RESEARCH ARTICLE

Parenting Practices at 24 to 47 Months and IQ at Age 8: Effect-Measure Modification by Infant Temperament Shiau Yun Chong1*, Catherine R. Chittleborough1, Tess Gregory1,2, Murthy N. Mittinty1, John W. Lynch1,3, Lisa G. Smithers1 1 School of Population Health, University of Adelaide, Adelaide, Australia, 2 Telethon Kids Institute, The University of Western Australia, Perth, Australia, 3 School of Social and Community Medicine, University of Bristol, Bristol, United Kingdom * [email protected]

Abstract OPEN ACCESS Citation: Chong SY, Chittleborough CR, Gregory T, Mittinty MN, Lynch JW, Smithers LG (2016) Parenting Practices at 24 to 47 Months and IQ at Age 8: EffectMeasure Modification by Infant Temperament. PLoS ONE 11(3): e0152452. doi:10.1371/journal. pone.0152452 Editor: James G. Scott, The University of Queensland, AUSTRALIA Received: June 16, 2015 Accepted: March 10, 2016 Published: March 30, 2016 Copyright: © 2016 Chong et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: ALSPAC data is made available to researchers by completing a proposal form (www.bristol.ac.uk/alspac/researchers/dataaccess/) and submitting it to the ALSPAC Executive ([email protected]). Funding: Ms Chong is funded by a University of Adelaide International Scholarship (www.adelaide. edu.au/) and a Fraser Mustard Centre PhD Scholarship (www.frasermustardcentre.sa.edu.au). Prof Lynch was supported by an Australia Fellowship from the National Health and Medical Research Council of Australia (grant number 570120)(www.

Cognitive development might be influenced by parenting practices and child temperament. We examined whether the associations between parental warmth, control and intelligence quotient (IQ) may be heightened among children in difficult temperament. Participants were from the Avon Longitudinal Study of Parents and Children (n = 7,044). Temperament at 6 months was measured using the Revised Infant Temperament Questionnaire and classified into ‘easy’ and ‘difficult’. Parental warmth and control was measured at 24 to 47 months and both were classified into 2 groups using latent class analyses. IQ was measured at 8 years using the Wechsler Intelligence Scale for Children and dichotomized ( 0 indicates the effect-measure modification is positive (the effect of the exposure and the effect modifier operating together is greater than the effect of each added together), RERI < 0 indicates the effect-measure modification is negative, RERI of 0 indicates there is no effect-measure modification on the risk-difference scale. Effect-measure modification on the risk-ratio scale is taken as: Ratio of RRs ¼

RRP1 T1 X RRP0 T0 RRP0 T1 X RRP1 T0

ð4Þ

If the ratio of RRs >1, the effect-measure modification is positive (the effect of the exposure and the effect modifier operating together is greater than the product of the effect of the exposure and the effect modifier). A ratio of RRs < 1 indicates the effect-measure modification is negative. A ratio of RRs = 1 means the effect of both exposures together is equal to the product of the effect of the two exposures considered separately. Analyses were performed using Stata version 13.0 (Stata Corp, College Station, Texas). Multiple imputation for missing data. We used multiple imputation by chained equation to impute missing data. Imputed datasets were generated under the missing at random assumption that the probability of data being missing is dependent on the observed data [50]. Variables included in the imputation model were parenting warmth, control, temperament, all confounders, breastfeeding, HOME inventory, all three measures of IQ (full-scale IQ, verbal IQ, and performance IQ) and interaction terms between parenting and temperament. Breastfeeding and HOME inventory variables were two auxiliary variables that were added to the imputation model because they are related to the outcome (IQ) and may enhance the prediction of missing values. Fifty cycles of regression switching were undertaken and 20 imputed datasets were generated. We used the multiple imputation then deletion technique [51] where analyses were conducted on respondents only with non-imputed outcome data. All analyses were performed on imputed data (n = 7,044).

PLOS ONE | DOI:10.1371/journal.pone.0152452 March 30, 2016

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Effects of Parenting Practices and Child Temperament on IQ

Table 3. Association between parenting warmth and control, and child temperament on children’s IQ (Imputed sample, n = 7,044). Model 1 β

Model 2

95% CI

p

β

-3.99, -2.42

Parenting Practices at 24 to 47 Months and IQ at Age 8: Effect-Measure Modification by Infant Temperament.

Cognitive development might be influenced by parenting practices and child temperament. We examined whether the associations between parental warmth, ...
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