Examining Gender Salary Gaps for Faculty at the University of South Dakota
South Dakota Council for Higher Education
Michael Allgrunn and Kathryn Birkeland*
*Allgrunn: Corresponding author, Department of Economics, University of South Dakota, Mike.Allgrunn@usd.edu. Birkeland: Department of Economics, University of South Dakota, Kathryn.Birkeland@usd.edu. We thank Alan Aldrich, USD COHE Chapter President, for collecting and providing the data used in this report.
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Introduction This study was conducted for the South Dakota Council for Higher Education (COHE) with the goal of describing whether faculty salaries at the University of South Dakota (USD) vary based on gender. What follows is a descriptive analysis of faculty salaries from 2011-2014. We are not prescribing any particular policy changes related to our findings.
Data Our data was supplied by COHE and contains data for faculty unit members employed at USD in the 2011 to 2014 academic years.1 The results here include tenure-track (assistant, associate, and full professors) and lecturer (instructor, lecturer, and senior lecturer) faculty.2 Faculty members with administrative appointments are excluded from the bargaining unit and thus are not part of the dataset. We will report on the gender salary differences for faculty in the following colleges and schools: Arts & Sciences, Business, Education, Fine Arts, and Health Sciences.3 This data represents a population, not a sample, so discussions of statistical significance are not appropriate.4 We do not have data on other variables which might be correlated with gender and/or salary. Faculty performance is likely correlated with salary, but objective measures of performance are difficult to imagine and do not exist in our dataset. We are not aware of any reason to suspect that gender is correlated with faculty performance at USD. If it were, the differences shown here could be overstated or understated. Variables on race, years in rank, experience, and degrees held are not in the dataset. If any of these are correlated with both salary and gender, the differences shown in this report could be overstated or understated. Our dataset does not include faculty with administrative roles, we also cannot comment on any gender differences in administrative appointments. Our salary figures are the base salary and do not include any overload or supplemental pay.
Method We use linear regression to calculate the salary difference by gender with controls for rank and school. The basic framework is: đ?‘ đ?‘Žđ?‘™đ?‘Žđ?‘&#x;đ?‘Śđ?‘– = đ?›˝0 + đ?›˝1 ∗ đ?‘“đ?‘’đ?‘šđ?‘Žđ?‘™đ?‘’đ?‘– + đ?œˇđ?‘‹đ?‘– + đ?‘˘đ?‘– where salary is the faculty salary measure, female is an indicator variable (=1 for females, =0 otherwise), and X is a vector of control variables related to rank and school.
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Faculty unit members are employees of the Board of Regents who are part of the collective bargaining unit. See the Agreement Between the South Dakota Board of Regents and the Council of Higher Education 2013-2016, Appendix A for a description of the bargaining unit. 2 Librarian ranks have not been included in this report due to the low number of faculty in each of those ranks. 3 Other colleges and schools are not included either due to low numbers, or because they are not faculty unit members and thus not in our dataset. 4 The faculty unit members at USD are not a random sample of any larger group of faculty, so our results are not estimates of any population. Rather they are the actual differences for the population of faculty unit members at USD.
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When đ?›˝1 is positive, it indicates a salary difference where females earn more than males, controlling for rank and school variables. When đ?›˝1 is negative, it indicates a salary difference where females earn less than males, controlling for rank and school. When đ?›˝1 is zero, it indicates that female and male salaries are equal, controlling for the other variables of rank and school. We use two different measures of salary. The first is simply the annual salary of the faculty member, which we will refer to as salary below. The second is the salary as a proportion of the Oklahoma Salary Survey and will be referred to as relative salary. Relative salary has the advantage of controlling for salary differences by both academic discipline and rank.
Results We present the results on salary differences in two sections, based on the two different measures of salary. In each section, we also provide the gender gap by school and by rank. Some of the groups measured consist of a relatively small group of faculty, so keep in mind that observed salary differences (or lack thereof) might be explained by the uncontrolled measures (like performance) of a very small number of male or female faculty in a group. Salaries A simple regression of logged annual salary on the female indicator variable measures the difference in salary without considering any other factors. Over the study time period, female salaries are about 16.0% less than male salaries without controlling for any other factors. This type of gap, without other controls, is referred to as the raw salary gap. Adding controls for the different schools, the gender gap shrinks somewhat, with female salaries being 13.7% less than male salaries. Alternatively, the gender gap decreases to 1.8% lower than male salaries after controlling for rank. Controlling for both rank and school reduces the gap to 0.9%. This suggests that the observed difference in salaries by gender is largely explained by differences in academic rank. Of the male observations in our sample, 22.7% are full professors, while only 7.8% of female observations are full professors. By contrast, 46.3% of female observations are instructors, while only 7.7% of male observations are instructors.
