Page 47 - Sample Moderate prematurity, socioeconomic status, and neurodevelopment in early childhood

Effects of SES on behavioural and emotional problems
participating MP and term-born children were 93.3% and 95.1%, respectively. This led to a total of 1458 children in this study: 915 MP children and 543 term- born children.
Assessment of socioeconomic status
We determined SES on the basis of the three most frequently used measures,
i.e. education, income, and occupation.19,20 Data on the highest completed
educational level of both parents were collected by a general questionnaire when
the participating children were aged 4 years. The following categories were
defined: primary school or less, low-level technical and vocational training (<12
years’ education), high school or medium-level technical and vocational training
(12 to 16 years’ education), and university or high-level technical and vocational
training (>16 years’ education). At the same time, parents were asked to indicate
their net monthly family income in euros: ≤ 850; 851 to 1150; 1151 to 1750; 1751
to 3050; 3051 to 3500; and > 3500. Data on occupational level were collected 4 retrospectively from the medical birth registers kept by the PCH centres. We
classified the occupational level of both parents according to the International Standard Classification of Occupations.21 Next, we computed a composite SES score on the basis of five indicators: educational level of father, educational level of mother, family income, occupational level of father, and occupational level of mother. Information on these indicators was available for 96%, 99%, 77%, 82%, and 72% of the participating children, respectively. We ranked and standardised each of the indicators and computed the mean SES, with all indicators that were available for each child. Subsequently, a composite and standardized SES measure was computed, a continuous variable with a mean of 0 and a standard deviation (SD) of 1. Additionally, for descriptive purposes, we determined three categories of SES: 1) low, scores more than 1 SD below the mean of the standardized SES; 2) intermediate, scores between mean +/- 1 SD; and 3) high, scores greater than mean + 1 SD.
Behavioural and emotional outcomes
We measured behavioural and emotional problems at age 4 years, using the Dutch version of the Child Behavior Checklist (CBCL) for 1.5-5 years.22,23 This checklist has good psychometric properties and is widely used in a variety of health care settings and for research purposes.23 The reliability and validity of the problem scales were confirmed for the Dutch version of the CBCL.22,25 It consists of 99
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