Using evidence within HIA
Existing reviews of evidence – or ‘off-the shelf‘ evidence
Using existing reviews of evidence is common in the HIA process, since the timeframes and resources available for finding evidence are often short.
It is important to be systematic when searching for reviews. It is highly unlikely that different reviews will reach identical conclusions, so presenting evidence from several reviews is valuable. Conclusions may vary because of different aims and objectives, different studies being included and excluded, and because the personal opinions of the authors may be reflected in the work.
Key reviews for HIA
The types of reviews most useful for HIA practitioners are those that look into both the positive and negative impacts of an intervention; those that describe how poor health outcomes may be reversed; those that describe how a proposal may act on inequalities; and economic evidence. An example is "Housing improvement and health gain: a summary and systematic review" that investigates how interventions in the housing sector may lead to improved health.
Such reviews are also useful for providing information about the possible mitigation of negative effects, or providing ideas for alternative options.
Other reviews for use in HIA
A great number of observational studies and reviews of such studies show an association between poor housing and poor health, but do not provide convincing evidence about the effectiveness of interventions. This type of evidence can be used to point to the interventions that should be tried, but does not prove that they work. Such studies provide useful background information for an HIA, but basing recommendations on such information is less than ideal.
Where can I look for reviews?
Several HIA web sites provide reviews about the effectiveness of interventions. Searching this web site and the HIA Gateway are good starting points. Many other organisations and collaborations have a specific responsibility for undertaking reviews and are listed in the Health Development Advice (HDA) evidence base.
Conducting one's own literature search remains very worthwhile. Whenever new or additional reviews are discovered, it would be constructive to inform the main HIA websites in order to help future practitioners.