Year of Publication



Martin School of Public Policy and Administration

Executive Summary

In 2004, with a participation rate of 59.2 percent, women represented 46 percent of the total U. S. labor force. This same year, women earned an average of $573 per week, approximately 80 percent of men’s median weekly earnings. It is rarely disputed that a gender wage gap exists; rather it is the cause of this differential that is often the subject of debate. Empirical evidence indicates that the wage differential can be attributed to factors such as differences in education, labor market experience, and occupational choice.

Research has consistently shown that increases in educational attainment will lead to positive labor market returns. However, such positive returns to education are not always the same for women and men. For example, a stark contrast exists between the earnings of women and men who have earned a vocational or technical certificate or degree. This can be attributed to a high level of occupational differentiation by gender among those with an associate’s degree (61.1 percent) (Wootten, 1997, 18). Women remain clustered in traditionally female educational programs such as childcare, administrative assistance, nursing assistance, and cosmetology. These low-wage careers offer few opportunities for advancement and make the prospect of economic security and self-sufficiency quite difficult. Men who enter vocational or technical programs, however, enroll in programs that lead to higher wage careers in which true economic self-sufficiency is an attainable goal.

Historically, the increase in pay equity between men and women can be linked to the increase in women’s access to traditionally male jobs (Cohn, 2001, 121). The intersection between the gender pay gap and occupational segregation by gender is one that deserves further exploration. However, it is not certain whether the pursuit of non-traditional jobs by women will guarantee that they will earn a wage equivalent to that of their male counterparts. Sex discrimination within the field, evidenced by an unequal wage, may act as a barrier for a woman’s entry.

Exploring whether female workers earn less than comparable male workers within the same narrowly defined occupational category will have potential implications for the promotion of women into non-traditional occupations. The profession chosen to be analyzed in terms of the equality of wages between its male and female workers was diesel mechanics, a male dominated occupation that currently maintains a steady level of demand and pays a good wage.

In 2004, there were 325,000 workers employed as bus and truck mechanics and diesel mechanic specialists, 2,000 of which were women (0.6 percent).

According to the U.S. Department of Labor, this is one of the most gender segregated occupations in the country. Over the past decade, companies across the nation have struggled to recruit and retain qualified and experienced diesel technicians. It is estimated that the nation is suffering from a shortage of up to 45,000 diesel technicians (Kelley, 2001, 26). If the number of diesel technicians entering the workforce continues to decline, it will present a significant problem. The demand for diesel technicians provides an excellent opportunity for women to enter the field. While women search for higher paying jobs and employers of diesel technicians search for qualified help, a potential connection between the two could be made. Exploring the wage differential between men and women in this profession may suggest why the supply of female diesel technicians remains low. Evidence of a wage gap, or lack thereof, will suggest possible policy implications for addressing the diesel technician shortage.

Based on prior research regarding the existence of the gender wage gap, the hypothesis that will be tested in this analysis is, “Employed as bus and truck technicians or diesel engine specialists, women earn a statistically significant lower hourly wage than men.” If the hypothesis holds, it will suggest a potential barrier for women’s entry into this occupation. If the hypothesis is rejected, it will suggest a potential point of interest in introducing women into the field of diesel mechanics.

A quantitative research analysis was designed to investigate the research question. To analyze the wage differential between men and women, a multiple regression analysis was conducted. This statistical tool was used to explore the relationship between hourly wage and gender, while controlling for additional explanatory variables. Education, race, region, number of hours worked, labor market experience are examples of variables that were included in the regression equation.

The sample was drawn from the 5 percent sample of the United States Census 2000. The dependent variable was the natural logarithm of hourly wage. The analysis included a carefully selected group of independent variables. The explanatory variables that were chosen to be included in the regression model were as follows: age, sex, educational attainment, Hispanic or Latino origin, marital status, race, potential work experience, and region of the country in which the respondent worked.

According to the adjusted R-squared value, only 6.3 percent of the variation in hourly wage in the sample could be explained by the independent variables. This is quite low and it indicates that the wage of diesel technicians is correlated to some other factor or factors, such as productivity or experience within the field of diesel mechanics, which were not captured by the regression equation. Of the independent variables, using a 95 percent confidence level, all were statistically significant with the exception of sex, race, and potential work experience. Therefore, based on the sample, sex was not a statistically significant predictor of the variance in hourly wage.

The creation of interaction terms to be included in a second regression model provided a more accurate estimation of the relationship between the independent and dependent variables. An interaction term is simply a variable representing the product of two explanatory variables from the multiple regression model. In this case, two different variables were interacted with sex. The new variables were the interaction between having a high school degree and sex (“hsedxsex”) and the interaction between having greater than a high school degree and sex (“highedxsex”). The creation of these variables allowed for the effects of gender on hourly wage to change as the level of educational attainment changes.

According to the regression output, at the .05 level, the interaction between sex and earning a high school degree is not a statistically significant predictor of the variance in hourly wage. In this sample, the returns to a high school degree, in terms of hourly wage, do not vary by gender. The interaction between educational attainment above a high school degree and sex is also not correlated to hourly wage at the .05 level. However, the p-value of .065 indicates that there is a marginally significant difference in hourly wage for men and women who have attained an education above a high school degree. Using a 90 percent confidence interval (p-value ≤.10), the effect of high educational attainment on hourly wage varies according to the gender of the worker. The positive coefficient on the variable “highedxsex” indicates that women who pursue degrees above the high school level can expect to get greater returns, in terms of hourly wage, than men. This is encouraging for women who seek higher education in that they can expect a smaller gender wage differential as their level of education increases.

Following the discussion of the limitations to this research, recommendations based on the findings of this analysis can be made. Disseminating the information that women earn an equal wage in the traditionally male dominated occupation of diesel mechanics is crucial. Recruitment of women to the field of diesel mechanics can begin with letting women know that the data shows that there is not a statistically significant difference between the average male and female wage.

Since the enactment of Temporary Assistance to Needy Families (TANF), the welfare reform act of 1996, employment among single mothers has increased (Meyer, 1999). The goal of TANF is for recipients to achieve self-sufficiency and economic security through work. The potential exists for a powerful connection to be made between TANF’s welfare to work programs and women’s entry into nontraditional occupations such as diesel mechanics. Women moving from welfare to work are looking for job security and a steady wage, characteristics of the skilled-trade professions (Borrego, 2002, 30). The evidence provided does support the notion that diesel mechanics is a potential profession for women in which they can expect to earn a wage comparable to that earned by a man.

Further research that explores wage differentials in other male dominated occupations would allow for conclusions to be drawn regarding the relationship between women and wages in nontraditional occupations. Even though gaining entry into nontraditional jobs may be difficult for women, perhaps once they are trained and educated, they can expect a wage equal to that of their male counterparts. This could be a great incentive for women to pursue nontraditional occupations. A broader study of women’s wages in nontraditional occupations is necessary to shed more light on this issue. What can be derived from this research is that the evidence provided does support the notion that diesel mechanics is a potential profession for women in which they can expect to earn a wage comparable to that earned by men.