meri snowdon what’s all this mesh? an introduction to medical subject headings

Meri Snowdon

What’s all this MeSH?

An introduction toMedical Subject Headings

www.bradfordvts.co.uk

Meri Snowdon

From the guru of EBM -

‘MEDLINE is the best general source of current best evidence at present because of its breadth and constant maintenance. Thus, it is important to evidence-based practice that clinicians develop and hone MEDLINE searching skills and acquire local access.’

Evidence-based Medicine: how to practice & teach EBM - Sackett D L et al 1998

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Medline

Library (Ovid windows) Hospital network (Knowledge

Finder) BMA (Ovid web) PubMed (web) Internet Grateful Med (web) Other (Silver Platter, Dialog .....)

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Three great lies ...

The cheque is in the post

Of course I’ll still respect you in the morning

MeSH is exciting

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MeSH

Removes the uncertainty– Have I thought of all the synonyms?– Have I tried all the spellings?– Have I included all the variants?– Did the author use my term(s) at all?

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Playing the game

The indexers set the rules - you have to play by them!

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From broad to specific

Start off by being inclusive - keep it broad

THEN narrow it down by using limits

Narrowing too soon will make you miss things

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The tree structure

Respiratory tract diseases– Bronchial Diseases

Asthma– Asthma, Exercise-Induced– Status Asthmaticus

– Ciliary Motility Disorders ....................

– Laryngeal Diseases ......................

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No misspelt MeSH

MeSH terms are never misspelt as they are entered automatically not manually

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The most specific term

Intestinal neoplasms 591– Cecal neoplasms 136– Colonic neoplasms 4929– Duodenal neoplasms 385– Ileal neoplasms 227– Intestinal polyps 260– Jejunal neoplasms 189– Rectal neoplasms 2189

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Exploding

Bronchial Diseases– Asthma

Asthma, Exercise-Induced

Status Asthmaticus

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Difficult asthma (a letter)*Asthma/px [Psychology]Asthma/th [Therapy]ChildHumanPractice GuidelinesPsychology, Social

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Focus (& textwords)

1 *asthma 75172 asthma/ 91083 asthma.tw. 97954 1 not 3 10005 2 not 3 17806 3 not 2 2467

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Friedrich Wilhelm I and porphyria

‘The diagnosis of porphyria was not recognized then and other names were used such as ..... asthma spasmodica flatulentum .....’

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Subheadings for Asthma classification complications diagnosis epidemiology prevention & control psychology surgery ...........................

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Exploding subheadings

Therapeutic use tu.xs.

– administration & dosage

– adverse effects– contraindications– poisoning

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Exploding subheadings

Diagnosis di.xs

– pathology– radiography– radionuclide

imaging– ultrasonography

Pharmacology ph.xs.

– admin & dosage– adverse effects– contraindications– diagnostic use– pharmakinetics– poisoning– toxicity

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Combining

1 *self-help groups 4452 support groups.tw. 2573 *asthma 77084 1 or 2 6155 3 and 4 66 self-help groups/ 7987 6 and 3 68 7 not 5 2

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OR is MORE

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Limits

Local holdings (for library only) Age groups Publication types Language Year of publication Human/animal etc

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Still too much?

Use the most specific subject headings

Use focus Use subheadings Use AND Use limits Restrict textword searching to title

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Or too little?

Use OR Use explode Use All Subheadings Don’t use focus Consider synonyms, alternative

spellings or truncation

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And always remember

Check the MeSH headings used for the most relevant articles and add them to your search if necessary.

You cannot find what is not there!

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Sensitivity and Specificity If a search is too

sensitive, it will retrieve too much irrelevant material

If a search is too specific, it will miss relevant material

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WHY are you searching? Do you want one

decent article on a topic?

Do you need evidence?

Are you writing a letter/book/article/systematic review?

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WHAT are you looking for?

Systematic reviews

Clinical trials Traditional reviews Guidelines General

information Letters

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Look in the right place

Full-text systematic reviews - on CL All Medline clinical trials + others are

in Cochrane Controlled Trials Register Cochrane looks only at

EFFECTIVENESS Medline includes a very wide range of

publications & can answer a wide range of questions

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The right place to look

Cochrane Library for effectiveness questions - diagnosis, prognosis, treatment

Medline for other questions - general information, epidemiology, aetiology, surgical techniques etc

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MeSH on Cochrane Library Many items on the CL are indexed

with MeSH terms BUT not all of them are SO the offical recommendation is

to use MeSH and textword searching combined

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Text word searching

Looks for exact matchesDoesn’t allow for

– variants - pregnancy, pregnant, pregnancies– alternative spellings - diarrhoea, diarrhea– synonyms - preterm birth, premature birth;

cancer, neoplasm

Apart from Knowledge Finder which uses fuzzy logic

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FieldsThe different parts of each item on a database are called fields, and most can be searched individually. In Ovid

– ti = title– au = author– ab = abstract– tw = textword (title or abstract)– in = institution– pg = page

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What you miss

oral thrush 27 candidiasis, oral/ 412

breast cancer 13879 breast neoplasms/ 18754

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What you miss??

heart attack 236 myocardial infarction 11040

myocardial infarction/ 10091

= 949 irrelevant articles - at least!!

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Stop words

Many common, normally insignificant, words are ignored in free text searching. This can be a problem when looking for concepts such as ‘out-of-hours’ or ‘after-hours’. There is no way round this unless there is a relevant subheading. In this case there isn’t!!

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Hyphens

Different systems treat these in different ways. They may be ignored or treated as spaces or treated as hyphens.

To be safe try all options eg– postnatal– post natal– post-natal

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Mizspellins

Ray & Vermeulen found a total of 200 instances of 10 misspelt textwords in Medline between 1966 and 1996.

Ray J G & Vermeulen M JBMJ 1996 313:1658-9

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1996-1999

antibotics 4 asprin 1 dopler 2 cholestrol 1 thrombolism 3 myocardial infraction 34

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haemorrhage??

hamorrhage 1 haemorhage 3 hemorhage 1

and no doubt there’s more!!

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Truncation

This can be used to overcome some of the problems of free text searching. Different wild cards are used by different systems. Mainly * $ and ?

Can be used at the end of a word for truncation eg pregnan$ or in the middle for spelling variants eg wom?n, an?emia

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Textword advantages

New concepts eg new drugs British concepts eg clinical

governance, Project 2000 Tradenames

MeSH headings are updated annually

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Further reading

Sackett D L et al - Evidence-based medicine: how to practice & teach EBM. Churchill Livingstone, 1998

Roberts R - Information for evidence-based care. Radcliffe, 1999

Chambers R - Clinical effectiveness made easy. Radcliffe, 1998