Arrandale et al. the investigation (Lambert et al. 2003; Paulson 2006). The homeowner has the right to under- stand the meaning of the results and how they affect both the occupants and the structure itself. For these reasons it is important to have a plan to communicate results to participants in a meaningful way. This could include both visual and written interpretations of the results, and the summary could be generic for each quartile (for example) of the data rather than specific to each home. Conclusions Ideally, environmental samples would be obtained using accurate and precise methods during the relevant windows of exposure and processed appropriately to permit prompt analysis for existing hypotheses and the pursuit of additional research questions in the future. In reality, decisions are made based on available resources, the research interest of the individual researchers, and priorities of the funding orga- nizations. A single study cannot do everything. Recognizing these limitations, there remains a significant need for better exposure assessment in epidemiological studies. Exposure levels will vary between indi- viduals and also over time and space within individuals. We must gain more knowledge of the biological mechanisms underlying dis- ease to properly identify the windows of expo- sure, the relevant duration of exposure, and possible latency period(s). Multiple measures of exposure must be collected where pos- sible. Modeling of exposures as well as subject participation in data collection may ease the burden of measuring exposure more frequently, but both require evaluation. Researchers have to make decisions about what to measure, which microenvironment to measure in, where exactly to measure within each microenvironment, which methods to employ, and at what time point(s) to meas- ure. These decisions involve tradeoffs between the accuracy and precision of exposure meas- ures, the completeness of the exposure assess- ment, and the statistical power of the study, as well as the resources available and burden that will be placed on participants. Hypotheses about relevant exposures need to be based on knowledge of biological mechanisms, gene– environment interactions, and physiological development. Exposures of interest can be pri- oritized based on many levels, including pub- lic health importance, measurement ability, biological mechanism of action, and the future use of the data collected. Gene–environment interaction studies are an area of immense research interest but are at even higher risk of being underpowered. Better exposure assessment and more precise pheno- type ascertainment are the most efficient ways to increase the power in such studies. Secondarily, data pooling can also increase power, permit 596 analyses not possible with smaller sample sizes, and increase the probability of replicable results. Additionally, there is a need to consider data compatibility across cohorts when design- ing a new study. Exposures should be priori- tized not only on the goals of the individual study but also on the power that may result from pooling data from multiple studies. Summary Several areas of exposure assessment can be targeted for immediate improvement in stud- ies of childhood asthma: • Planning for data pooling, as well as storage of samples for future analyses, at the outset of cohort studies; • Refining the exposure assessment protocol, questionnaires, and/or measurements to account for relevant time periods of exposure; • Engaging participants in the measurement of exposure to permit the collection of mul- tiple samples over the course of the study; • Increased use of hybrid methodologies that combine pollutant data with atmospheric fate and transport, exposure, and dose models. Ultimately, exposure is best characterized through a combination of information sources, and future studies should strive to improve their exposure-assessment strategy. Collectively, this information may yield unique exposure profiles common among subsets of the popula- tion that will help characterize children at risk and improve health outcomes. 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