BOHRF 2004 Evidence Review Methods |
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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)
| *** |
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
| 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
| 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 
.
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