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Common Aggregation Hierarchy (CAH)

The Common Aggregation Hierarchy (CAH) provides a standardised hierarchical aggregation (grouping) of subject codes and terms (developed based upon the HECoS codes and terms) suitable for the majority of uses. 

The CAH has been developed to provide standard groupings that can be applied to both HECoS and JACS subjects allowing for consistent analysis across both coding frames. 

These aggregations provide some continuity in subject analysis through the transition from JACS to the HECoS and to other schemes such as those used by QAA. This will improve consistency across the sector.  Whereas the CAH has been designed to act as a bridge between HECoS and JACS, these are, however, two distinct coding frames, with HECoS having been developed in part to allow for more robust coding to address inconsistencies in coding using the JACS framework, and to remove limitations imposed by the JACS structure. As such, analysis between HECoS and JACS using this Common Aggregation Hierarchy will only provide indicative comparisons for time series analysis.

CAH Contents

The CAH is a comprehensive aggregation of the entirety of HECoS at each of three hierarchical levels or tiers, where a “parent” group at a higher level of CAH always comprises the full set of HECoS codes represented by related “child” groups of CAH below it. 

CAH groups are numbered with a series of two-digit integers representing a group of HECoS codes at a level, with the code at each level separated by a dash. Each unique CAH group code is referred to as a node. 

CAH tier

Node coding format (where nn is a 2-digit integer)

1

CAHnn

2

CAHnn-nn

3

CAHnn-nn-nn

Each node also has a label which serves to represent groups of subjects intelligibly and with rigour. Subject groupings (represented as nodes in the CAH) are not the same as subjects (represented by HECoS codes) even in cases where a CAH label is identical with a HECoS term. 

Where a higher-tier node is the parent of a single node at the next lower tier, they must share a title. 

Where a higher-tier node is the parent of more than one node at the next lower tier, they may not share the same title. 

In version 1.2 of the CAH, level 1 comprises 23 groups; level 2 comprises 35 groups, and; level 3 comprises 167 groups. 

In version 1.3.4 of the CAH, level 1 comprises 21 groups; level 2 comprises 35 groups; level 3 comprises 167 groups. 

Development of the CAH is subject to rules in the HECoS and CAH Management Guide (that can be found on the HECoS archive webpage).  In summer 2018 further research undertaken by the OfS (and DfE) identified areas where intended users of the CAH found groupings to be confusing, and as a result developed a proposal for amending the CAH. HESA worked closely with users of the CAH and Version 1.3 was created and approved by the Data Landscape Steering Group. To view changes between versions of CAH please view change log files that can be found under 'Download the CAH' section.

Version 1.2 of the CAH has been deprecated as from 31st July 2021.  

HESA continues to work with public bodies that are using CAH to support their work to support continued use of CAH for student funding and security. 

The following .csv files are published to detail version 1.3.4 of the CAH framework. 

Previous versions of the CAH framework (Versions 1.2 and 1.3) can be found under the 'Previous CAH Versions' section of the HECoS Archive webpage.

Please note that for ease of machine readability and ingestion of this data into other databases or systems and in line with HESA’s commitment to open data principles these files are provided in CSV format. 

When opening these files directly in Excel it maybe that Excel automatically convert some data into an inappropriate data type. For example, Excel may render CAH codes in the format 01-02-03 as a date.  If this issue is experienced, download the file to a local folder then, rather than opening the CSV file in Excel via File | Open, use the data import function, taking care to select the data type of ‘text’ for the relevant columns.

CAH groupings CSV File

CAH groupings (No Labels) CSV File

HECoS to CAH mapping CSV File

HECoS to CAH mapping (No Labels) CSV File

A simplified presentation of the current release of the CAH is also available, showing the relationship between the nodes 

