How U.S. News Calculated the Best Global Universities Subject Rankings
Find out how U.S. News determined the top universities in the world by field of study.
By Robert Morse and Alexis Krivian
Oct. 23, 2017, at 9:00 p.m.
In addition to ...
How U.S. News Calculated the Best Global Universities Subject Rankings
Find out how U.S. News determined the top universities in the world by field of study.
By Robert Morse and Alexis Krivian
Oct. 23, 2017, at 9:00 p.m.
In addition to rankings of the world's top 1,250 universities overall and by region and country, the fourth annual U.S. News Best Global Universities rankings include an examination of the leaders in key academic subject areas. U.S. News used a separate methodology to publish the top global universities in 22 subject areas. The subject rankings are powered by Clarivate Analytics InCites. Clarivate provided the data and metrics used in the rankings, and the bibliometric data were based on the Web of Science.
These subject-specific rankings – which are not of academic majors, departments or specific schools at universities, such as business or medical schools – are based on academic research performance in those subjects. U.S. News has used various bibliometric measures, including publications and citations, as well as indicators for global and regional reputation in each specific subject.
In many cases, an institution that had a strong focus on a certain subject was ranked in that subject but was excluded from the overall Best Global Universities rankings encompassing the top 1,250 universities worldwide. In total, 125 universities were included in the subject rankings but not in the overall top 1,250 ranked universities. Five countries – Peru, Ghana, Indonesia, Malawi and Vietnam – were represented in the subject rankings but not among the 74 countries in the overall rankings.
Ranking Indicators
The bibliometric indicators are based on data from the Web of Science for the five-year period from 2011-2015. The Web of Science is a web-based research platform that covers more than 18,000 of the most influential and authoritative scholarly journals worldwide in the sciences, social sciences, and arts and humanities. The 22 subject fields used in the analysis came from subject schema in Clarivate Analytics InCites, which uses the content and citation indicators from the Web of Science. Publications are limited to those published between 2011 and 2015. However, the citations to those papers come from all publications, including the most recent data available. For the 2018 rankings, this cutoff date was May 30, 2017. It is necessary to use a slightly older window of publication to allow for citations to accumulate and provide statistically relevant results.
The first step in producing the subject rankings was to create the total universe of schools that could be ranked in each field. Depending on the subject, the number of universities ranked ranged from a low of 206 for immunology to a high of 1,011 in chemistry – see the Total number of universities ranked column in the table below. The size of the ranking pool in each of the 22 subject areas – except in two cases, microbiology and space science – was determined by the number of universities that had a published paper count of 250 or more in the 2011-2015 time period in the subject area; see the Number of universities with >250 papers in 2011-2015 column in the table below. In microbiology and space science, the paper threshold was 150 and 200 papers, respectively, for the 2011-2015 time period.
U.S. News studied how many papers each university had published in each of the 22 subject areas and determined that the rankings could be extended in some areas, since many universities had published far more than 500 papers in the 2011-2015 period.
For the 2018 rankings, U.S. News worked with Clarivate Analytics' bibliometric experts to increase the number of ranked universities in four fields. The number of ranked universities published in chemistry, clinical medicine, engineering and physics increased from 400 to 600. The number of ranked schools published in the other 18 fields remained the same as last year. This meant that 6,800 universities were ranked in 22 subjects in the 2018 rankings, which is a 13.3 percent increase from the 6,000 ranked last year. Many universities appear in more than one subject ranking. For example, 14 universities appear in all 22 subject rankings, 19 appear in 21 subject rankings and 18 appear in 20 subject rankings.
For the 2018 edition, four fields each list 600 ranked universities, four each list 400 schools and 14 fields each list 200 institutions.
The table below shows the number of universities that published more than 250 papers and those that published more than 500 papers in each subject area from 2011 to 2015; the total number of universities ranked in each subject; and the number of schools U.S. News published rankings for in each subject area. Space science
Number of universities with >250 papers in 2011-2015: 212
Number of universities with >500 papers in 2011-2015: 99
Total number of universities ranked: 213
Number of ranked universities published by U.S. News: 200
The next step was to calculate the 22 separate subject rankings using the ranking factors U.S. News selected. U.S. News changed the methodology used in all 22 of the 2018 Best Global Universities subject rankings by adding ranking factors that are also used in the overall rankings. In all 22 subject rankings, U.S. News added the percentage of a school's total papers in that subject that had international co-authors.
