Impact of children's language ability on self-report assessment of mental health: Testing measurement invariance using moderated non-linear factor analysis.

Children with language difficulties are at elevated risk of mental health problems, yet tools commonly used to assess mental health rely heavily on language. It is unclear if children's language ability influences their self-report measures. We tested language-related measurement invariance using moderated non-linear factor analyses. We used self-report data from children (10-11 years) with a wide range of language abilities, living in the UK, on the Revised Child Anxiety and Depression Scale-25 (RCADS-25; n = 342; 171 female; 80 with language difficulties) and the Strengths and Difficulties Questionnaire-Youth Report (SDQ-YR; n = 349; 174 female; 84 with language difficulties). Language-related differences were identified in both measures: six RCADS-25 items and three SDQ-YR items functioned differently in relation to language ability. For the RCADS-25, these differences did not affect anxiety and depression factor means. For the SDQ-YR, language-related item differences did affect peer problems and prosocial factor means, but not emotional problems, conduct problems, or hyperactivity. RCADS-25 factor scores appear robust for children with language difficulties, though item responses should be interpreted cautiously. In contrast, language-related differences in the SDQ-YR may limit comparisons of peer problems and prosocial subscales across children with differing language abilities.