Statistics are used to indicate disadvantages faced by women in science, and also to track positive changes of employment opportunities and incomes for women in science. Women appear to do less well than men (in terms of degree, rank, and salary) in the fields that have been traditionally dominated by women, such as nursing. In 1991 women attributed 91% of the PhDs in nursing, and men held 4% of full professorships in nursing. In the field of psychology, where women earn the majority of PhDs, women do not fill the majority of high rank positions in that field. Women's lower salaries in the scientific community are also reflected in statistics. According to the data provided in 1993, the median salaries of female scientists and engineers with doctoral degrees were 20% less than men. This data can be explained as there was less participation of women in high rank scientific fields/positions and a female majority in low-paid fields/positions. However, even with men and women in the same scientific community field, women are typically paid 15–17% less than men. In addition to the gender gap, there were also salary differences between ethnicity: African-American women with more years of experiences earn 3.4% less than European-American women with similar skills, while Asian women engineers out-earn both Africans and Europeans. Women are also under-represented in the sciences as compared to their numbers in the overall working population. Within 11% of African-American women in the workforce, 3% are employed as scientists and engineers. Hispanics made up 8% of the total workers in the US, 3% of that number are scientists and engineers. Native Americans participation cannot be statistically measured. Women tend to earn less than men in almost all industries, including government and academia. Women are less likely to be hired in highest-paid positions. The data showing the differences in salaries, ranks, and overall success between the genders is often claimed to be a result of women's lack of professional experience. The rate of women's professional achievement is increasing. In 1996, the salaries for women in professional fields increased from 85% to 95% relative to men with similar skills and jobs. Young women between the age of 27 and 33 earned 98%, nearly as much as their male peers. In the total workforce of the United States, women earn 74% as much as their male counterparts (in the 1970s they made 59% as much as their male counterparts). Claudia Goldin, Harvard concludes in "A Grand Gender Convergence: Its Last Chapter" – "The gender gap in pay would be considerably reduced and might vanish altogether if firms did not have an incentive to disproportionately reward individuals who labored long hours and worked particular hours."