Supplementary Table 1: Father's Reading at Age 2 and Child Language and Literacy Outcomes

Supplementary Table 1: Father's reading at age 2 and child language and literacy outcomes at 4 years of age, interaction analyses with mothers home reading

Father’s home Father reading and mother Variable reading mean (SD) reading Interaction coef Low High p (95% CI) CELF (language) Expressive 95.4 105.1 -4.1 (-11.1 to 2.9) 0.3 (16.5) (14.4) Receptive 91.9 100.7 -4.5 (-11.0 to 1.9) 0.2 (14.8) (13.8) SPAT (literacy) Intra-syllabic 6.8 7.4 -0.1 (-1.2 to 1.0) 0.9 (2.4) (2.4) Phonic 5.4 6.1 0.1 (-1.1 to 1.4) 0.8 Awareness (2.6) (2.8) Letter 8.9 10.6 Awareness (9.1) (9.0) -3.0 (-7.1 to 1.1) 0.2

1 Supplementary Table 1: Mother’s reading at age 2 and child language and literacy outcomes at 4 years of age, with coefficients indicating benefits to child outcomes for high mother reading compared to the reference of low mother reading

Mother’s home reading Model 4: Model 3 + child vocabulary and communication at 2 years Model 1: Unadjusted Variabl mean (SD) e Coef Coef 2 Coef Partial Coef Partial Low High p (95% Partial R p 2 p 2 p (95% CI) (95% CI) R (95% CI) R CI) CELF (langua ge) Express 96.5 (16.8) 104.3 7.7 <0.001 7.3 3.1 0.3 ive (15.0) (4.7 to (4.2 to 0.0489 <0.001 0.0069 0.1 0.0001 0.8 (-0.4 to 6.6) (-2.9 to 3.6) 10.8) 10.4) Recepti 93.0 (15.3) 100.1 7.2 <0.001 6.6 2.6 0.00 0.5 ve (14.1) (4.3 to (3.7 to 0.0459 <0.001 0.1 0.0002 0.7 (-0.7 to 5.8) 55 (-2.6 to 3.7) 10.0) 9.4) SPAT (literac y) Intra- 0.3 6.9 (2.2) 7.3 0.4 0.1 -0.1 syllabic 0.7 (-0.1 to 0.0044 0.2 0.0001 0.8 0.0004 0.7 (2.5) (-0.5 to 0.6) (-0.7 to 0.5) (-0.1 to 0.8) 0.8) Phonic 0.6 5.3 (2.5) 5.9 0.6 0.02 0.3 0.1 Awaren (0.1 to 0.0115 0.03 0.0025 0.9 0.0001 0.8 (2.9) (0.1 to 1.2) (-0.3 to 0.9) (-0.6 to 0.7) ess 1.1)

Letter 9.2 (9.0) 10.6 1.4 0.1 1.3 Awaren 0.8 -0.1 (9.1) (-0.4 to 3.2) (-0.4 to 0.0054 0.1 0.0013 0.7 0.0000 0.9 ess (-1.3 to 2.8) (-2.3 to 2.1) 3.1)

# R2 (unadjusted model) and partial R2 refers to the unique contribution of mothers reading in each model on child language and literacy outcomes

2 Supplementary Table 3: Father’s reading at age 2 using continuous scores and child language and literacy outcomes at 4 years of age, with coefficients indicating benefits to child outcomes

Model 4: Model 3 + child Model 2: Model 1 + Model 3: Model 2 + mother’s Model 1: Unadjusted vocabulary and communication Variable socioeconomic disadvantage reading at 2 years Coef Coef 2 Coef Partial Coef Partial Partial R p 2 p 2 p (95% 2 p (95% CI) (95% CI) R (95% CI) R R CI) CELF (language) Expressive 1.4 7.9% <0.001 0.3 1.4 0.8 (0.1 to (1.0 to 2.0) 6.9% <0.001 1.2% 0.02 (-0.3 to 0.2% 0.4 (0.9 to 1.9) 1.4) 0.9) Receptive 1.5 9.4% <0.001 0.7 1.4 1.0 (0.4 to (1.0 to 2.0) 7.8% <0.001 2.5% 0.001 (0.1 to 1.2% 0.02 (0.9 to 1.8) 1.6) 1.3) SPAT (literacy) Intra-syllabic 0.0 0.1 0.1 0.1 (-0.0 2.0% 0.004 1.5% 0.01 0.3% 0.3 (-0.1 to 0.02% 0.8 (0.0 to 0.2) (0.0 to 0.2) to 0.2) 0.1) Phonic 0.1 2.0% 0.004 0.1 0.1 0.1 (-0.0 Awareness (0.0 to 0.2) 1.6% 0.009 0.7% 0.1 (-0.1 to 0.3% 0.3 (0.0 to 0.2) to 0.2) 0.1) Letter 0.3 1.2% 0.03 0.0 0.3 0.1 (-0.2 Awareness (0.0 to 0.6) 1.0% 0.04 0.1% 0.4 (-0.4 to 0.01% 0.9 (0.0 to 0.6) to 0.5) 0.4)

# R2 (unadjusted model) and partial R2 refers to the unique contribution of mothers reading in each model on child language and literacy outcomes

Supplementary Figure 1: Association between parent home reading at 2 years and child language and literacy at 4 years, by social disadvantage

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