This 3-wave longitudinal study (12 months, 6-month intervals) evaluated the psychometric properties of the 9-item Social Media Disorder Scale (SMD) in 306 Greek early adolescents (mean age 13.3 years, 42.8% boys), including measurement invariance, item-level precision via IRT, and validity against depressive symptoms and health behaviors.
The SMD's unidimensional structure held across all 3 waves with full scalar invariance (ΔSRMR = 0.007). Peak measurement precision was at moderate severity (θ = 1, ~4 criteria endorsed). Higher problematic SMU at Wave 1 predicted lower daytime alertness (OR = 0.70), less physical activity (β = –0.22), and nearly double energy drink consumption (IRR = 1.98) one year later. Cross-sectional correlations with depressive symptoms were strong (r = 0.65–0.74 across waves).
- Convenience sample from one Greek prefecture limits generalizability. - Modest sample size (n = 306) introduces some uncertainty in IRT parameter estimates, especially at extreme latent trait levels. - Single-item measures for health behaviors and self-report only; no parental or objective data.
The Greek SMD works reliably as a repeated screening tool for problematic social media use in early adolescents, particularly for identifying those at moderate risk (~4 of 9 criteria). Clinicians and school health staff can use it with confidence that scores reflect real change over time, not measurement drift.
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