With the exception of arts and humanities, for all fields U.S. News added two new ranking factors that measure scientific excellence – the total number of highly cited papers in the top 1 percent of their respective subject fields and the percent of a university's total papers in that subject that are among the top 1 percent of most cited papers in that subject – each with a 5-percent weight. This means that all 22 subject rankings now use 11 ranking factors. As a result of the additional rankings indicators, the weights used in the 2018 Best Global Universities subject rankings for some of the ranking indicators were changed from the prior edition.
The new percentage of a school's total papers in that subject that had international co-authors is weighted 5 percent for all the subject rankings, except arts and humanities, where it was weighted 2.5 percent. The existing international collaboration ranking indicator's weight was also reduced from 10 percent to 5 percent for all the subject rankings, except arts and humanities, where its weight was reduced from 5 percent to 2.5 percent.
With the addition of the two new indicators – total number of highly cited papers in the top 1 percent of their respective fields and the percent of a university's total papers that are among the top 1 percent of most cited papers in their respective fields – U.S. News reduced the weights of two other indicators.
For all the subject fields except arts and humanities, the weight of the number of publications that are among the 10 percent most cited is now 12.5 percent in the soft sciences, down from 17.5 percent, and 10 percent in the hard sciences subject rankings, reduced from 15 percent. The percentage of total publications that are among the 10 percent most cited indicator is also now weighted 5 percent, down from 10 percent, in both the soft and hard sciences subject rankings for all fields except the arts and humanities. Each indicator used in the subject rankings was based on bibliometric and global and regional reputation data compiled for that specific subject. For example, for the Best Global Universities for Clinical Medicine ranking, each of the 11 ranking factors used in the calculations was based on data and values for clinical medicine.
The subject rankings methodology differs in a number of ways from the one U.S. News used to produce the overall Best Global Universities rankings of the top 1,250 schools.
First, U.S. News tailored the subject ranking methodology to the different publication characteristics of the soft sciences compared with the hard sciences. As listed below, the soft sciences are computer science, economics and business, engineering, mathematics, and social sciences and public health. The hard sciences are the remaining 16 subject areas, excluding arts and humanities. Arts and humanities:
Arts and humanities
Soft sciences:
Computer science
Economics and business
Engineering
Mathematics
Social sciences and public health
Hard sciences:
Agricultural sciences
Biology and biochemistry
Chemistry
Clinical medicine
Environment/ecology
Geosciences
Immunology
Materials science
Microbiology
Molecular biology and genetics
Neuroscience and behavior
Pharmacology and toxicology
Physics
Plant and animal science
Psychiatry/psychology
Space science
U.S. News has developed a distinct ranking methodology for arts and humanities.
The arts and humanities methodology takes into account key characteristics of that field, in which publications play a significantly smaller role. That means that for the arts and humanities ranking, the number of publications or other indicators that relate to publications and citations were weighted far less than they were in the other subject areas.
This also means that the conferences and books indicators were used and heavily weighted but weren't used in the other subject rankings, and that both global research reputation and regional research reputation were weighted more heavily than in the other subject rankings. The use of citation analysis within the hard sciences is well established. However, in the soft sciences, the relationship between citations and performance is less clear. There are a number of reasons for this.
First, unlike the hard sciences, journal articles are often not the main method of communication of research, and citation rates to the articles may be low. Second, in the social sciences and economics and business, when a scholar cites another work, it is frequently a point of debate or discussion.
This is in contrast with the hard sciences, where the reason for citing another work is usually one of utility or influence. In the case of mathematics, although a journal article is the main method of communication, citations tend to take a longer time to accumulate than other fields and the overall citation rate to mathematics papers tends to be quite low.
These reasons do not negate the use of citation analysis for research evaluation, but they decrease confidence in the robustness of the results. Therefore, U.S. News lowered the weights assigned to these citation indicators in the soft sciences to reflect the lower confidence.
