and convergence analysis, have concluded that a majority of this pay gap can be explained by the difference in choices men and women make. For instance, economists (such as Harvard professor Claudia Goldin) support the use of Becker’s human capital theory to explain why women orient themselves towards the jobs they do.
Sociology focuses on the reasons underpinning the degree of occupational sex segregation and why the sexual division of labour is significant in the difference in remuneration for both sexes. Whilst sociologists recognise that Becker's human capital theory plays a certain role in gender wage disparity, they argue that it in reality it only accounts for a fraction of the rift.  Rather than focusing on the autonomic "supply" side decisions, sociologists highlight broader cultural and infrastructural mechanisms as key contributors to the issue.
To explain sexual division of labour, sociology focuses on gender socialization as a cause of sex segregation. Their evidence for this are sociological studies displaying a positive correlation between a society's emphasis on gender differences and the extent of sex segregation. On a structural level, sociologists such as Reskin highlight personnel practices actively discouraging the mobility of sexes between certain occupations, particularly in the form of work-time schedules and work equipment.
Sociology suggests sexual division of labour in the workforce is paramount as female dominated spheres of work earn less on average - not because they are able to offer less in terms of human capital but because typically female work is systematically and culturally undervalued.  As a result, policies that ban direct discrimination fail to address the broader issue.
Psychology focuses on the sundry and specific behaviour of individuals, unlike sociological theory. They are interested in the wage-related impacts of confidence and individual’s personality as related to the skills of risk-taking, negotiation and competitive behaviours.
Psychology uses evidence collected from psychometric instruments, including achievement motivation and personality trait scales, capturing confidence. This approach largely ignores the wider social forces that may explain the gender pay gap.
Over-confidence is also statistically modelled so as to produce quantitative evidence for the variables giving rise to pay differences. An example of this would be the Oaxaca-Blinder decomposition model that suggests we can investigate dissimilarities in gender characteristics to explain differences in their remuneration for said characteristics.
We could argue that it was the lack of access to and manipulation of evidence that allowed for women's working restrictions to be sanctioned. Nowadays, however, we appear to be facing a different problem. Despite an abundance of accessible evidence, researchers today primarily interpret evidence from their own disciplinary perspective, often leading to a clash of opinions as explored above.
Economics often disregards qualitative or theoretical evidence, favouring quantitative empirical evidence. Whilst sociology values quantitative evidence, it recognises that it cannot sufficiently reflect the socio-cultural forces at hand and as a result gives equal precedence to qualitative evidence.   Furthermore, evidence used in psychology is individualistic, unlike the societal models of sociology, resulting in diverging conclusions regarding the pay gap.
Clearly, single-disciplined researchers tend to collect evidence from their own disciplinary perspective to inform their conclusions, lacking an understanding of that of other disciplines. Therefore, we believe in the need for interdisciplinary thinkers to overcome the lack of cohesion within the disciplinary perspectives. Due to their interdisciplinary foundations, an interdisciplinary researcher would have the capacity to approach and understand the theories provided by different disciplines without the ulterior motive to proliferate their own discipline's agenda. We feel an interdisciplinary approach would allow for a holistic interpretation of the breadth and depth of the evidence now available to us, hence reaching a more universal consensus.
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