Health Evidence Bulletins - Wales


The original series Protocols for Investment in Health Gain were written in the early 1990s to suggest areas where the introduction, or more widespread use, of certain practices could lead to worthwhile improvements in health for the people of Wales. This revision has been prepared by reviewing the earlier Protocol for Investment in Health Gain: Learning Disabilities to provide some clear, updated statements with a precise indication of the strength of the evidence and its sources for each statement. The bulletin also introduces new statements covering recent developments and subjects of important current interest.

The statements represent a methodical summary of the evidence in this area found through a formal literature search across a wide range of sources2. The evidence has been critically appraised using internationally accepted methods2, compiled into this document under the direction of a public health physician, and reviewed by a multidisciplinary team who are directly involved in patient care. The information in this document will also be available electronically, via the NHS Cymruweb (http://nww.wales.nhs.uk/hebw) and the Internet (http://hebw.cardiff.ac.uk). Information on the methodology adopted (including a copy of the documentation), the formats in which the document is issued and details of other publications in the series are available on request.


The convention used in this document to indicate the type of evidence is:

‘Type I evidence’ - at least one good systematic review and meta-analysis
(including at least one randomised controlled trial).
‘Type II evidence’ - at least one good randomised controlled trial
‘Type III evidence’ - well designed interventional studies without randomisation
‘Type IV evidence’ - well designed observational studies
‘Type V evidence’ - expert opinion; influential reports and studies

Many health issues and interventions in the field of intellectual disability do not lend themselves to investigation by randomised controlled trial. Much of the quoted evidence is Type III, IV and V. There were very few randomised controlled trials to be found in the literature and even fewer systematic reviews. By valuing evidence from randomised controlled trials more highly than observational studies there is a danger that interventions with limited effectiveness might be judged to be more worthy than those based on observation. Similarly, those observational studies which clearly prove effectiveness (and make a randomised trial unethical) might be undervalued. Information assigned as Type V evidence may include expert opinion and important reports or recommendations which should rightly be highly regarded.


The health gain notation (used to indicate the potential benefit to health) is:

(1) ‘beneficial’ - effectiveness clearly demonstrated
(2) ‘likely to be beneficial’ - effectiveness not so firmly established
(3) ‘trade-off between beneficial and adverse effects’ - effects weighed according to individual circumstances
(4) ‘unknown’ - insufficient/inadequate for recommendation
(5 ‘unlikely to be beneficial’ - ineffectiveness is not as clearly demonstrated as for (6)
(6) ‘likely to be ineffective or harmful’ - ineffectiveness or harm clearly demonstrated

It should be stressed that these gradings, while aiming to be impartial, represent only the best advice of the professionals involved in preparing the Bulletin. Where possible the health gain notation reflects both the type of evidence and the small size of some of the samples. Although the statements are deliberately brief, statistically significant quantitative information has been provided where possible. Issues of cost-effectiveness or cost-benefit are considered where evidence is available.

In keeping with the original Protocols, these revised documents are designed to assist Health Authorities in developing local strategies and in commissioning high quality health care. It is anticipated that they will also be of value to all professionals involved in delivering services for people with intellectual disability in keeping abreast of the large and increasing body of literature in this field. It should be stressed that the publications will act as a supplement to, not a substitute for, skills and experience. Some of the conclusions reached in this bulletin will inevitably be controversial. Every effort has been made to include the best evidence within a subject area. Readers who are aware of any important studies that have been overlooked are encouraged to contact the project team3.


The Learning Disabilities Health Evidence Bulletin

The prevalence rate in Western countries for moderate to severe intellectual disability is 30 per 1000 population. As such it is a common condition affecting at least 3% of the population and not surprisingly, people with intellectual disability have many of the conditions found in the general population. This bulletin therefore considers a number of medical conditions with a known association with intellectual disability. The areas covered in this bulletin include:

A deliberate decision has been taken to leave out a number of areas from the bulletin due to difficulties either in identifying adequate literature in those areas or because the area has been covered in detail in another protocol. Areas omitted include ethics, medical conditions (other than epilepsy, thyroid disease and mental illness) and communication and special education in adults. Carers and caring is covered in great detail in the Healthy Living Bulletin and cardiovascular disease is reviewed in the cardiovascular diseases Bulletin.