Salary gaps percentage gaps (female - male)
0%
raw
school
rank -1.8%
-5%
rank and school -0.9%
salary
-10% -15%
-13.7% -16%
-20%
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Salary Gaps by School In order to examine the size of any gender gap by school, we added school*gender interaction terms. Without controlling for academic rank, the raw salary gap in each of the colleges or schools is as follows: Arts & Sciences Business Education Fine Arts Health Sciences
females earn 20.7% less females earn 21.9% less females earn 4.1% less females earn 6.7% more females earn 4.6% more
The gaps in Arts & Sciences and in Business are large. Gaps in other areas are generally smaller, and in two cases (Fine Arts and Health Sciences) are in the opposite direction than the raw gap, indicating that males earn less than females in those schools. These results do not account for differences in rank, which, as seen above, explained most of the raw gap for USD as a whole. Adding controls for rank changes the salary gaps as follows: Arts & Sciences Business Education Fine Arts Health Sciences
females earn 3.3% less females earn 5.8% less females earn 2.3% more females earn 6.8% more females earn 11.6% more
All schools where the gap was negative become less so, and schools where the gap was positive become more so. Males in Fine Arts and Health Sciences earn 6.8% less and 11.6% less, respectively, than females in the same schools with the same academic ranks. Arts & Sciences females earn 3.3% less than males of the same school and rank. Females in Business earn 5.8% less than males of the same school and rank.
Salary gaps by school percentage gap (female-male)
Arts & Sciences
Business
Education
Fine Arts
Health Sciences
15.0%
11.6%
10.0%
6.7% 6.8%
5.0%
2.3%
4.6%
0.0% -5.0%
-3.3%
-10.0%
-5.8%
-4.1%
-15.0% -20.0% -25.0%
-20.7%
-21.9%
raw
rank controlled
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Salary Gaps by Rank In order to examine the size of any gender gap by rank, we added rank*gender interaction terms. Without controlling for school, the salary gaps by school are: Full Associate Assistant Instructor Lecturer Senior
females earn 5.9% less females earn 6.1% less females earn 4.3% less females earn 13.0% more females earn 24.0% more females earn 10.2% more
Tenure-track females generally earn less than males of the same rank without controlling for school, with a 5.9% gap at full professor, a 6.1% gap at associate, and the 4.3% gap at assistant. The gender gap for Instructors and Lecturer ranks is markedly different, with female instructors earning 13% more than male instructors, and female lecturers earning 24% more than male lecturers. Adding controls for schools, the gender salary gaps by rank are consistently smaller: Full Associate Assistant Instructor Lecturer Senior
females earn 3.8% less females earn 1.5% less females earn 3.3% less females earn 11.3% more females earn 11.5% more females earn 0.4% more
While the salary gaps by rank all shrink, tenure-track females still earn between 1.5% and 3.8% less than tenure-track males, and male instructor and lecturers still earn between 0.4% and 11.5% less than females of similar rank.
Salary gaps by rank Full
Associate
Assistant
Instructor
percentage gap (female-male)
30.0%
Lecturers
Senior
24.0%
25.0% 20.0% 13.0%
15.0% 10.0% 5.0%
11.3%
11.5%
10.2% 0.4%
0.0% -5.0% -10.0%
-5.9%
-3.8%
-1.5% -6.1%
raw
-4.3% -3.3%
school controlled
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Overall, rank and school explains a large portion of raw gender salary gap, but some gaps persist. The sub-groups being compared are small enough that the remaining differences could be explained by the salaries of a very small number of faculty. We cannot identify the extent to which any of these differences might be due to gender discrimination or to other unobserved factors. Relative Salaries One concern with the above results is that we have not fully controlled for differences in market salary by academic discipline. While controlling for School may capture some of these differences, substantial differences can exist between disciplines within a single school. For this reason, we now turn our attention to relative salaries. The Oklahoma State University Faculty Salary Survey by Discipline provides market averages by discipline5, Carnegie classification, and geographic region. Using the 90% Oklahoma Salary numbers for each faculty unit member at USD, we construct relative salaries as the ratio of salary to 90% of the Oklahoma Salary Survey average for each faculty member’s academic discipline. The results are interpreted as percentage point differences.6 Using relative salary, females are paid 7.6 percentage points more than males, a contrast with the findings from our previous salary measure. This raw gender gap does not control for rank or school. Controlling for school reduces this gap to 4.8 percentage points. Controlling for rank reduces the gap to 1.6 percentage points, and controlling for both reduces the gap to 0.4 percentage points.
