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Hilary Thomson Medical Research Council Social and Public
Health Sciences Unit, Glasgow G12 8RZ Correspondence to: H Thomson hilary{at}msoc.mrc.gla.ac.uk
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Abstract |
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Objective:
To review the evidence on the effects of
interventions to improve housing on health.
Design:
Systematic review of experimental and
non-experimental housing intervention studies that measured
quantitative health outcomes.
Data sources:
Studies dating from 1887, in any
language or format, identified from clinical, social science, and grey literature databases, personal collections, expert consultation, and
reference lists.
Main outcome measures:
Socioeconomic change and
health, illness, and social measures.
Results:
18 completed primary intervention studies were identified. 11 studies were prospective, of which six had control
groups. Three of the seven retrospective studies used a control group.
The interventions included rehousing, refurbishment, and energy
efficiency measures. Many studies showed health gains after the
intervention, but the small study populations and lack of controlling
for confounders limit the generalisability of these findings.
Conclusions:
The lack of evidence linking housing and
health may be attributable to pragmatic difficulties with housing
studies as well as the political climate in the United Kingdom. A
holistic approach is needed that recognises the multifactorial and
complex nature of poor housing and deprivation. Large scale studies
that investigate the wider social context of housing interventions are required.
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What is already known on this topic
What this study adds
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Introduction |
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Poor housing has been used both as an indicator of poverty and as a target for interventions to improve public health and reduce inequalities in health.1 Although housing still has a prime place on the health inequalities agenda, it also has wider importance because small health effects can have a large impact at the population level.
Policy makers are also increasingly interested in measuring the health effects of social interventions (such as social housing) and in gathering evidence to shape policy. 2 3 Much of the research investigating the links between housing and health has been cross sectional, and these studies have shown strong independent associations between housing conditions and health. However, results of studies in small areas are difficult to generalise to other contexts. Observational studies have also shown strong independent associations between poor housing and poor health, but their results remain open to debate and interpretation.4
Experimental studies of the health impacts of housing would provide
stronger evidence. The randomised controlled trial has been regarded as
the gold standard experimental model to show the effects of
interventions in medicine. Such trials, however, are less common in
housing research, where there is less of a history of
experimentation.5 We carried out a systematic review of
intervention studies of the health effects of housing improvement.
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Methods |
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Search strategy
We searched the following databases: ASSIA (Applied Social
Science Index and Abstracts, 1987-2000), CAB Health (1973-2000),
DHSS-DATA (1983-2000), Embase (1974-2000), HealthSTAR (1975-2000),
Medline (1966-2000), PAIS (Public Affairs Information Service,
1976-2000), PsycINFO (1887-2000), SIGLE (System for Information on Grey
Literature in Europe, 1980-2000), Social SciSearch (1972-2000), Sociological Abstracts (1963-2000), Social Science Citation Index (1981-2000), Urbadisc, Cochrane Controlled Trials Database 2000 Issue
2, IBSS (International Bibliography of the Social Sciences), SPECTR
(Social, Psychological, Educational, and Criminological Controlled
Trials Register, searched December 2000), and the world wide web. Full
details of the search strategy are available from the authors.
Selection
We sought primary studies in any language that used experimental
or quasi-experimental approaches to examine the effects of housing
improvements. These included randomised controlled trials and
observational studies that used prospective or retrospective measures
of health. Our outcome measures were based on a social model of health
and included socioeconomic changes and illness based outcomes.
Housing interventions were defined as rehousing, and all physical
changes to housing were defined as infrastructure
for example
installation of heating, insulation, double glazing, and general refurbishment.
Assessment of validity assessment and data abstraction
Three reviewers critically appraised the included studies
according to the criteria (box). Studies graded as C were not
considered in the final assessment of the evidence. When reviewers' conclusions differed, the study was reviewed jointly by three reviewers. Data were abstracted by one reviewer (HT) and checked by a
second reviewer (MP). When data on the group of interest were not given
in the publication, we calculated them if possible
for example, new P
values were calculated using the relevant sample sizes.
