Objectives This observational study examines the internal construct validity, internal consistency and cross-informant reliability of the Strengths and Difficulties Questionnaire (SDQ) in a New Zealand preschool population across four ethnicity strata (New Zealand European, Māori, Pasifika, Asian).
Design Rasch analysis was employed to examine internal validity on a subsample of 1000 children. Internal consistency (n=29 075) and cross-informant reliability (n=17 006) were examined using correlations, intraclass correlation coefficients and Cronbach’s alpha on the sample available for such analyses.
Setting and participants Data were used from a national SDQ database provided by the funder, pertaining to New Zealand domiciled children aged 4 and 5 and scored by their parents and teachers.
Results The five subscales do not fit the Rasch model (as indicated by the overall fit statistics), contain items that are biased (differential item functioning (DIF)) by key variables, suffer from a floor and ceiling effect and have unacceptable internal consistency. After dealing with DIF, the Total Difficulty scale does fit the Rasch model and has good internal consistency. Parent/teacher inter-rater reliability was unacceptably low for all subscales.
Conclusion The five SDQ subscales are not valid and not suitable for use in their own right in New Zealand. We have provided a conversion table for the Total Difficulty scale, which takes account of bias by ethnic group. Clinicians should use this conversion table in order to reconcile DIF by culture in final scores. It is advisable to use both parents and teachers’ feedback when considering children’s needs for referral of further assessment. Future work should examine whether validity is impacted by different language versions used in the same country.
- strengths and difficulties questionnaire
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Contributors PK conceived of the study, led on study design, project management, data analysis and dissemination. ACV, HE, KMMcP contributed to study design. ACV contributed to the data analysis. PK drafted the manuscript and is the guarantor. All authors revised it critically for important intellectual content and approved the final version for publication. All authors agree to be accountable for all aspects of the work.
Funding This work was supported by the Ministry of Health of New Zealand (grant number 341088).
Disclaimer All other authors declare no financial relationships with any organisations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work. The views and opinions expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the funder. The funding body has not had input into the design, data collection, analysis, interpretation of data, in the writing of the manuscript, nor in the decision to submit the manuscript for publication.
Competing interests PK, ACV, HE, KMMcP had financial support from the Ministry of Health of New Zealand for the submitted work; subsequent to the completion of this project and data analysis, KMMcP became the Chief Executive of the Health Research Council of New Zealand.
Patient consent Not required.
Ethics approval New Zealand Health and Disability Ethics Committee (Northern A, NTY/12/04/028/AM05) and the Auckland University of Technology’s Ethics Committee (12/163).
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement Quantitative data from the study can be obtained from the author, subject to the funder’s permission.
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