Table 2.
Change of the association between child's season of birth and IQ at age 6 years with stepwise addition of covariates (n=6034)
| Child IQ at age 6 years |
|||||||||
|---|---|---|---|---|---|---|---|---|---|
| Season of birth | Adjusted for | Basic model: child gender and age at IQ assessment | Model 2: +maternal sociodemographic characteristics | Model 3: +maternal IQ | Model 4: +maternal nutritional intake and one-carbon biomarkers | Model 5: +child relative age in class and season at IQ assessment | Model 6: +vitamin D plasma levels | Model 7: +gestational duration and birth weight | Model 8: +fever during pregnancy and CRP levels |
| Spring | β (95% CI) p value | −1.24 (−2.31 to −0.17) 0.02 | −1.14 (−2.17 to −0.12) 0.03 | −0.87 (−1.87 to 0.14) 0.09 | −0.86 (−1.87 to 0.14) 0.09 | −0.75 (−1.91 to 0.40) 0.20 | −0.68 (−1.89 to 0.52) 0.27 | −0.59 (−1.80 to 0.61) 0.33 | −0.57 (−1.78 to 0.64) 0.35 |
| Summer | Reference | Reference | Reference | Reference | Reference | Reference | Reference | Reference | |
| Autumn | β (95% CI) p value | −0.52 (−1.56 to 0.51) 0.32 | −0.75 (−1.74 to 0.24) 0.14 | −0.63 (−1.60 to 0.34) 0.20 | −0.64 (−1.61 to 0.34) 0.20 | −0.53 (−2.25 to 1.18) 0.54 | −0.66 (−2.41 to 1.09) 0.46 | −0.63 (−2.37 to 1.12) 0.48 | −0.63 (−2.37 to 1.12) 0.48 |
| Winter | β (95% CI) p value | −0.84 (−1.93 to 0.26) 0.13 | −0.89 (−1.94 to 0.15) 0.09 | −0.66 (−1.69 to 0.36) 0.21 | −0.71 (−1.74 to 0.32) 0.18 | −0.76 (−2.28 to 0.77) 0.33 | −0.84 (−2.47 to 0.79) 0.31 | −0.76 (−2.39 to 0.86) 0.36 | −0.75 (−2.38 to 0.88) 0.37 |
| Seasonal trend | β (95% CI) p value | −0.40 (−0.74 to −0.07) 0.02 | −0.36 (−0.68 to −0.04) 0.03 | −0.27 (−0.58 to 0.05) 0.10 | −0.27 (0.59 to 0.05) 0.10 | −0.23 (−0.55 to 0.10) 0.18 | −0.18 (−0.53 to 0.17) 0.31 | −0.15 (−0.50 to 0.20) 0.39 | −0.14 (−0.49 to 0.21) 0.42 |
| Effect estimate change of seasonal trend (%) | Reference | 10.0 | 32.5 | 32.5 | 42.5 | 55.0 | 62.5 | 65.0 | |
| R2 (change)* | 0.020 | 0.088 | 0.036 | 0.003 | 0.001 | 0.001 | 0.01 | 0.001 | |
| P Value | <0.001 | <0.001 | <0.001 | <0.001 | 0.02 | 0.02 | <0.001 | 0.001 | |
Results from linear regression analyses. Values represent β, 95% CIs, p values and R2 change.
*First column R2. Please note that the R2 change of the covariates depends on the order of introduction to the model. The effects of the covariates in the basic model are given in online supplementary table S2.
CRP, maternal C reactive protein, mg/L.