138 Chapter 8 Table 2. Mixed-model for FOHR 95% CI OR 2.5% 97.5% (Intercept) 0.756 0.677 0.845 Age at measurement § Tonsil position 1.021 1.012 1.030 Head circumference‡ 1.102 1.063 1.140 Closed lambdoid sutures< 1 year 1.103 0.971 1.266 Expected FOHR at 0 and 5 years by specific covariate values* Tonsil position† Expected FOHR 95% CI Age 0 Q1: 0.0 0.442 0.415 0.470 Q3: +8.6 0.486 0.449 0.524 Age 5 Q1: 0.0 0.343 0.327 0.360 Q3: +8.6 0.384 0.363 0.405 Head-circumference‡ Age 0 Q1: -0.66 0.434 0.403 0.467 Q3: 1.39 0.484 0.452 0.516 Age 5 Q1: -0.66 0.336 0.317 0.355 Q3: 1.39 0.382 0.362 0.400 Closed lambdoid sutures< 1 year Age 0 Open 0.462 0.431 0.493 Closed 0.487 0.456 0.518 Age 5 Open 0.361 0.345 0.378 Closed 0.385 0.355 0.415 CI: credible interval, OR: odds ratio, FOHR: fronto-occipital horn ratio, Q1: 1st quartile in observed data, Q3: 3rd quartile in observed data § The non-linear effect of age at measurement was used in the model, but cannot be represented by a single parameter estimate and the corresponding estimates do not have direct clinical interpretation † Values represent tonsil position in mm relative to the foramen magnum, where tonsillar herniation past the foramen magnum is represented as positive numbers, and a position above the foramen magnum as negative numbers ‡ in SD * The other covariates were set to reference/median values (tonsillar position: +3.88 mm, head-circumference: 0.51 SD, lambdoid suture: open)
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