BOHRF 2004 Evidence Review Methods

Evidence Review Methods for the British Occupational Health Research Foundation (BOHRF) Occupational asthma guidelines.

Introduction

This evidence review concerns the occupational health aspects of the prevention, identification and management of occupational asthma. The review began with a systematic search for all published, methodologically sound and original scientific studies. The methodology of the review may be best summarised as systematic searching plus rating of the strength of the evidence plus a narrative overview by agreement between two experienced and independently minded reviewers.

Literature searches

The literature was searched using standard methods. MEDLINE and EMBASE were searched systematically from 1966 and 1974 respectively to the end of June 2004 for relevant articles published in all languages, using a number of search terms including:
  • occupational asthma
  • agents known to cause occupational asthma, asthmagens

Additional searching included; personal bibliographies, selected internet searches, citation tracking, scanning of relevant journals in the field and papers known to be 'in press' at the end of June 2004.

More than 2,500 titles and abstracts were considered. Narrative reviews were excluded. Abstracts were reviewed independently by two reviewers to identify papers to be requested for review. 474 papers were obtained and independently critically appraised and assessed for methodological quality, using a standard proforma. Where reviewers disagreed about the score of the paper or its relevance to this research, they discussed it to reach resolution. Where resolution was not achieved, a third reviewer was involved. At this stage, further references were excluded and pertinent data from the remaining 223 papers were entered into an evidence table. The main conclusions are described in the evidence table. This table was reviewed in order to formulate evidence statements and recommendations.

Evidence Statements

Criteria for grading evidence and recommendations are designed principally to guide inferences about the effects of treatment. Other hierarchies are needed to answer questions about aetiology, diagnosis, disease frequency and prognosis, the areas in which most research into occupational asthma has been focused. Since there are few systematic reviews and randomised controlled trials, there is scarce level 1 evidence as defined by the revised Scottish Intercollegiate Guidelines Network (SIGN) grading system (2000). To overcome this limitation we graded the strength of evidence for each statement using both the SIGN system and the Royal College of General Practitioners (RCGP) three star system (1995) as modified in the Swedish Council on Technology Assessment in Health Care report for scientific studies and the BOHRF Occupational Health Guidelines for the Management of Low Back Pain at Work.

RCGP (Three Star System)

Rating Level of Evidence Source of Evidence
*** Strong Evidence Provided by generally consistent findings in multiple, high quality scientific studies.
** Moderate Evidence Provided by generally consistent findings in fewer, smaller or lower quality scientific studies.
* Limited or Contradictory Evidence Provided by one scientific study or inconsistent findings in multiple scientific studies.
- No Scientific Evidence Based on clinical studies, theoretical considerations and/or clinical consensus.

As there are very few randomised controlled trials and since these do not apply to health surveillance, susceptibility to disease or the sensitivity and specificity of screening and diagnostic procedures in occupational asthma, high quality scientific studies were taken to be major epidemiological surveys and prospective cohort studies. Other, scientifically weaker, studies included retrospective, cross-sectional or uncontrolled cohort studies and case series.

Revised SIGN grading system - Levels of Evidence

Rating Levels of Evidence
1++ High quality meta analyses, systematic reviews of randomised controlled trials or randomised controlled trials with a very low risk of bias
1+ Well conducted meta analyses, systematic reviews of randomised controlled trials or randomised controlled trials with a low risk of bias
1- Meta analyses, systematic reviews of randomised controlled trials or randomised controlled trials with a high risk of bias
2++ High quality systematic reviews of case-control or cohort or studies
High quality case-control or cohort studies with a very low risk of confounding, bias, or chance and a high probability that the relationship is causal
2+ Well conducted case control or cohort studies with a low risk of confounding, bias, or chance and a moderate probability that the relationship is causal
2- Case control or cohort studies with a high risk of confounding, bias, or chance and a significant risk that the relationship is not causal
3 Non-analytic studies, e.g. case reports, case series
4 Expert Opinion

Evidence linking is to the most comprehensive and most recent source available. Where possible this is to a systematic review, which should include all of the earlier, original studies in that area. Direct reference to original studies is made where there is no systematic review, where they are not included in the review(s), or where they are necessary to support an important point.

Clinical judgement is necessary when using evidence statements to guide decision-making. Weak evidence statements on a particular issue or effect do not necessarily mean that it is untrue or unimportant but may simply reflect insufficient evidence.

Reccomendations

The guidelines include recommendations that follow each evidence statement or set of evidence statements. Recommendations are written as far as possible in precise, behaviourally specific terms . They are graded according to the modified RCGP three star system (1995) and the revised SIGN grading system for recommendations (2000).

Revised SIGN grading system - Grades of reccomendation

Grade Levels of Evidence
A At least one meta analysis, systematic review, or randomised controlled trial rated as 1++, and directly applicable to the target population; or a systematic review of randomised controlled trials or a body of evidence consisting principally of studies rated as 1+, directly applicable to the target population, and demonstrating overall consistency of results
B A body of evidence including studies rated as 2++, directly applicable to the target population, and demonstrating overall consistency of results; or extrapolated evidence from studies rated as 1++ or 1+
C A body of evidence including studies rated as 2+, directly applicable to the target population and demonstrating overall consistency of results; or extrapolated evidence from studies rated as 2++
D Evidence level 3 or 4; or extrapolated evidence from studies rated as 2+

Good practice points

The guidelines include good practice points where there is no, and nor is there likely to be, research evidence. They are based on the clinical experience of the research-working group, legal requirement or other consensus and are indicated in the guideline as Good Practice Point logo.

Comments

Please sign in or register to add your thoughts.


Oasys and occupational asthma smoke logo