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National Science Foundation National Center for Science and Engineering Statistics
Trends in Interdisciplinary Dissertation Research: An Analysis of the Survey of Earned Doctorates

Trends in Multiple Fields by Knowledge Domain


The Survey of Earned Doctorates includes a list of fields of study from which individuals can select codes corresponding to the fields of their dissertation research. This list groups the different fields of study codes into 12 knowledge domains, which are listed in the first column of table 2. Table 2 indicates the prevalence of each of these field categories among individuals who conducted both single-discipline and interdisciplinary doctoral research. This table thus allows us to compare the prevalence of each knowledge domain among doctorate earners who reported only one field and those who reported multiple fields. Table 2 illustrates that fields in the life sciences were the most commonly reported dissertation research fields, followed by engineering fields, then education fields. Relatively few doctorate earners reported dissertation research in communications, miscellaneous fields not elsewhere classified, business management and administration, mathematics, and computer and information sciences.

TABLE 2. Fields reported as sole field of a single-discipline dissertation or a primary field of an interdisciplinary dissertation: 2001–08
dissertations: sole field
Interdisciplinary dissertations:
primary field
Field Number Percent Number Percent
Total 222,177 100.0 88,293 100.0
Business management and administration 5,979 2.7 2,437 2.8
Communications 2,122 1.0 1,227 1.4
Computer and information sciences 6,958 3.1 1,646 1.9
Education 31,616 14.2 11,890 13.5
Engineering 33,354 15.0 11,866 13.4
Humanities 25,799 11.6 11,018 12.5
Life sciences 44,560 20.0 23,826 27.0
Mathematics 6,714 3.0 1,823 2.1
Miscellaneous fields not elsewhere classified 4,113 1.9 2,051 2.3
Physical sciences 23,606 10.6 7,975 9.0
Psychology 17,326 7.8 5,086 5.8
Social sciences 20,030 9.0 7,448 8.4

NOTE: Percentages may not sum to 100% due to rounding.

SOURCE: National Science Foundation/National Center for Science and Engineering Statistics, Survey of Earned Doctorates.

  Table 2 Source Data: Excel file

Table 2 shows that there is similarity in the frequencies in which each of these field categories was reported as a primary research field for both single-discipline and multidiscipline doctorate earners. The percentage of doctorate earners who reported primary fields of interdisciplinary dissertations in each knowledge domain is somewhat similar to the percentage of single-discipline doctorate earners who reported a dissertation in each of these knowledge domain categories. This suggests that interdisciplinary doctorate earners are distributed among each of the knowledge domains in a similar fashion as single-discipline doctorates. The most notable difference is in the life sciences: the percentage of interdisciplinary doctorates who reported a primary field in the life science was 7.0% higher than the percentage of single-discipline doctorates who reported life science fields.

Table 2 also indicates that doctorate earners in the life sciences were the most likely to report conducting an interdisciplinary dissertation. Given this, we explored this category of fields in more detail to get a better sense of which fields are most likely to be reported in conjunction with other fields. The taxonomy of fields used in the Survey of Earned Doctorates further divides the general life sciences category into three subcategories: agricultural and natural resource sciences, biological and biomedical sciences, and health sciences. This supplemental analysis of the subcategories of the life sciences indicates that a majority of the interdisciplinary dissertations in life sciences had a primary field within the biological and biomedical sciences (19.4% of all interdisciplinary dissertations, based on primary field reported). Dissertations in agricultural and natural resource sciences made up 3.4% of all interdisciplinary dissertations, and dissertations in health sciences constituted 4.2% of the interdisciplinary dissertations. These percentages are similar to the percentages of respondents with a dissertation in a single discipline who reported dissertation research in these fields. Thus the high numbers of interdisciplinary dissertations in life science (seen in table 2) is to some extent driven by the fact that there are simply many individuals who earn doctorates in the fields of biological and biomedical sciences.

We next calculated which percentage of each knowledge domain's dissertations were interdisciplinary in order to determine which fields are most likely to produce interdisciplinary dissertations, regardless of the overall number of individuals who earn doctorates in those discipline areas. Table 3 documents the total number of dissertations and the number of interdisciplinary dissertations, broken down by the knowledge domain of the primary research field. This table also indicates the percentage of dissertations in a particular knowledge domain that are interdisciplinary. In this table, several of the knowledge domain categories have been broken down into subcategories that are listed in the survey's list of codes. These components help to provide additional detail about the distribution of individuals within each of these categories.

