Review Indoor and Built uilt Environment Indoor Built Environ 2010;19;3:311–326 Accepted: May 5, 2009 The Applicability of Epidemiological Methods to the Assessment of the Risks to Human Health of Indoor Air Pollution: An Overview T. Brown a P. Holmes b P.T.C. Harrison c a Institute of Environment and Health, Cranfield University, Cranfield, Bedfordshire, MK43 0AL, UK b Risk & Policy Analysis Ltd, Loddon, Norfolk, NR14 6LT, UK c PTCH Consultancy, Great Bowden, Market Harborough, Leicestershire, LE16 7HB, UK Key Words Epidemiological methods E Indoor air E Health risk E Exposure assessment E Weight of evidence E Environmental risk Abstract Western populations spend the vast majority of their time indoors, and can be exposed to a range of indoor pollutants that may have adverse effects on health. Scientists and regulators need to be able to understand and quantify the nature of the potential risks posed by the indoor environment. Epidemiological methods are available to investigate relationships between indoor pollutant exposure and health impacts, but involve many assumptions and have inherent uncertainties. To establish an accurate understanding of the knowledge base and a sound interpretation of the significance of the results obtained, it is essential that epidemiological study findings are not accepted uncritically and that the advantages/weaknesses of each design are fully under- stood. This overview identifies the strengths and weak- nesses of the various epidemiological techniques used to study indoor air pollution, and considers the place of epidemiological data within the wider weight of evi- dence considerations necessary to establish causality of associations and accurately determine potential risk. It is evident that epidemiology remains a key science in the study of associations between indoor air pollutants and diseases like asthma, and a number of recommendations are made that may improve the application of this methodology and the interpretation of derived results. Introduction During the last two decades, while there has been considerable public concern about, and much research activity directed at understanding, the health impacts of outdoor pollution, there has been only limited recognition of the importance of the indoor environment – in particular, indoor air quality – on health. This is despite the general UK and other Western populations spending the vast majority (80–90%) of their time indoors [1]. ß SAGE Publications 2010 Los Angeles, London, New Delhi and Singapore DOI: 10.1177/1420326X09342683 Accessible online at http://ibe.sagepub.com Terry Brown, Institute of Environment and Health, Cranfield University, Cranfield, Bedfordshire, MK43 0AL, UK. Tel. 0782 5457347, E-Mail t.p.brown@cranfield.ac.uk