Number of problems for each subscale (Sample 1).

Many existing measures of psychological well- and ill-being are used with young people without testing contemporary adolescent understanding of them. The purpose of this study was to use think aloud interviews to test adolescent understanding of three existing, and one newly created psychological well- or ill-being measures. An initial sample of 40 female participants aged 13–14 years took part in the study. Problematic items were identified based on thematic analysis of adolescent feedback. One item of the Lethargy Scale and one item of the Subjective Vitality Scale were adapted following integration of think aloud findings. The results also indicated that the Brief Serenity Scale was unsuitable for the participants. Subsequently, a second sample of 57 female participants aged 13–14 years completed the think aloud protocol with an alternative measure of serenity, the Child Serenity Scale, and thematic analysis revealed no items were problematic. A 24-item psychological well- and ill-being self-report measure was consequently proposed for use in future research.