TABLE 3. Interdisciplinary dissertations, by knowledge domain of primary field: 2001–08
Primary dissertation research
field categories
Dissertations in
category (number)
Interdisciplinary dissertations
Number Percent
Total 310,470 88,293 28.4
Business management and administration 8,416 2,437 29.0
Communications 3,349 1,227 36.6
Computer and information sciences 8,604 1,646 19.1
Education 43,506 11,890 27.3
Education research and administration 33,451 8,573 25.6
Teacher education and teaching fields 10,055 3,317 33.0
Engineering 45,220 11,866 26.2
Humanities 36,817 11,018 29.9
Foreign languages and literature and letters 14,485 4,916 33.9
History 7,275 2,053 28.2
Other humanities 15,057 4,049 26.9
Life sciences 68,386 23,826 34.8
Agricultural and natural resource sciences 8,176 3,010 36.8
Biological and biomedical sciences 47,312 17,140 36.2
Health sciences 12,898 3,676 28.5
Mathematics 8,537 1,823 21.4
Miscellaneous fields not elsewhere classified 6,164 2,051 33.3
Physical sciences 31,581 7,975 25.3
Earth, ocean, and atmospheric sciences 6,984 2,181 31.2
Physics and chemistry 24,597 5,794 23.6
Psychology 22,412 5,086 22.7
Social sciences 27,478 7,448 27.1

SOURCE: National Science Foundation/National Center for Science and Engineering Statistics, Survey of Earned Doctorates.

  Table 3 Source Data: Excel file

The overall rate of interdisciplinary doctoral research for all fields was 28.4%. The table shows the incidence of interdisciplinary dissertations as a percentage of all dissertations within a specific knowledge domain. Three domains had a percentage of interdisciplinary research above 36.0%: the agricultural and natural resource sciences fields (a subcategory of life sciences) had 36.8% interdisciplinary dissertations, the communications fields had 36.6% interdisciplinary dissertations, and the biological and biomedical sciences (another subcategory of the life sciences) had 36.2% interdisciplinary dissertations. Several other areas had rates of interdisciplinary research above 30%. The lowest incidence of interdisciplinary research was for the computer and information sciences fields (19.1%). Persons earning mathematics doctorates were also relatively less likely to report interdisciplinary dissertations (21.4%). The third lowest rate of interdisciplinary research was in psychology (22.7%).

Figure 1 Figure. illustrates the changes in rates of interdisciplinary dissertations over time for each knowledge domain. Because the wording of the question about respondents' fields of research was changed in 2004, we compared the average rates of reporting interdisciplinary doctoral research from before and after this methodological change (2001–03 versus 2004–08). This figure shows the rate changes for subcategories of the education, humanities, life sciences, and physical sciences knowledge domains, rather than aggregate numbers.

The comparisons in figure 1 Figure. show that 10 of the 18 field areas had higher rates of interdisciplinary research in the later years of the survey than in 2001–03. One field had no increase, and the remaining seven showed decreases over time in the rate of interdisciplinary dissertation research. The largest decrease in the rate of interdisciplinary dissertations was within the education research and administration fields, wherein they decreased in prevalence by 5.6%. Interdisciplinary dissertations in psychology, the field category with the second-greatest decrease in interdisciplinary dissertations, decreased by 3.3%. History showed no increase or decrease in the rate of interdisciplinary dissertations over time.

The "other humanities" category, which is a diverse category that consists of a variety of fields—including American studies, music, drama, art history, religious studies, and philosophy—experienced the largest increase in the rate of interdisciplinary dissertations (7.4%). Interdisciplinary doctoral research also increased substantially in the engineering fields (5.1%) and the humanities category consisting of foreign languages and literature and letters (4.2%).

Figure 1 Figure. demonstrates that some fields spanning both the sciences and humanities have experienced increased rates of interdisciplinary doctoral research and others have experienced decreases. It is unclear from these data alone what has inspired the varied outcomes—for example, relatively large increases were seen over time in some of the humanities, engineering, and physics and chemistry, but the decreased rates of interdisciplinary doctoral research were seen within categories such as education research and administration and psychology. Also, the figure illustrates that fields that initially had high rates of interdisciplinary dissertations are not necessarily fields that experienced the greatest increases over time. In fact, several of the highest rates of increase are in field areas that had relatively low rates of interdisciplinary research to begin with (i.e., other humanities, physics and chemistry, and engineering).

Trends in Interdisciplinary Dissertation Research: An Analysis of the Survey of Earned Doctorates
Working Paper | NCSES 12-200 | April 2012