Table 3 Multilevel linear mixed-effects models showing associations of VP children’s LD with SDQ total scores at age 5 years.

Dependent variable:	SDQ total score
	Model 1 (N = 3067)	Model 2 (N = 3067)	Model 3 (N = 3020)	Model 4 (N = 2915)
*Fixed effects, coefficient (95% confidence interval)*
LD	0.02 (0.02, 0.03)***	0.02 (0.01, 0.03)***	0.02 (0.01, 0.03)***	0.02 (0.01, 0.03)***
Mother foreign country of birth	0.63 (0.16, 1.10)**	0.40 (−0.26, 1.07)	0.15 (−0.61, 0.92)	0.24 (−0.44, 0.92)
Mother’s education (high vs. low)			−1.45 (−2.26, −0.64)***	−1.43 (−2.27, −0.59)***
Single mother			−0.62 (−1.28, 0.04)	−0.60 (−1.14, −0.06)*
Household unemployment			1.73 (0.57, 2.90)**	1.45 (0.47, 2.42)**
Gestational age (weeks)				−0.08 (−0.19, 0.04)
Biological sex (female vs. male)				−1.53 (−2.01, −1.05)***
Multiple birth				−0.94 (−1.32, −0.56)***
Parity (multi- vs. primiparous)				−0.59 (−1.02, −0.16)**
Severe neonatal morbidity^a				1.25 (0.32, 2.18)**
BPD^b				1.01 (−0.34, 2.37)
Mother’s age (years)				−0.05 (−0.07, −0.02)**
constant		8.88 (7.54, 10.22)***	10.79 (8.64, 12.94)***	15.11 (11.53, 18.70)***
*Random effects by family*
SD (constant)		5.17 (4.83, 5.53)*	5.09 (4.75, 5.45)*	4.97 (4.63, 5.33)*
*Random effects by country*
SD (constant)		1.32 (0.96, 1.82)*	2.15 (1.83, 2.53)*	1.24 (0.86, 1.79)*
*Log-pseudolikelihood*		−14,827.37	−14,568.20	−13,852.13

LD linguistic distance, VP very preterm, SDQ Strengths and Difficulties Questionnaire, SD standard deviation, BPD bronchopulmonary dysplasia. Model 1 = unadjusted; Model 2 = LD and immigrant status adjusted for each other; Model 3 = additionally adjusted for mothers’ education, single mother status, household unemployment; Model 4 = fully adjusted, including LD, immigrant status, mothers’ education, single mother status, household unemployment, child GA, sex, multiple birth, mothers’ age, parity, BPD, severe neonatal morbidity; all models adjusted for IPW; for fixed effects *p < 0.05; **p ≤ 0.01; ***p ≤ 0.001; for random effects * marks a 95% confidence interval not including 0; significant effects of interest marked in bold;
^aSevere neonatal morbidity defined as a composite measure of cystic periventricular leukomalacia, intraventricular haemorrhage grades III or IV, severe necrotizing enterocolitis requiring surgery or peritoneal drainage, or retinopathy of prematurity at least stage 3;
^bBPD = Bronchopulmonary dysplasia with supplemental oxygen and/or ventilatory support (continuous positive airway pressure or mechanical ventilation) at 36 weeks of postmenstrual age.

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