The results of the analysis of each study of the association of CO2 with health and perception outcomes are presented in Table 6, using the same format as Table 4. Findings are organized by outcomes, and within these by the highest CO2 concentration. Seventeen of the 32 assessments found that a higher CO2 concentration was significantly associated with a worsening of at least one outcome. Out of 18 assessments with SBS symptoms as outcomes (including studies with naturally ventilated buildings), 9 (50%) found a significantly higher prevalence of symptoms with higher CO2 concentrations. Relative risks and odds ratios were reported in fewer CO2 studies than ventilation rate studies. Relative risks for symptoms in the higher CO2 groups ranged up to 1.85 (Sieber et al., 1998). An odds ratio of 8.0 for ln (CO2 concentration) with non-specific symptoms was reported by NIOSH (1991). In addition, some studies found a dose-response relationship between outcomes and CO2 concentration (Bright et al., 1992; Sohn et al., 1994). Restricting the review to findings of the ten studies reported in peer-reviewed articles eliminated most of the evidence for relationships. The CO2 concentrations in the studies varied considerably. Table 7 illustrates that the percentage of studies with a significant association between CO2 concentration and SBS symptoms increased as higher concentrations of CO2 were included in the study