CAH Level 1 CAH Level 2 CAH Level 3
(CAH01)
medicine and dentistry
(CAH01-01)
medicine and dentistry
(CAH01-01-01)
medical sciences (non-specific)
(CAH01-01-02)
medicine (non-specific)
(CAH01-01-03)
medicine by specialism
(CAH01-01-04)
dentistry
(CAH02)
subjects allied to medicine
(CAH02-02)
pharmacology, toxicology and pharmacy
(CAH02-02-01)
pharmacology
(CAH02-02-02)
toxicology
(CAH02-02-03)
pharmacy
(CAH02-04)
nursing and midwifery
(CAH02-04-01)
nursing (non-specific)
(CAH02-04-02)
adult nursing
(CAH02-04-03)
community nursing
(CAH02-04-04)
midwifery
(CAH02-04-05)
children's nursing
(CAH02-04-06)
dental nursing
(CAH02-04-07)
mental health nursing
(CAH02-04-08)
learning disabilities nursing
(CAH02-04-09)
others in nursing
(CAH02-05)
medical sciences
(CAH02-05-01)
medical technology
(CAH02-05-02)
healthcare science (non-specific)
(CAH02-05-03)
biomedical sciences (non-specific)
(CAH02-05-04)
anatomy, physiology and pathology
(CAH02-06)
allied health
(CAH02-06-01)
health sciences (non-specific)
(CAH02-06-02)
nutrition and dietetics
(CAH02-06-03)
ophthalmics
(CAH02-06-04)
environmental and public health
(CAH02-06-05)
physiotherapy
(CAH02-06-06)
complementary and alternative medicine
(CAH02-06-07)
counselling, psychotherapy and occupational therapy
(CAH03)
biological and sport sciences
(CAH03-01)
biosciences
(CAH03-01-01)
biosciences (non-specific)
(CAH03-01-02)
biology (non-specific)
(CAH03-01-03)
ecology and environmental biology
(CAH03-01-04)
microbiology and cell science
(CAH03-01-05)
plant sciences
(CAH03-01-06)
zoology
(CAH03-01-07)
genetics
(CAH03-01-08)
molecular biology, biophysics and biochemistry
(CAH03-01-09)
hair and beauty sciences
(CAH03-01-10)
others in biosciences
(CAH03-02)
sport and exercise sciences
(CAH03-02-01)
sport and exercise sciences
(CAH04)
psychology
(CAH04-01)
psychology
(CAH04-01-01)
psychology (non-specific)
(CAH04-01-02)
applied psychology
(CAH04-01-03)
developmental psychology
(CAH04-01-04)
psychology and health
(CAH04-01-05)
others in psychology
(CAH05)
veterinary sciences
(CAH05-01)
veterinary sciences
(CAH05-01-01)
veterinary medicine and dentistry
(CAH05-01-02)
others in veterinary sciences
(CAH06)
agriculture, food and related studies
(CAH06-01)
agriculture, food and related studies
(CAH06-01-01)
animal science
(CAH06-01-02)
agricultural sciences
(CAH06-01-03)
agriculture
(CAH06-01-04)
rural estate management
(CAH06-01-05)
forestry and arboriculture
(CAH06-01-06)
food and beverage studies (non-specific)
(CAH06-01-07)
food sciences
(CAH06-01-08)
food and beverage production
(CAH07)
physical sciences
(CAH07-01)
physics and astronomy
(CAH07-01-01)
physics
(CAH07-01-02)
astronomy
(CAH07-02)
chemistry
(CAH07-02-01)
chemistry
(CAH07-04)
general, applied and forensic sciences
(CAH07-04-01)
physical sciences (non-specific)
(CAH07-04-02)
forensic and archaeological sciences
(CAH07-04-03)
sciences (non-specific)
(CAH07-04-04)
natural sciences (non-specific)
(CAH09)
mathematical sciences
(CAH09-01)
mathematical sciences
(CAH09-01-01)
mathematics
(CAH09-01-02)
operational research
(CAH09-01-03)
statistics
(CAH10)
engineering and technology
(CAH10-01)
engineering
(CAH10-01-01)
engineering (non-specific)
(CAH10-01-02)
mechanical engineering
(CAH10-01-03)
production and manufacturing engineering
(CAH10-01-04)
aeronautical and aerospace engineering
(CAH10-01-05)
naval architecture
(CAH10-01-06)
bioengineering, medical and biomedical engineering
(CAH10-01-07)
civil engineering
(CAH10-01-08)
electrical and electronic engineering
(CAH10-01-09)
chemical, process and energy engineering
(CAH10-01-10)
others in engineering
(CAH10-03)
materials and technology
(CAH10-03-01)
minerals technology
(CAH10-03-02)
materials technology
(CAH10-03-03)
polymers and textiles
(CAH10-03-04)
maritime technology
(CAH10-03-05)
biotechnology
(CAH10-03-06)
others in technology
(CAH10-03-07)
materials science
(CAH11)
computing
(CAH11-01)
computing
(CAH11-01-01)
computer science
(CAH11-01-02)
information technology
(CAH11-01-03)
information systems
(CAH11-01-04)
software engineering
(CAH11-01-05)
artificial intelligence
(CAH11-01-06)
computer games and animation
(CAH11-01-07)
business computing
(CAH11-01-08)
others in computing
(CAH13)
architecture, building and planning
(CAH13-01)
architecture, building and planning
(CAH13-01-01)
architecture
(CAH13-01-02)
building
(CAH13-01-03)
landscape design
(CAH13-01-04)
planning (urban, rural and regional)
(CAH15)
social sciences
(CAH15-01)
sociology, social policy and anthropology
(CAH15-01-01)
social sciences (non-specific)
(CAH15-01-02)
sociology
(CAH15-01-03)
social policy
(CAH15-01-04)
