Table 1.
Descriptive statistics for the main analytic data set ages 13–14 years (n = 183 centers).a
| Median (interquartile range) | Spearman correlation with | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Variable | Time period | Asthma prevalence | PM2.5 | NO2 | O3 | |||||||
| Sex (ISAAC Phase Three, ages 13–14 years) | ||||||||||||
| % boys in sample | ≈ 2000–2003 | 49.2 (47.1–51.5) | –0.082 | 0.134 | 0.296# | 0.201** | ||||||
| Disease (ISAAC Phase Three, ages 13–14 years) | ||||||||||||
| Asthma prevalence (%) | ≈ 2000–2003 | 5.05 (3.34–8.04) | — | –0.412# | –0.198** | –0.489# | ||||||
| Climate/altitude | ||||||||||||
| Daily temperature (°C) | 1991–2000 | 18.7 (12.7–24.9) | 0.159* | –0.033 | –0.358# | –0.060 | ||||||
| Water vapor pressure (hPa) | 1991–2000 | 14.5 (10.8–22.5) | 0.209** | –0.183* | –0.372# | –0.196** | ||||||
| Precipitation (mm/month) | 1991–2000 | 81.5 (50.3 –125.1) | 0.217** | –0.347# | –0.248# | –0.355# | ||||||
| Altitude (m) | NA | 85 (22–458) | 0.006 | 0.099 | –0.019 | 0.102 | ||||||
| Economic/population | ||||||||||||
| GNI per capita (US$) | 2001 | 1,960 (1,020–9,800) | –0.023a | –0.022a | 0.537a,# | –0.132a | ||||||
| Population density (thousands per 0.1° × 0.1° grid square) | 2005 | 167 (47.0–514) | –0.038 | 0.302# | 0.408# | 0.218** | ||||||
| Pollution | ||||||||||||
| PM2.5 (µg/m3) | 2001–2006 | 14.6 (8.2–19.4) | — | — | 0.468# | 0.617# | ||||||
| NO2 (ppbV) | 2005 | 0.77 (0.36–2.00) | — | — | — | 0.332# | ||||||
| O3 (ppbV) | 2005 | 53.2 (40.4–61.7) | — | — | — | — | ||||||
| NA, not applicable. aCorrelations for GNI per capita (available only at country level) are with country-level variables (defined as in Equation 1). There are 83 countries. All other correlations are across all 183 centers. *p < 0.05, **p < 0.01, #p < 0.001. | ||||||||||||