Relative Salary Gaps percentage point gap (female - male)
8
7.6
7 6 4.8
5 4
relative salary
3 1.6
2 1 0
0.4 raw
school
rank
rank and school
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CIP code For example a gap of -3 percentage points would be interpreted as females earning 87% of the Oklahoma Salary Survey amount compared with males earning 90%. 6
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Relative Salary Gaps by School To examine differences in pay relative to the Oklahoma Salary survey based on gender and school, we added interaction terms. Not controlling for rank, the relative salary gaps by school are: Arts & Sciences Business Education Fine Arts Health Sciences
female salaries are 7.2 percentage points higher female salaries are 5.0 percentage points lower female salaries are 10.0 percentage points higher female salaries are 7.0 percentage points higher female salaries are 2.7 percentage points higher
Females in Fine Arts, Arts & Sciences, Education, and Health Sciences at USD are paid 7.0, 7.2, 10.0, and 2.7 percentage points more, respectively, than males relative to the Oklahoma Survey averages. Females are paid less in Business and the Graduate School (5.0 and 2.5 percentage points, respectively). Controlling for rank, the gender gaps across schools generally shrink: Arts & Sciences Business Education Fine Arts Health Sciences
female salaries are 0.6 percentage points higher female salaries are 10.5 percentage points lower female salaries are 7.1 percentage points higher female salaries are 6.8 percentage points higher female salaries are 1.0 percentage points lower
In Arts & Sciences the relative salary difference is reduced to 0.6 percentage points. The gaps in Education and Fine Arts are somewhat smaller at 7.1 and 6.8, respectively. The gap in Health Sciences falls from 2.7 to -1, and the gap in Business grows from -5 to -10.5, holding school and rank constant.
Relative Salary gaps by school Arts & Sciences
Business
Education
Fine Arts
Health Sciences
percentage point gap (female-male)
15 10
10
7.2
7.1
5
7
6.8 2.7
0.6
0 -1
-5 -5
-10 -10.5
-15 raw
rank controlled
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Relative Salary Gaps by Rank Adding interactions of female and rank allows us to see the gap by rank. Here are the gaps without controlling for schools: Full Associate Assistant Instructor Lecturer Senior Lecturer
female salaries are 0.9 percentage points lower female salaries are 5.2 percentage points higher female salaries are 0.9 percentage points higher female salaries are 5.8 percentage points higher female salaries are 8.2 percentage points higher female salaries are 0.9 percentage points lower
These gaps are generally smaller than found elsewhere. Only Associate, Instructor, and Lecturer ranks show large coefficients, each showing males earn less than females of the same rank. The gap for Lecturers remains large at 10.7 percentage points. Here are the same gaps by rank, but controlling for schools: Full Associate Assistant Instructor Lecturer Senior Lecturer
female salaries are 2.4 percentage points lower female salaries are 4.0 percentage points higher female salaries are 0.2 percentage points higher female salaries are 4.5 percentage points higher female salaries are 10.7 percentage points higher female salaries are 2.4 percentage points lower
There isn’t a clear pattern here. In the Full and Senior Lecturer ranks, where female relative salaries are lower, the school-controlled gaps are somewhat larger. In the other ranks, where male relative salaries are lower, the gap generally shrinks, except for the Lecturer rank, where the gap grows to 10.7 percentage points.
Relative Salary gaps by rank percentage point gap (female-male)
Full
Associate
Assistant
Instructor
Lecturers
12
Senior
10.7
10
8.2
8
5.8
5.2
6
4.5
4
4 2
0.9
0.2
0 -2 -4
-0.9
-0.9 -2.4
-2.4
raw
school controlled
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Overall, the relative salary numbers present a different picture than the salary numbers used previously, with the raw gap indicating females earning 8.8 percent more than males. This gap also shrinks as we add controls for school or rank. There are gender differences in relative salary within ranks and across schools. As in the salary analysis, the sub-groups being compared are quite small, and the remaining differences could be explained by the relative salaries of a very small number of faculty. We cannot identify the extent to which any of the remaining differences are due to discrimination or to other unobserved factors.
Summary Salary differences by rank and school explain a substantial portion of the raw gender gaps among faculty at USD. There are gender gaps in salary and relative salary by rank and by school, but not consistently in the direction of either females or males. The small number of faculty in some groups mean that these results could be sensitive to the salary differences of a small number of faculty in each group, and we encourage caution in drawing conclusions about the salary gap in a particular rank or school. Whether any remaining differences are due to discrimination or to other unobserved factors is not a question that can be answered with the available data.
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