Revising Subheadings

As medical librarians know well, achieving precision in retrieval over a
large literature database requires the use of a controlled vocabulary. A
vocabulary must represent the content in a single, unique way. Achieving
this representational integrity allows users to be confident that they
are retrieving materials which are relevant to their query. At the same
time, it is desirable that recall, or the appearance of relevant
articles in the retrieval set, be high. It does a user no service to
fail to retrieve a substantial number of the important relevant
articles. The subheadings in MeSH have long been used to help indicate
the content of articles. When developed and used properly, they can be a
valuable addition in the MEDLINE database. However, for the reasons
discussed below, NLM is undertaking a review of subheadings and has
developed a proposal for revising them.

A controlled vocabulary should adhere to a standard of good practices.
Understandability, Reproducibility and Usability (URU) is one such set
of quality criteria. Understandability requires that users of the
terminology fully and unambiguously comprehend a concept or term.
Reproducibility requires that multiple users will apply the concept to
the same situations in the same way. Usefulness measures the helpfulness
and appropriateness conveyed in a concept or feature. These criteria
apply to the entire set of vocabulary terms taken as a whole as well as
to each individual term.

The Medical Subject Headings (MeSH) vocabulary currently includes 83
subheadings. Also known as qualifiers, they refine or segment literature
associated with specific MeSH descriptors. Introduced with the first
edition of MeSH in 1960, these were originally developed to assist those
using the former printed *Index Medicus, NLM Catalog*, and other printed
bibliographic tools. Specifically, the qualifiers provided logical
divisions or breakdowns of citations on printed pages.

As first described, "subheadings are to be understood as shorthand for
large concepts." MeSH began with 39. Of the original 39, four
represented population groups (age groups and pregnant females). Two
represented publication types: "bibliography" and "case reports". Out of
the original list, there were 33 subheadings as we know them today.

The user looking at the printed *Index Medicus* could immediately see
the various choices of qualifiers and browse the sections of likely
interest. That kind of browsing and serendipitous retrieval is not the
hallmark of an online system. The typical user of *Index Medicus* was in
a healthcare environment. The typical user was most likely a healthcare
professional as the average medical library did not serve patients or
the public. Today there is no printed version of MEDLINE, no *Index
Medicus*. The users of MEDLINE data are diverse, are from different
backgrounds, and are not a finite audience which can be trained and
instructed.

Qualifiers have been defined more narrowly over time with greater and
greater specificity. For example, *anatomy & histology* spawned
*cytology*, and *ultrastructure*. In some cases, the added qualifiers,
intended for a specific use to reduce ambiguity, have been a potential
source of confusion to both indexers and searchers. As a result, the
proliferation of subheadings has led to a complexity which taxes the
reproducibility criteria for good vocabulary.

A recent NLM study of indexing consistency showed that the qualifiers
were applied with greater than 50% variation between individual indexers
in the study. This particular aspect of indexing was the least
consistent. That is to say, the likelihood of a relevant qualifier being
applied consistently from one indexer to another was less than 50%. Funk
and Reid in 1983 reported similar results in their earlier study.

The principle of coordinating main headings and qualifiers is a
difficult aspect to teach and to apply consistently. The naïve user will
not know that if the subject matter of an article is covered by three or
more qualifiers, then the most broad is applied and not the specifics.
Those without sophisticated medical knowledge may not know the
difference between *anatomy, cytology*, and *ultrastructure* and that
the boundaries of meaning are set by the technology used and decreasing
size of the object under study.

The following example shows the precise description that MeSH provides
but also reveals how daunting for the unaware:

What is the best schedule for administration of gemcitabine-taxane?

Cancer Treat Rev. 2005;31 Suppl 4:S23-8.

MH - Antibodies, Monoclonal/[administration & dosage]{.underline}

MH - Antimetabolites, Antineoplastic/\*[administration &
dosage]{.underline}

MH - Antineoplastic Agents/[administration & dosage]{.underline}

MH - Antineoplastic Agents, Phytogenic/\*[administration &
dosage]{.underline}

MH - Antineoplastic Combined Chemotherapy Protocols[/\*therapeutic
use]{.underline}

MH - Breast Neoplasms/\*[drug therapy]{.underline}

MH - Bridged Compounds/\*[administration & dosage]{.underline}

MH - Deoxycytidine/[administration & dosage/\*analogs &
derivatives]{.underline}

MH - Drug Administration Schedule

MH - Drug Synergism

MH - Female

MH - Humans

MH - Neoplasm Metastasis

MH - Paclitaxel/[administration & dosage]{.underline}

MH - Receptor, erbB-2[/antagonists & inhibitors]{.underline}

MH - Remission Induction

MH - Taxoids/[\*administration & dosage]{.underline}

How effectively qualifiers can be used in a search depends a great deal
upon the sophistication and abilities of the searcher. Unfortunately,
the lack of consistency in assignment of qualifiers results in poor
recall even in well constructed searches. The citations that are
retrieved are likely to be highly relevant, but equally relevant
citations will not be retrieved. As a result, some sophisticated
information access providers have concluded that some types of searches
with the existing qualifiers need to be combined, broadening the
retrieval to improve recall.

