Research Protocol for the manuscript "Caught in the Scroll: Validating FoMOs-A and Exploring Its Links to Smartphone Addiction, social anxiety and Well-being in Portuguese Adolescents" translated to english

The Fear of Missing Out (FoMO) has become central to understanding adolescents’ engagement with social media and its psychological consequences. Given adolescents’ heightened sensitivity to peer belonging and approval, this study validated the Fear of Missing Out Scale for Adolescents (FoMOs-A) in a Portuguese sample and examined its associations with indicators of mental health and digital behaviour. A total of 288 adolescents (12–18 years) completed the FoMOs-A and measures of psychological well-being, social anxiety, and smartphone addiction. Competing models were tested using confirmatory factor analysis, and convergent, discriminant, and test–retest validity were examined. Results supported a robust two-factor structure—Internalising (emotional) and Externalising (behavioural), with good reliability and gender invariance. Higher FoMO scores correlated positively with smartphone addiction and social anxiety and negatively with psychological well-being. Differentiating these emotional and behavioural dimensions helps clarify whether vulnerability stems mainly from emotional distress related to social exclusion or from compulsive efforts to remain constantly connected online, offering useful guidance for more targeted screening and intervention. Overall, the findings provide strong evidence for the psychometric robustness and practical utility of the FoMOs-A among adolescents and highlight its relevance for educational, clinical, and research settings focused on digital well-being and mental-health promotion.