Structural validity and reliability of the Danish self-report Strengths and Difficulties Questionnaire among male and female students in vocational education and training

Objective: The Strengths and Difficulties Questionnaire (SDQ) is a widely used mental-health screening instrument among children and adolescents and increasingly used by welfare professionals. However, the psychometric properties of the SDQ-self report ((SDQ-S) among vulnerable youth are less well-known. This article assesses the internal consistency reliability, test-retest reliability and known groups validity of the Danish SDQ-S among vocational education and training (VET) students, many of whom are vulnerable.
Method: The SDQ-S was tested twice in a sample of 708 VET students (mean age: 17 years). Known groups validity was tested through gender differences in mean scores. Internal consistency was assessed using Cronbach’s alpha and test-retest reliability using Pearson’s correlation.
Results: Contrary to previous studies female SDQ scores were consistently higher on all scales except Conduct problems (no difference). Alpha for SDQ scales at T1/T2 ranged from poor (Peer Problems) to good (Hyperactivity-Inattention), respectively. Test–retest reliability range (T1-T2) was 0.65-0.78 for males and 0.71-0.86 for females.
Conclusions: The findings support the validity of the Danish SDQ-S. Only three of the subscales showed good internal consistency. Acceptable test-retest reliability was found only for two scales among males and females, respectively. Results suggest caution in using SDQ-S among vulnerable youth.