Derry, Loke and Aronson claimed that indexing terms for adverse effects
in the MEDLINE database were generally assigned only to papers in which
the author devoted substantive discussion to the adverse effects. They
found that about 23% of papers containing adverse effects data did not
have text words or indexing terms identifying the data as relating to
adverse effects, and would therefore be missed by electronic searches.
\[BMC Medical Research Methodology 2001, 1:7\]

Golder, McIntosh, Duffy and Glanville applied five approaches to
searching for adverse effects evidence. The sensitivity and precision of
these five approaches, and combinations of these approaches, were
compared in a case study using a systematic review of the adverse
effects of seven anti-epileptic drugs. Recall was less than 50%, with a
low precision as well. \[Health Info Libr J. 2006 Mar;23(1):3-12\]

  ------------------------------------------------------------ -------------- ---------- ------------- -----------
  Approach 2a: Subheadings linked to MeSH indexing term                                                
  VIGABATRIN[\*](javascript:popRef('t2n5','citart0','2',''))                                           
  (QGS = 29)                                                                                           

                                                               \# records     \#         sensitivity   precision
                                                               retrieved      relevant                 

    VIGABATRIN/ae, po, to                                        99           12         41.4%         12.1%

    VIGABATRIN/ae                                                99           12         41.4%         12.1%

    VIGABATRIN/to                                                 1            1          3.4%          100%

    VIGABATRIN/po                                                 1            0            0%            0%
  ------------------------------------------------------------ -------------- ---------- ------------- -----------

Over time some qualifiers have also been assigned special meanings in
MeSH which are not the same meanings generally assigned to the same
expressions. The current MeSH definition of *abnormalities* is
"congenital defects producing changes in the morphology of the organ."
Random House Unabridged Dictionary gives "an abnormal condition, state,
irregularity". The meaning in MeSH is very narrowly defined, and is
likely to mislead most users. A similar situation is true of
*complications*. The MeSH definition, "conditions that co-exist or
follow, i.e., co-existing disease, complications, or sequelae", covers
only part of the usual meaning. The broader meaning, for undesired
results from surgical or medical procedures or drugs and other
treatments, is ignored. The following indexed titles from PubMed are
[not]{.underline} indexed with *complications* (correctly), yet the
titles suggest a PubMed searcher seeking articles on untoward outcomes
might expect them to be indexed with that qualifier:

-   Combined-modality therapy versus radiotherapy alone for treatment of
    early-stage Hodgkin\'s disease: cure balanced against complications.

-   Neurological complications following Haematopoiesis stem cell
    transplantation. Study of 14 patients

-   Neurologic and psychiatric complications of antiretroviral agents.

-   Organ transplantation: cutaneous complications

-   Complications of decubitus immobilization. Prevention and
    management: decubitus ulcer\]

Similar problems with special meaning also apply to the qualifiers for
*blood*, *urine*, *chemistry*, *cerebrospinal fluid*, among others. A
simple redefinition of the existing qualifiers would not correct the
allocation of subheadings to MEDLINE citations over the last four
decades. Combining closely-related qualifiers into broader and more
comprehensible concept groups addresses both needs.

NLM has undertaken a review of the existing 83 topical qualifiers and
has created a plan to reduce these to 40. With the exception of
*education*, which would be combined with the Main Heading of Education,
deleted qualifiers will be retained within somewhat broader qualifiers
as entry terms or subordinate concepts. Terms from the existing
qualifiers will be retained. Preservation of the entry vocabulary for
each qualifier will insure that no access points will be lost. There
will be less uncertainly regarding which qualifier to use and MeSH will
have restored the remaining qualifiers to their original purpose, as
shorthand for broad or overarching concepts.

Simplification will make searching easier and more straightforward for
those who use qualifiers in searching. For those who apply qualifiers in
indexing, cataloging and subject analysis, the streamlined qualifier
array provides ease of use, with consistency and efficiency. With the
retention of all access points, users will be able to continue to use
the terminology with which they are familiar. Those taking advantage of
PubMed's hierarchical retrieval feature, will notice little or no change
to searching or retrieval. Others will find that there is a simpler list
of qualifiers to select among with greater likelihood of desired
results. First-time or infrequent users will have more likelihood of
successful retrieval.

The proposed changes retain familiar broad groups. For example, the
qualifier *adverse effects* will include *poisoning* and *toxicity* as
subordinate concepts while the qualifier *anatomy* will include the
subordinate concepts of *blood supply, cytology, embryology,
innervation*, and *ultrastructure*. The following array shows the
proposed list of qualifiers arranged hierarchically. The array also
shows retained qualifiers with proposed subordinate concept groupings.

Comments are sought on the proposed changes. Comments should address the
goals of Understandability, Reproducibility and Usability and may be
sent to Stuart J. Nelson, MD, Head, MeSH Section, NLM
\[nelsonst@mail.nih.gov\] by April 14, 2006.