There is continuing confusion and complexity surrounding the classification of intellectual disability. With little agreement on terms, there is clearly a need for agreeing a common terminology. There are a range of general titles used in public phraseology depending upon local fashion, public confusion and prejudice, issues of perceived stigma, offensiveness and correctness. In this bulletin we have used the term ‘Intellectual Disability’ except where another term is used as part of a formal reference. Terms include:

Some authors propose a more innovative exploration of the potential of the multi-dimensional framework of the ICIDH-210. The current ICD-10 classification is limited, based upon assessment of IQ and an additional fourth character to identify the extent of impairment of behaviour11:

The statements made in this bulletin present a graded summary of the best available evidence of effectiveness across the spectrum of intellectual disability. The following information sources were systematically searched in the preparation of this Bulletin, according to the Project Methodology2: Cochrane Library, Medline, Pre-Medline, Embase, CINAHL, PsychINFO, ASSIA, Caredata, Rehabdata, National Research Register, Health Promis, the TRIP database, AMED, SIGLE. The full search strategies are available from the Project Office3. The date of completion of the literature search for each chapter is given. Some additional evidence, published since the date of the systematic literature search, has been added on the basis of recommendations by Authors and/or the Review Groups where this lends support to an existing statement. The statements are intended to act as signposts to further sources of evidence, not as guidelines for the management of patients. It is hoped that this bulletin will facilitate evidence-based practice, which involves "integrating individual expertise with the best available external evidence from systematic research".


Dr Laurence Hamilton-Kirkwood, Team Leader. December 2000.

  1. Welsh Health Planning Forum. Protocol for Investment in Health Gain – Learning Disabilities. Cardiff: Welsh Office NHS Directorate, August 1992.
  2. Weightman AL, Barker J, Lancaster J. Health Evidence Bulletins Wales. Project Methodology 3. Cardiff: University of Wales College of Medicine, 2000. http://hebw.cardiff.ac.uk/methodology/index.htm
  3. Contact: Health Evidence Bulletins Wales, Department of Information Services, UWCM, Cardiff CF14 4XN.
  4. This table is adapted from the Bandolier system (derived from the work at McMaster University, Canada) using the NHS Centre for Reviews and Dissemination criteria for a systematic review. See p.18 in ref.2 or http://www.jr2.ox.ac.uk/Bandolier/band6/b6-5.html [accessed 8.12.00] and the Database of Abstracts of Reviews of Effectiveness (DARE) in the Cochrane Library.
  5. This Notation is modified from the tables used in Enkin M, Keirse MJNC, Renfrew M and Neilson J. A Guide to Effective Care in Pregnancy and Childbirth. 2nd ed. Oxford: Oxford University Press, 1995 pp. 389-90.
  6. Roeleveld N, Zielhuis GA, Gabreels F. The prevalence of mental retardation: a critical review of recent literature. Developmental Medicine & Child Neurology. 1997: 39(2): 125-32.
  7. Health Evidence Bulletins Wales: Healthy Living. Cardiff: National Assembly for Wales, 2000. http://hebw.cardiff.ac.uk/healthyliving/index.html [accessed 8.12.00].
  8. Health Evidence Bulletins Wales: Cardiovascular Diseases. Cardiff: Welsh Office, 1998. http://hebw.cardiff.ac.uk/cardio/index.html [accessed 8.12.00]
  9. Fryers T. Epidemiology in relation to community and residential services. Current Opinion in Psychiatry. 1997: 10: 340-53.
  10. ICIDH-2: International Classification of Functioning and Disability. Beta-2 draft, Full Version. Geneva: World Health Organisation, July 1999
  11. ICD-10: International Classification of Diseases and Related Health Problems. 10th Revision. Geneva: World Health Organisation, 1992
  12. Sackett DL, Richardson WS, Rosenberg W, Haynes RB. Evidence-based Medicine. How to Practice and Teach EBM. Edinburgh: Churchill Livingstone, 1997.


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Health Evidence Bulletins: Wales, Duthie Library, UWCM, Cardiff CF14 4XN. e-mail: weightmanal@cardiff.ac.uk