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Healthy Environments Bulletin

The original 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. The documents also highlighted current practices which were of questionable value. This revision has been prepared by reviewing the earlier Protocol for Investment in Health Gain: Healthy Environments to provide some clear, updated statements with a precise indication of the strength of the evidence and its sources for each statement; and to introduce new statements covering 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 sources. 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 team of experts. In addition to this bulletin, the information is available in paper copy. 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, is 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 (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 do not lend themselves to investigation by randomised controlled trial. By valuing evidence from these 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. Observational studies must be used to study the aetiology of disease. Randomised controlled trials should then be carried out whenever feasible to assess the effectiveness of interventions. When available, results of randomised trials are included. If not, high quality evidence has been sought within the other categories. Information assigned as type V evidence includes very important reports or recommendations which should rightly be highly regarded.

The convention used to indicate the potential benefit to health is:

‘beneficial’ - effectiveness clearly demonstrated (1)

‘likely to be beneficial’ - effectiveness not so firmly established (2)

‘trade-off between beneficial and adverse effects’ - effects weighed according to individual circumstances(3)

‘unknown’ - insufficient/inadequate for recommendation (4)

‘unlikely to be beneficial’ - ineffectiveness is not as clearly demonstrated as for 6 (5)
‘likely to be ineffective or harmful’ - ineffectiveness or harm clearly demonstrated (6)

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. Although the statements are deliberately brief, statistically significant quantitative information has been provided where possible. This is usually given as Relative Risk, in keeping with the original source of the information. Cost-benefit issues are not considered.
In keeping with the original Protocols, these revised documents are designed to assist Health Authorities and Local Authorities in developing local strategies, purchasing high quality health care and identifying key areas for environmental research and action. It is anticipated, however, that they will be of value to all professionals in keeping abreast of the huge and increasing body of relevant literature and can provide an agenda for future action in a wide variety of settings. We anticipate that some of the conclusions reached will 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 team4.


The Healthy Environments Bulletin
The Healthy Environments Bulletin deals with the effect of the environment on health. The role of the environment in disease can be difficult to ascertain because of the enormous potential for interaction between a variety of risk factors. The Bulletin deliberately focuses on those aspects of the physical environment that are likely to have greatest impact on health including air quality, housing and environmental tobacco smoke. It also deals with the problem of noise, both because of its importance as a work-related disease and because it is increasingly a cause of societal concern.

The Bulletin does not deal with accidents since these are considered in the Injury Prevention Bulletin, whilst aspects of lifestyle are considered in the Healthy Living Bulletin.

The project team sought evidence to answer each of the following questions:

Published studies on environment and health are concerned almost exclusively with linking environmental factors with the aetiology of disease. Much of the evidence evaluated is therefore drawn from observational studies rather than randomised trials. Systematic reviews and meta-analyses were used where they exist. However, there is a dearth of well-designed research evaluating the health impact of environmental interventions. This imbalance is therefore reflected in the range of statements made in the Protocol.


  1. Welsh Health Planning Forum. Cardiff: Welsh Office NHS Directorate, 1993.
  2. Barker J, Weightman AL, Lancaster J.  Project for the Enhancement of the Welsh Protocols for Investment in Health Gain: Project Methodology 2.  Cardiff: Duthie Library UWCM, 1997.
  3. See Internal and External Review Groups - Contributers
  4. Contact: Health Evidence Bulletins - Wales, Duthie Library, UWCM, Heath Park, Cardiff, CF14 4XN.
  5. This table is adapted from the Bandolier system (derived from he 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 and the Database of Abstracts of Reviews of Effectiveness (DARE) in the Cochrane Library.
  6. This tabel is based on the Health Gain Notation 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.
  7. Relative risk = the ratio of risk of disease or death among the exposed to the risk among the unexposed.
  8. Health Evidence Bulletins - Wales: Injury Prevention. Cardiff Welsh Office, 1998.
  9. In preparation


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