Table 3.

Conventional regression analysis of association between quarterly 1-hr maximum O₃ concentrations (ppb) and hospital discharges for asthma, birth to 19 years of age: SoCAB 1983–2000.

Regressiona	O3 parameter estimate	Robust SE	p-Value
O3 forced into regression b	1.4 × 10−6	3.5 × 10−7	5.0 × 10−5
O3 not forced into regression	1.4 × 10−6	3.5 × 10−7	5.0 × 10−5

^aThe DSA was run with 29 candidate variables that were marginally associated with the outcome and O₃ (p-value < 0.05). The DSA was run with 10 different random data splits and selected the same model for all 10 runs for the forced model and 8 times for the unforced model. The two models that differed included an O₃ term. PM₁₀ was not selected into the analyses when either all measurements were used or when measurements were restricted to those directly measured (1988–2000). To convert 1-hr maximum O₃ to 8-hr (0100–1800 hours) mean, divide the 1-hr maximum by the following conversion factor: 1.3279 (± 9.97 × 10⁻⁴). For example, an 8-hr maximum of 70 ppb corresponds to a 1-hr maximum of 93 ppb in our data. The conversion factor is based on the linear regression of 1-hr maximum on the 8-hr maximum (t-value, 1330.58).

^bThe DSA selected 7 other terms in addition to O₃: white race, white race³ (cubed), income = $20,000–$39,999, average temperature for the quarter, relative humidity³, median income as a continuous variable, foreign born. Units are increases in discharges in total age-specific population per ppb (see Supplemental Material for details).