leads to big losses for the economy. Causes for wage discrimination The non-adjusted gender pay gap (the difference without taking into account differences in working hours, occupations, education and work experience) is not itself a measure of discrimination. Rather, it combines differences in the average pay of women and men to serve as a barometer of comparison. Differences in pay are caused by: occupational segregation (with more men in higher paid industries and women in lower paid industries), vertical segregation (fewer women in senior, and hence better paying positions), ineffective equal pay legislation, women's overall paid working hours, and barriers to entry into the labor market (such as education level and single parenting rate). Some variables that help explain the non-adjusted gender pay gap include economic activity, working time, and job tenure. Gender-specific factors, including gender differences in qualifications and discrimination, overall wage structure, and the differences in remuneration across industry sectors all influence the gender pay gap. Eurostat estimated in 2016 that after allowing for average characteristics of men and women, women still earn 11.5% less than men. Since this estimate accounts for average differences between men and women, it is an estimation of the unexplained gender pay gap. Glass ceiling effect "The popular notion of glass ceiling effects implies that gender (or other) disadvantages are stronger at the top of the hierarchy than at lower levels and that these disadvantages become worse later in a person's career." In the United States, women account for 52% of the overall labor force, but make up only three percent of corporate CEOs and top executives. Some researchers see the root cause of this situation in the tacit discrimination based on gender, conducted by current top executives and corporate directors (primarily male), and "the historic absence of women in top positions", which "may lead to hysteresis, preventing women from accessing powerful, male-dominated professional networks, or same-sex mentors". The glass ceiling effect is noted as being especially persistent for women of color. According to a report, "women of colour perceive a 'concrete ceiling' and not simply a glass ceiling". In the economics profession, it has been observed that women are more inclined than men to dedicate their time to teaching and service. Since continuous research work is crucial for promotion, "the cumulative effect of small, contemporaneous differences in research orientation could generate the observed significant gender difference in promotion". In the high-tech industry,