A Systematic Review of Sustainable Housing Examples: Results Synthesised from the PUBMED and ScienceDirect Databases

Accommodation for both humans and animals could have impacted on both occupants and environments at the same time. Consequently, sustainable housing with a systematic life-cycle assessment has been one of the research focuses in the recent decades with an aim to lessen negative impacts on natural environments and to optimise occupant health and wellbeing. Following this context, it was aimed to carry out a systematic review to synthesise existing literature published until September 2014 on sustainable housing examples from two largest research databases covering health and development research. There were 10 research articles found in the PUBMED database and other 8 research articles additionally found in the ScienceDirect database. Sustainable housing examples mainly came from Americas and Europe while a few were from Africa and Australia. No sound studies were found from Asia. The research quality of these studies was from low to medium only. Research into sustainable housing examples for either humans or animals is still limited and research methodology was not robust enough to give clear indications on the promotion of sustainability in different housing environments. Collaborations between epidemiologists and engineers to employ real-life housing examples and to conduct rigorous research and follow-ups are therefore suggested.


Introduction
Housing conditions affect occupants continuously and health interventions have shown a positive association between housing investment or improvement and occupant health. 1 A recent global study has revealed that at least ¼ residents in every included country, being wealthy or not, would view housing improvement as top priority in the social and political agenda, with a particularly higher percentage in less wealthy countries (i.e. over 60%; such as in Andorra, Turkey, Ethiopia, Rwanda, and Mali). 2 In the same survey, it was also found that people who reported poorer health conditions considered housing as top priority (OR 4.56, 95%CI 1.10-18.81,P=0.036).Housing problems are prevalent in every society.There were several studies investigating the effects of different housing types on human health and cardiovascular biomarkers, 3,4 and in particular in children.Moreover, environmental chemicals were found to mediate the effect of old housing on occupant health, 5 although the sources were not available to be completely investigated.Accommodation for both humans and animals could have impacted on both occupants and environments at the same time.Consequently, sustainable housing with a systematic life-cycle assessment has been one of the research focuses in the recent decades with an aim to lessen negative impacts on natural environments and to optimise occupant health and wellbeing. 6Following this context, it was aimed to carry out a systematic review to synthesise existing literature on sustainable housing examples from two largest research databases covering health and development research.

Results and Discussion
Of all the 110 identified published articles from the PUBMED database using keywords including "sustainability" and "housing", only 10 research articles (published in 2001-2013) met the inclusion criterion (research articles describing housing examples in relation to sustainability) and included for presentation.Table 1 presents publication year, journal, author(s), research question(s), study design and results from each of the included research articles.Critique on study limitations were discussed as well.Overall, the study samples used were small and those sustainable housing examples mainly came from Americas and Europe.Of all the 214 identified published articles from the ScienceDirect database using the same search strategy (some of them were the same found in the PUBMED database), only other 8 research articles (published in 2006-2014) met the inclusion criterion mentioned above and included for presentation.

No studies of high quality on sustainable housing examples
In Table 3, summary scores of research quality for each included research article were calculated and are shown separately.Overall, the research quality was low to medium only.The main problems were lack of clear description on analysis process and a vigorous research methodology.

Experimental Section
The present study employed a systematic review approach, which is used to provide research evidence for future research and policy use.According to Khan, et al, 7 a review earns the adjective systematic if it is based on a clearly formulated question, identifies relevant studies, appraises their quality and summarises the evidence by use of explicit methodology.Following this framework, the proposed 5 steps, namely "Framing questions for a review", "Identifying relevant work", "Assessing the quality of studies", "Summarising the evidence" and "Interpreting the findings", of conducting a systematic review were therefore adopted in the current study.Analysis of quality of the included quantitative and qualitative studies was based on the assessment checklists proposed by Kmet, et al. 8 For quantitative studies, there are 14 criteria to score each article.For qualitative studies, there are 10 criteria.For each criterion, if an article fully met, then the score would be 2.However, if an article only partially met, the score would be 1.No score would be given if an article did not meet the criterion.Following this calculation, the maximum scores would be 28 and 20 for quantitative and qualitative studies, respectively.
The inclusion criterion of literature was research articles describing housing examples in relation to sustainability.Therefore, keywords used were "sustainability" and "housing".Other articles dealing with parts of housing system from an engineering perspective were excluded.Since this study is only a literature search and synthesis by extracting published research articles from two largest research databases, namely PUBEMD and ScienceDirect, covering health and development research until September 2014, no further ethics approval was required.

Conclusions
The included research articles from the current systematic review are fewer than expectation, given that the sustainability has been one of the research focuses in recent years.Sustainable housing examples in research articles were published only since 2001.Although there could have been some proposed sustainability indexes from environmental scientists, engineers or architects, 27,28 those have not been systematically tested in real life.In addition, most of the articles describing housing system and environmental sustainability did not mention the relationships among housing repair, occupant wellbeing and environmental sustainability.In other words, it is not known whether the change of housing system could actually bring more repair that would chronically and cumulatively result in financial harm and environmental damage.In sum, research into sustainable housing examples for either humans or animals is still limited and research methodology was not robust enough to give clear indications on the promotion of sustainability in different housing environments.Collaborations between epidemiologists and environmental professionals to conduct rigorous research and follow-ups on improving sustainable housing and occupant health in real life in the next decades are strongly suggested.

Table 2
also presents publication year, journal, author(s), research question(s), study design and results from each of the included research articles while critique on study limitations were discussed as well.Overall, the study samples used were also small and those sustainable housing examples came from Americas, Europe, Africa and Australia.There were no same housing examples in different published research articles observed.

Table 1 .
List of the included articles from the PUBMED database.

Table 2 .
List of the included articles from the ScienceDirect database.

Table 3 .
Summary scores of research quality for each included research article.