**Revised MeSH Qualifier Concepts and Hierarchy (**04/13/06)

**bold** = retained qualifier *italics* = deleted qualifier which
becomes an entry term [underline]{.underline} = maintained to MH

**adverse effects**

*poisoning*

*toxicity*

**anatomy**

*blood supply*

*cytology*

*embryology*

*innervation*

*ultrastructure*

**analysis**

*analogs & derivatives*

*blood*

*cerebrospinal fluid*

*chemistry*

*chemical synthesis*

*isolation & purification*

*urine*

**classification**

**diagnosis**

**diagnostic imaging**

*radiography*

*radionuclide imaging*

*ultrasonography*

**economics**

[education -- to become Education \[NIM\]]{.underline}

**epidemiology**

*mortality*

**ethics**

**ethnology**

**etiology**

*complications*

*secondary*

*transmission*

**chemically induced**

**congenital**

**deficiency**

**genetics**

**immunology**

**microbiology**

*parasitology*

*pathogenicity*

*virology*

**history**

**injuries**

**legislation & jurisprudence**

**methods**

*instrumentation*

**organization & administration**

*manpower*

*standards*

*supply & distribution*

**pathology**

*abnormalities*

*physiopathology*

**pharmacology**

**antagonists & inhibitors**

*administration & dosage*

*agonists*

*diagnostic use*

*drug effects*

*pharmacokinetics*

**therapeutic use**

*contraindications*

**physiology**

*enzymology*

*growth & development*

**genetics**

**immunology**

**metabolism**

*biosynthesis*

**secretion**

**psychology**

**radiation effects**

**statistics & numerical data**

*trends*

*utilization*

**therapy**

*diet therapy*

**drug therapy**

**nursing**

**prevention & control**

**radiotherapy**

**rehabilitation**

**surgery**

*transplantation*

**veterinary**

**Alphabetic List of Proposed Deletes with Mapping**

abnormalities = /pathology

administration & dosage = /pharmacology

agonists = /pharmacology

analogs & derivatives = /analysis

biosynthesis = /metabolism

blood = /analysis

blood supply = /anatomy

cerebrospinal fluid = /analysis

chemical synthesis = /analysis

chemistry = /analysis

complications = /etiology

congenital = /etiology

contraindications = /therapeutic use

cytology = /anatomy

deficiency = /etiology

diagnostic use = /pharmacology

diet therapy = /therapy

drug effects = /pharmacology

education = Education

embryology = /anatomy

enzymology = /physiology

growth & development = /physiology

innervation = /anatomy

instrumentation = /methods

isolation & purification = /analysis

manpower = /organization & administration

mortality = /epidemiology

parasitology = /microbiology

pathogenicity = /microbiology

pharmacokinetics = /pharmacology

physiopathology = /pathology

poisoning = /adverse effects

radiography = /diagnostic Imaging

radionuclide imaging = /diagnostic Imaging

secondary = /etiology

standards = /organization & administration

supply & distribution = /organization & administration

toxicity = /adverse effects

transmission = /etiology

transplantation = /surgery

trends = /statistics & numerical data

ultrasonography = /diagnostic Imaging

ultrastructure = /anatomy

urine = /analysis

utilization = /statistics & numerical data

virology = /microbiology

**Alphabetic List of All Qualifiers**

**bold** = retained qualifier *italics* = deleted qualifier which
becomes an entry term [underline]{.underline} = maintained to MH

*administration & dosage*

**adverse effects**

*agonists*

*analogs & derivatives*

**analysis**

**anatomy**

**antagonists & inhibitors**

*biosynthesis*

*blood*

*blood supply*

*cerebrospinal fluid*

*chemical synthesis*

**chemically induced**

*chemistry*

**classification**

*complications*

**congenital**

*contraindications*

*cytology*

**deficiency**

**diagnosis**

**diagnostic imaging** (new 2007)

*diagnostic use*

*diet therapy*

*drug effects*

**drug therapy**

**economics**

[education -- to become Education \[NIM\]]{.underline}

*embryology*

*enzymology*

**epidemiology**

**ethics**

**ethnology**

**etiology**

**genetics**

**genetics**

*growth & development*

**history**

**immunology**

**immunology**

**injuries**

*innervation*

*instrumentation*

*isolation & purification*

**legislation & jurisprudence**

*manpower*

**metabolism**

**methods**

**microbiology**

*mortality*

**nursing**

**organization & administration**

*parasitology*

*pathogenicity*

**pathology**

*pharmacokinetics*

**pharmacology**

**physiology**

*physiopathology*

*poisoning*

**prevention & control**

**psychology**

**radiation effects**

*radiography*

*radionuclide imaging*

**radiotherapy**

**rehabilitation**

*secondary*

**secretion**

*standards*

**statistics & numerical data**

*supply & distribution*

**surgery**

**therapeutic use**

**therapy**

*toxicity*

*transmission*

*transplantation*

*trends*

*ultrasonography*

*ultrastructure*

*urine*

*utilization*

**veterinary**

*virology*