A number of medical and environmental engineering studies have looked at the relationship between exposure to indoor air pollution and student health and performance and, indeed, many find negative associations. However, the vast majority suffer from a lack of sufficient data, resulting in small sample sizes and being unable to convincingly control for potential confounding variables so that causal effects cannot be reliably inferred. 11 Still, several studies that utilize longitudinal data or otherwise have strong designs have found some evidence that improved indoor environmental conditions positively affect student health and academic performance. Smedje and Norback (2000) find that the installation of new ventilation systems improves school indoor air quality and decreases the prevalence of self-reported asthmatic symptoms. Approximately 1500 students (1st, 4th, and 7th graders)from 39 schools in Sweden completed a health-related questionnaire in 1993 and again in 1995. Between these dates, new ventilation systems were installed in several of the schools, affecting 10% of questionnaire respondents. Measurements of environmental factors were taken in 100 classrooms in both 1993 and 1995 and in both treated and non-treated classrooms.These measurements suggest that the classrooms that received new ventilation systems experienced larger increases in ventilation rates and larger decreases in humidity and concentrations of CO2, formaldehyde, other VOCs, respirable dust, and total mold over time. Furthermore, while the reporting of asthmatic symptoms increased over time in all schools, it was less pronounced in schools with new ventilation systems.12
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