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Criteria for assessing strength of evidence (adapted from NHS
Centre for Reviews and Dissemination method)6
Level A: prospective study, follow up rate >80% and for
Randomised controlled trial, or controlled study with comparable control group Objective assessment of health outcome(s) Level B: prospective study with control group Limited control of confounding Appropriate assessment of health outcomes Level C: prospective and retrospective studies that did not adjust for confounding factors Studies with biased assessment of health outcomes |
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Results |
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We identified 18 completed intervention studies (see BMJ 's website for details),7-29 the earliest dating from 1936.15 Six studies were identified from electronic databases (figure). Three studies examined the health impacts of rehousing based on medical need,7-10 11 examined the health effects of rehousing or refurbishment and renovation,11-23 and four assessed energy efficiency measures.24-29 Seven studies assessed housing improvement in the context of area or community regeneration. 11 12 15-17 19-21
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Eleven studies were prospective, of which six used control groups. 7 8 11-15 26 27 Three of the seven retrospective studies used a control group. 20 21 28 29
We also identified 14 ongoing housing intervention studies based in the United Kingdom (see BMJ 's website for details). These are investigating similar interventions to the completed studies. Seven of these ongoing studies are prospective and controlled; one is using a randomised stepped wedge design.30
Medical priority rehousing
All three studies of rehousing on the basis of medical need found
improvements in self reported physical and mental health. However, the
only prospective study was small,
7 8
and no study
controlled for the effects of possible confounding variables. One study
examined the effects on use of health services and found no clear
pattern.9
Rehousing, refurbishment and relocation or community regeneration
Two prospective controlled studies reported beneficial effects of
rehousing or refurbishment on health outcomes, including improvements
in mental health.11-14 Only one study had controlled for
confounding. This study showed an initial increase in illness episodes
in the intervention group at 9 months. At 18 months, however, the
intervention group showed a larger reduction in illness episodes
compared with the control group, although the absolute difference was
small (29 episodes/1000 people) and the rate of follow up was not
stated.
11 12
The other prospective controlled study
reported improvements in mental and physical health, but the study was
small and the comparability of the control group is
unclear.
13 14
Energy efficiency measures
Although the four studies that we identified all found that energy
efficiency measures improve respiratory and other symptoms, only one
study adjusted for potential confounding variables.27 High
rates of attrition in this and most other studies limit the
generalisability of these findings.
Use of health services and social effects
Some studies assessed the effects of improving housing on
use of health services; decreased visits to the general practitioner,
reduced likelihood of inpatient and outpatient use of health services,
and reduced prescribing of hypnotic and respiratory drugs were
reported. None of the evidence for these effects came from
methodologically robust prospective controlled studies.
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Discussion |
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We found few studies examining the effects of housing improvements on health, and the quality of the studies identified was generally poor. Improvements have been reported in overall self reported physical and mental health, as well as reductions in symptoms and use of health services. There is also some evidence of improvements in broad indicators of social inclusion such as neighbourliness and fear of crime. However, because of the methodological limitations of the studies, it is impossible to specify the nature and size of health gain that may result from a specific housing improvement. In particular, there are few large prospective controlled studies, and many studies are now quite old.
The effect of publication bias on our study also needs considering. Given the small positive effect sizes and small sample sizes, any summary of the published studies may overestimate the effects of housing improvements. In addition, the fact that we identified only six out of the 18 included studies using electronic databases suggests that systematic reviews of non-clinical interventions need to develop specially tailored search strategies.
Difficulties in studying housing and health
Reasons for the lack of studies into the effects of housing on
health may include methodological difficulties and political obstacles.
There are many methodological difficulties inherent in assessing the
health effects of housing interventions. Poor housing conditions often
exist alongside other forms of deprivation, and housing interventions
rarely occur in isolation. This may affect the sociodemographics of an
area and make before and after comparisons problematic.20
Moreover, response and follow up rates in studies of deprived areas are
often low.
Other evidence
Sources of evidence other than experimental studies are also
important. Longitudinal studies have been recommended as a useful, if
expensive, study design in evaluating complex interventions such as
housing.35 For example, recent results from the 33 year
follow up from the longitudinal national childhood developmental
study show that poor housing adversely affects health in later
life. The study found a dose-response relation, with multiple housing
deprivation leading to greater risk of disability or severe ill health
in later life.36 Data from the Boyd-Orr cohort also show
that childhood housing conditions have an effect on adult health
independent of the effects of socioeconomic deprivation.37
Conclusion
The basic human need for shelter makes the relation between
poor housing and poor health seem self evident.42 Despite,
or perhaps because of, this intuitive relation, good research evidence
is lacking on the health gains that result from investment in housing.
We know little about the mechanisms of interaction of social factors
and the effects of poor housing over the lifecourse. There is also a
lack of comparative information on the costs and effects of specific
housing improvements, such as central heating or major refurbishment.
It is this type of evidence that is likely to be most valuable to
policy makers and housing providers. Large scale studies that
investigate the wider social context of housing improvements and their
comparative effectiveness and cost effectiveness are now required.
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Acknowledgments |
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We thank Professor Sally Macintyre for helpful comments on the manuscript, Julie Glanville and Su Golder for help with the searches, and Mary Robins for librarian support.
Contributors: HT contributed to the search strategy of the review, collection, and analysis of the data, and writing the paper and is the guarantor. MP contributed to the collection and analysis of the data and writing the paper. DM contributed to reviewing the studies and writing the paper.
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Footnotes |
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Funding: The authors are funded by the Chief Scientist Office of the Scottish Executive Department of Health.
Competing interests: None declared.
Tables giving full details of the
included and ongoing studies are available on the BMJ's website
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References |
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(Accepted 25 April 2001)
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