What is the reliability and validity of the SDQ in 5-6 year old children?
In chapter 2 and 3 the validity and reliability of the parent and teacher reported SDQ are described in a population of 5 to 6 year old children. The results from these studies show that the validity and the reliability of both the parent and teacher reported SDQ are satisfactory. However, there are some concerns about the subscales of the SDQ.
The total difficulties score and the subscale hyperactivity/inattention problems have good psychometric properties on the parent as well as the teacher SDQ. The subscales emotional symptoms and prosocial behaviour have good properties on the teacher SDQ only. All other subscales show not as good psychometric properties especially in subgroups by ethnic background.
In more detail, the original five factor structure of the parent and teacher reported SDQ was confirmed by principal component and confirmatory factor analyses. The five factor structure was also found in other studies [1, 2]. Van Leeuwen et al. [2] also tested a three-factor solution, but this did not improve model fit. Additional analyses in our population using a three-factor solution also did not show improved model fit. Interrater agreement was acceptable for the total difficulties score and three subscales, but not for the conduct problem and prosocial behaviour scale. This is in line with research among older children [2, 3]. It is possible that for parents these behaviours are more difficult to observe and rate, because teachers see children interact more often with other children in the classroom. Another explanation is that these behaviours are more influenced by the setting (e.g. classroom versus home) or that subjective norms of parents and of teachers differ more with regard to these types of behaviour.
The internal consistency of the total difficulties score and the hyperactivity/inattention scale of the parent reported SDQ was acceptable. Internal consistency of the parent SDQ was not acceptable for the four other subscales. The internal consistency of the teacher SDQ was generally higher than of the parent SDQ, only for the scales conduct and peer problems the internal consistency was below acceptable. Our findings are comparable to studies on older children where weighted mean alphas for almost all subscales of the parent SDQ were lower than 0.7 and weighted mean alphas for the teacher SDQ on conduct problems and peer problems were lower than 0.7. [3]. Because the scales contain just five items, it should be kept in mind that scales with a small number of items are generally less reliable than scales with more items [4]. Another explanation for lower reliability of the subscales is that the items are less one- dimensional than assumed. For instance, the conduct problems scale inquires about aggressive behaviour as well as rule-breaking behaviour. For all scales except the peer problems scale, concurrent and divergent validity of the parent and teacher SDQ was acceptable and implies that, as hypothesized, the SDQ scales correlate with CBCL/TRF scales. Overall these findings are in line with other research. The concurrent validity found in this study is slightly lower than that found by Goodman et al. [5] but is similar to that found in children aged 8-16 years in the Netherlands [6] and in children aged 5-8 years in Flanders [2, 5].
Are there differences by gender or by parental education level?
Mean scores on the parent and teacher SDQ differ between subgroups by gender and parental education level. In general, mean scores in boys and children with a low
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parental education level were higher than in girls and children with a middle or high parental education level, except for the prosocial behaviour scale. The outcomes of reli- ability and validity measures also show differences in subgroups by gender and parental education level. In more detail, the reliability and validity of the parent and teacher SDQ are better in males than females. When analyzed by parental education level, we found better internal consistency for parents with a low education level. However, differences between gender and parental education level were small and conclusions on the ac- ceptability of the psychometric properties were the same for all subgroups (chapter 2). The findings in subgroups by gender are comparable to other studies [1, 2, 6-12]. As far as we know there are no other studies where differences in reliability and validity of the SDQ in subgroups by parent educational level were examined.
Are there differences according to ethnic background?
Mean total difficulties scores on the parent and teacher SDQ differ between subgroups by ethnic background. In general children of Dutch ethnic background have lower total difficulties scores than children of ethnic minority groups. There are also differences in reliability and validity of the parent and teacher reported SDQ between ethnic groups in 5 to 6 year olds. These differences appear mainly on the subscales. However, the total difficulties score of the parent and teacher SDQ is valid and reliable for all ethnic groups within the Dutch society (Chapter 3). Differences between ethnic groups were also found in other studies [13, 14]. It is possible that in non-western countries, certain behaviours are an expression of other emotions than in western countries or that these items are interpreted or valued differently and therefore correlate higher with items from other subscales [15, 16]. For example, in collective societies children learn to sup- press the expression of anger because this is regarded as disrespectful; in individual societies, the expression of anger is seen as assertive behaviour [15]. Since we found differences in reliability and validity measures of the teacher-rated SDQ between ethnic groups, it is possible that the difference in child behaviour at home and at school is more prominent for non-Dutch children. Furthermore, it is also possible that stereotypes and biases can influence the teacher report with regard to emotional and behavioural problems in non-Dutch children [17, 18].
What is the discriminative power of the SDQ in 5 to 6 year olds?
In chapter 4 the discriminatory power of the parent and teacher reported SDQ is described and differences by gender and ethnic background are explored. The total difficulties score of the parent and teacher SDQ shows a good discriminatory power in a total population of 5 to 6 old year children as well as for subgroups by gender and ethnic background when compared with a clinical score on the CBCL/TRF and in comparison with a clinical sample. This indicates that the total difficulties score of
the parent and teacher SDQ is suitable for screening purposes in the preventive child health care. This is in accordance with what is generally found in older age groups [3]. In general, the discriminatory power of the total difficulties score on the parent and teacher SDQ determined by using a clinical score on the CBCL/TRF as reference was slightly better in all groups than when using a clinical sample as reference. This is not very surprising. The SDQ and the CBCL/TRF both are developed to measure psychosocial problems. Therefore a high AUC was expected. The clinical sample consists of children entering in to Youth (Health) Care institutions. These children are not always entering care for their own psychosocial problems, but may also enter care due to adversities in their direct environment such as (social emotional) problems of other members of the family, domestic violence, abuse, educational or pedagogic problems. This may have contributed to the lower observed AUC in the clinical sample. The results of this study can also be used in choosing an appropriate cut off. Before choosing a cut off it is necessary to clearly state the situation and the purpose of the screening because from our results it appears that cut-offs differ between reference measures for the teacher SDQ and in subgroups by gender and ethnic background for both informants. In general cut offs, when determined by a reference measure, appear to be lower than the p90. Furthermore, cut offs appear to be lower in comparison with a clinical group than in comparison with the CBCL/TRF.
To summarise, in the first part of this thesis the reliability and validity of the SDQ were examined in a population of 5-6 year olds. The total difficulties score of the parent and teacher SDQ appears to be valid and reliable for screening in young children. The total difficulties score is valid and reliable in subgroups by gender, ethnic background and parental education level. The reliability of the subscales peer problems, prosocial behaviour and conduct problems appear to be less valid and reliable. Therefore, we recommend only using the total difficulties score for early detection purposes. Scores on subscales can only be used to give direction during the child’s health assessment. These scores cannot be used on their own for early detection.