The table below lists the weights and factors used to compute the 22 subject rankings, with related indicators grouped together. For a detailed explanation of each ranking factor, please read "How U.S. News Calculated the Best Global Universities Rankings." Space science: Journals focused on studying the universe make up the space science category. From astronomy and astrophysics to celestial bodies and space exploration, publications within this category deal with the study of everything in outer space. How the Subject Scores and Numerical Rankings Were Calculated
To arrive at a school's rank in each of the 22 subjects, the subject scores were calculated using a combination of the weights and z-scores for each of the ranking indicators used in each subject ranking. In statistics, a z-score is a standardized score that indicates how many standard deviations a data point is from the mean of that variable. This transformation of the data is essential when combining diverse information into a single ranking because it allows for fair comparisons between the different types of data.
Some of the indicators were highly skewed, so the logarithmic transformation of the original values were used. These indicators were:
Publications.
Total citations.
Books.
Conferences.
Number of publications that are among the 10 percent most cited.
Number of highly cited papers that are among the top 1 percent most cited in their respective fields.
International collaboration.
Global research reputation.
Regional research reputation.
The logarithmic transformation rescaled the data and allowed for a more normalized and uniform spread across each of the indicators. After the indicators were normalized, the z-scores for each indicator were calculated in order to standardize the different types of data to a common scale. To reach a school's subject score, the calculated z-scores for each of the ranking indicators were weighted using the weights described earlier. U.S. News determined the weights based on our judgment of the relative importance of the ranking factors and in consultation with Clarivate Analytics' bibliometric experts.
The subject score was calculated by summing the school's weighted values for the ranking indicators in that subject. The minimum score from the total ranking universe for that subject was then subtracted from each of the scores to make zero the lowest possible score.
The scores were then rescaled by multiplying the ratio between the overall performance of each university in that subject and the highest-performing university by 100. This forced the scores to fall on a 0-100 scale, with the highest-performing school earning a subject score of 100.
Of the total number of universities ranked for each of the 22 subject areas, U.S. News then used their weighted subject score to numerically rank them in descending order for each subject area. Each school's subject score was rounded to one decimal place to increase variance between scores and to minimize the occurrence of ties. U.S. News then published either the top-ranked 200, 400 or 600 schools in each subject area.
In addition, in each of the 22 subject areas, the 11 ranking indicators used for each subject area's ranking received a separate numerical rank – such as publications, total citations and global research reputation – based on their z-score for that indicator in that subject area. The highest-scoring university for each of the ranking indicators received a rank of 1, and the lowest-scoring university received a rank ranging from 206 in immunology to 1,011 in chemistry. Ties were allowed.
The one exception is the regional research reputation rank. The regional research reputation numerical rankings are calculated based on the schools within each of the six United Nations regions. Those six regions are Africa, Asia, Australia/New Zealand, Europe, Latin America and North America.
This means the regional reputation numerical ranking in any of the 22 subject area can have up to six No. 1 schools, or one for each region. This comparison enables users to determine which schools have the strongest regional research reputation among the schools in their region in that subject area.
The numerical ranks for each of the 11 ranking indicators are published on
usnews.com
for each school in each of the 22 subject areas. Some schools in the subject areas have ranking indicators with numerical ranks greater than the 200, 400 or 600 schools that are published in each subject.
Readers can use the numerical ranks published for each ranking indicator to determine the relative position of each school in that indicator, depending on the subject, with 1 being the highest. The numerical indicator ranks were not used to calculate the subject score.
Data Collection
The data and metrics used in the rankings were provided by Clarivate Analytics InCites. The bibliometric data were based on the Web of Science.
Tags: #globaluniversities, #rankings, #education, #research, #academics, #globalization, #world, #internationalstudents, #studyabroad
Robert Morse is chief data strategist at U.S. News, where he develops the methodologies and surveys for annual education rankings, including Best Colleges and... full bio »
Alexis Krivian is a data analyst at U.S. News. Searches :
https://www.usnews.com/education/best-global-universities/articles/subject-rankings-methodology