anthropology
(CAH15-01-05)
development studies
(CAH15-01-06)
cultural studies
(CAH15-02)
economics
(CAH15-02-01)
economics
(CAH15-03)
politics
(CAH15-03-01)
politics
(CAH15-04)
health and social care
(CAH15-04-01)
social work
(CAH15-04-02)
childhood and youth studies
(CAH15-04-03)
health studies
(CAH16)
law
(CAH16-01)
law
(CAH16-01-01)
law
(CAH17)
business and management
(CAH17-01)
business and management
(CAH17-01-01)
business and management (non-specific)
(CAH17-01-02)
business studies
(CAH17-01-03)
marketing
(CAH17-01-04)
management studies
(CAH17-01-05)
human resource management
(CAH17-01-06)
tourism, transport and travel
(CAH17-01-07)
finance
(CAH17-01-08)
accounting
(CAH17-01-09)
others in business and management
(CAH19)
language and area studies
(CAH19-01)
English studies
(CAH19-01-01)
English studies (non-specific)
(CAH19-01-02)
English language
(CAH19-01-03)
literature in English
(CAH19-01-04)
studies of specific authors
(CAH19-01-05)
creative writing
(CAH19-01-06)
others in English studies
(CAH19-01-07)
linguistics
(CAH19-02)
Celtic studies
(CAH19-02-01)
Celtic studies (non-specific)
(CAH19-02-02)
Gaelic studies
(CAH19-02-03)
Welsh studies
(CAH19-02-04)
others in Celtic studies
(CAH19-04)
languages and area studies
(CAH19-04-01)
French studies
(CAH19-04-02)
German and Scandinavian studies
(CAH19-04-03)
Italian studies
(CAH19-04-04)
Iberian studies
(CAH19-04-05)
Slavic studies
(CAH19-04-06)
Asian studies
(CAH19-04-07)
African and modern Middle Eastern studies
(CAH19-04-08)
American and Australasian studies
(CAH19-04-09)
others in language and area studies
(CAH20)
historical, philosophical and religious studies
(CAH20-01)
history and archaeology
(CAH20-01-01)
history
(CAH20-01-02)
history of art, architecture and design
(CAH20-01-03)
archaeology
(CAH20-01-04)
heritage studies
(CAH20-01-05)
classics
(CAH20-02)
philosophy and religious studies
(CAH20-02-01)
philosophy
(CAH20-02-02)
theology and religious studies
(CAH22)
education and teaching
(CAH22-01)
education and teaching
(CAH22-01-01)
education
(CAH22-01-02)
teacher training
(CAH23)
combined and general studies
(CAH23-01)
combined and general studies
(CAH23-01-01)
combined, general or negotiated studies
(CAH23-01-02)
personal development
(CAH23-01-03)
humanities (non-specific)
(CAH23-01-04)
liberal arts (non-specific)
(CAH24)
media, journalism and communications
(CAH24-01)
media, journalism and communications
(CAH24-01-01)
information services
(CAH24-01-02)
publicity studies
(CAH24-01-03)
publishing
(CAH24-01-04)
journalism
(CAH24-01-05)
media studies
(CAH25)
design, and creative and performing arts
(CAH25-01)
creative arts and design
(CAH25-01-01)
creative arts and design (non-specific)
(CAH25-01-02)
art
(CAH25-01-03)
design studies
(CAH25-01-04)
cinematics and photography
(CAH25-01-05)
others in creative arts and design
(CAH25-02)
performing arts
(CAH25-02-01)
performing arts (non-specific)
(CAH25-02-02)
music
(CAH25-02-03)
drama
(CAH25-02-04)
dance
(CAH26)
geography, earth and environmental studies
(CAH26-01)
geography, earth and environmental studies
(CAH26-01-01)
geography (non-specific)
(CAH26-01-02)
physical geographical sciences
(CAH26-01-03)
human geography
(CAH26-01-04)
environmental sciences
(CAH26-01-05)
others in geographical studies
(CAH26-01-06)
earth sciences

Changes between versions of the CAH

To assist users of the CAH to understand the differences between versions a change log has been produced.

CAH Change Log CSV File

CAH & HECoS Change Log CSV File

In preparation for the release of the HESA 2019/20 Student Statistical Bulletin, HESA investigated the quality characteristics of the CAH. 2019/20 data was compared with data from 2018/19. HESA derived the CAH groups for each dataset, to look at changes in how students were distributed in each year. Preliminary analysis revealed that a small overall average change in the distribution of students masks wider underlying variations. Many individual CAH level 1 and CAH level 3 groups show more substantial changes in the numbers of students allocated to them. These differences appear to reflect underlying changes to courses, as well as movement from the many ‘others in…’ categories within JACS to the precisely defined subjects in HECoS. HESA  determined that these inconsistencies meant it should not use CAH v1.2 for presentation of its initial outputs containing time series.

CAH to HECoS Mapping

Use this search function to view HECoS Subject Codes mapped a CAH Code.

A .csv file containing all CAH to HECoS mappings is availible under the 'Download the CAH' section above.


Search results will show here