Youth Experiences and Health (YEAH) Study - Psychological Symptoms and Resources as Predictors of Mental Health Among Treatment-seeking Adolescents

The current research will identify specific self-reported risk symptoms for psychosis and psychiatric hospitalization. Data will be collected in a large (N=1000) intake sample from the adolescent outpatients units of three Finnish university hospitals. Besides the central psychotic-like experiences, psychosocial protective factors of positive mental health, resilience, and social networks will also be simultaneously assessed, as well as potentiating risk factors such as trauma, sleep disorders, affective symptoms, borderline personality traits, and substance use. The predictive value of psychotic-like experiences, in isolation and in interaction with the other measures, will assessed with an inclusive national register follow-up of psychosis diagnoses and all-causes psychiatric hospitalization. The study will thus produce risk algorithms for everyday use in psychiatric care. For immediate applicability of results, tools for computerized self-report and automatic risk calculation will be made available for clinical use.

ANALYSIS PLAN To ensure a strong foundation for the primary predictor of positive psychotic-like experience (PLE) intensity, the structural validity of the YEAH questionnaire will be assessed with a theory-driven confirmatory bifactor model, taking into account the ordinal nature of items. In the case of unsatisfactory fit, exploratory analyses will be performed.

The main pre-planned outcome analysis will be baseline latent positive and negative PLE levels on the YEAH questionaire and their interaction predicting the follow-up transition to psychosis. Secondary analyses using the same predictors will use all-causes hospitalization as the outcome, as an indicator of a general deterioration of mental health. Exploratory LASSO analyses of the same outcomes will include as additional predictors all baseline assessments of psychosocial health and symptoms, as well as the symptom stability in the questionnaire follow-up. Best analysis and reporting practices recommended for the field will be followed (Studerus et al, 2017), to minimize chance findings and to allow accurate replication.

Power analyses The expected minimum sample size of 900 questionnaires is conservative for the planned main analyses. In our previous Helsinki Prodromal Study with a similar sampling strategy (Therman et al., 2014), 3.5% of respondents were diagnosed with psychosis within one year. With the consequently expected group sizes of 31 (psychosis) and 869 (others) and error probabilities α and β conservatively both set at 5%, a sensitivity analysis for a one-tailed t-test indicates a required effect size of 0.60 (Cohen's d) for the outcome-group difference in PLE intensity, which is the worst-case scenario. In our previous study, the d for the total score on the fairly non-specific Prodromal Questionnaire was 0.50, and the effect sizes for the brief questionnaires in the Kline et al. (2015) and Kobayashi et al. (2008) studies all corresponded to a d of 1.1 or greater. A d of 0.90 is a thus a conservative expectation with the new questionnaire, which would require a sample size of only 420. With a cut-off set to 20% test positives, already this effect size would achieve clinical usefulness as an initial screen, when the two-year psychosis rate is 5% (sensitivity 50%, positive predictive value 13%, diagnostic odds ratio 4.4). With a realistically obtainable d of 1.5 as the best-case scenario, the questionnaire screening would under the same conditions be highly useful (sensitivity 71%, positive predictive value 18%, diagnostic odds ratio 12).

DOCUMENTATION AND QUALITY Possibilities for continued use of the data will be ensured by carefully documenting data collection methods, external circumstances, as well as the contents of the dataset. For documentation, the project will use the Data Documentation Initiative (DDI, version 3.2 with lifecycle support) international metadata standard.