Methodology

Discover which universities around the world are the best for your chosen subject with the QS World University Rankings by Subject 2021

The QS World University Rankings by Subject 2021 cover a total of 51 disciplines, grouped into five broad subject areas.

The QS World University Rankings by Subject are compiled annually to help prospective students identify the leading universities in a particular subject. Research citations, along with the results of major global surveys of employers and academics are used to rank universities. More information about this year’s methodology is available.

Craig OCallaghan

Updated November 3, 2021 Updated November 03

The QS World University Rankings by Subject ranks the world’s top universities in individual subject areas, covering 51 subjects. The rankings aim to help prospective students identify the world’s leading schools in their chosen field in response to high demand for subject-level comparisons.

Each of the subject rankings is compiled using four sources. The first two of these are QS’s global surveys of academics and employers, which are used to assess institutions’ international reputation in each subject. The second two indicators assess research impact, based on research citations per paper and h-index in the relevant subject. These are sourced from Elsevier’s Scopus database, the world’s most comprehensive research citations database. 

These four components are combined to produce the results for each of the subject rankings, with weightings adapted for each discipline.

1. Academic reputation

QS’s global survey of academics has been at the heart of the QS World University Rankings® since their inception in 2004. In 2021, the QS World University Rankings by Subject draws on responses from over 100,000 academics worldwide.

Having provided their name, contact details, job title and the institution where they are based, respondents identify the countries, regions and faculty areas they are most familiar with, and up to two narrower subject disciplines in which they have expertise. For each of the (up to five) faculty areas they identify, respondents are asked to list up to 10 domestic and 30 international institutions which they consider to be excellent for research in the given area. They are not able to select their own institution.

For the QS World University Rankings by Subject, the results of the survey are filtered according to the narrow area of expertise identified by respondents. While academics can select up to two narrow areas of expertise, greater emphasis is placed on respondents who have identified only one.

2. Employer reputation

The QS World University Rankings are unique in incorporating employability as a key factor in the evaluation of international universities. In 2021, the QS World University Rankings by Subject draws on nearly 50,000 survey responses from graduate employers worldwide.

The employer reputation survey works on a similar basis to the academic one, but without the channelling for different faculty areas. Employers are asked to identify up to 10 domestic and 30 international institutions they consider excellent for the recruitment of graduates. They are also asked to identify the disciplines from which they prefer to recruit. By examining the intersection of these two questions, we can infer a measure of excellence in a given discipline.

3. Research citations per paper

For the QS World University Rankings by Subject we measure citations per paper, rather than citations per faculty member. This is due to the impracticality of reliably gathering faculty numbers broken down by discipline for each institution.

A minimum publication threshold is set for each subject to avoid potential anomalies stemming from small numbers of highly cited papers. Both the minimum publications threshold and the weighting applied to the citations indicator are adapted in order to best reflect prevalent publication and citation patterns in a given discipline. All citations data is sourced from the Scopus, spanning a five-year period.

4. H-index

Since 2013, a score based on ‘h-index’ has also been incorporated in the QS World University Rankings by Subject. The h-index is a way of measuring both the productivity and impact of the published work of a scientist or scholar. The index is based on the set of the academic’s most cited papers and the number of citations that they have received in other publications.

The h-index can also be applied to the productivity and impact of a group of scientists, such as a department, university or country, as well as a scholarly journal. The index was suggested by Jorge E. Hirsch, a physicist at UCSD, as a tool for determining theoretical physicists’ relative quality, and is sometimes called the Hirsch index or Hirsch number.

How are large research collaborations assessed?

In 2016, QS introduced an improvement to the way research papers with authors from an exceptionally large number of institutions are assessed. Situations such as these occur most frequently in scientific subjects such as high-energy physics, cosmology, or genomics, where large-scale international collaborations are common.

If each institution involved in papers such as these receives full credit for the citations, even very important and worthwhile papers can end up having a disproportionately large impact on the ranking results. Yet it is equally undesirable to give each institution a share of the credit, as this could discourage research collaborations among groups of any size.

With the support of the QS Global Academic Advisory Board, the solution adopted was to omit any paper with more than 99.9% of the average number of institutional affiliations for the subject in question. This replaces the previous approach of omitting all papers with more than 10 institutional affiliations, which unfairly penalised certain scientific fields, such as medicine.

Weightings

As research cultures and publication rates vary significantly across academic disciplines, the QS World University Rankings by Subject applies a different weighting of the above indicators in each subject. For example, in medicine, where publication rates are very high, research citations and the h-index account for 25% of each university’s total score. On the other hand, in areas with much lower publication rates such as history, these research-related indicators only account for 15% of the total ranking score. Meanwhile in subjects such as art and design, where there are too few papers published to be statistically significant, the ranking is based solely on the employer and academic surveys.

Further details can be found on the QS Intelligence Unit website. 

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This article was originally published in February 2017 . It was last updated in November 2021

Written by

As editor of TopUniversities.com, Craig oversees the site's editorial content and network of student contributors. He also plays a key editorial role in the publication of several guides and reports, including the QS Top Grad School Guide.

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