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Prevalence and medication rates of ADHD vary geographically, both between and within countries. No absolute cutoff exists between ADHD and normal behavior, making clinician attitudes (leading to local practice cultures) a potential explanation for the observed variation in diagnosis and medication rates. The objective of this study was to describe variation in attitudes toward diagnosis and medication of ADHD among clinicians working in child and adolescent mental health services (CAMHS). We hypothesized that attitudes would vary along a spectrum from “restrictive” to “liberal”. We also explored whether differences in attitudes between clinicians were related to professional background and workplace (clinic). A survey in the form of a web-based questionnaire was developed. All CAMHS outpatient clinics in Norway were invited. Potential respondents were all clinicians involved in diagnosing and treating children and adolescents with ADHD. To investigate the existence of attitudes toward diagnosis and medication as latent constructs, we applied confirmatory factor analysis (CFA). We further examined how much of variance in attitudes could be ascribed to profession and clinics by estimating intraclass correlation coefficients. In total, 674 respondents representing 77 (88%) of the clinics participated. We confirmed variation in attitudes with average responses leaning toward the “restrictive” end of the spectrum. CFA supported “attitude toward diagnosis” and “attitude toward medication” as separate, and moderately correlated (r = 0.4) latent variables, representing a scale from restrictive to liberal. Professional background and workplace explained only a small part of variance in these attitudes.

Rates of ADHD diagnosis vary across regions in many countries. However, no prior study has investigated how much within-country geographic variation in ADHD diagnoses is explained by variation in ADHD symptom levels. We examine whether ADHD symptom levels explain variation in ADHD diagnoses among children and adolescents using nationwide survey and register data in Norway. Geographical variation in incidence of ADHD diagnosis was measured using Norwegian registry data from the child and adolescent mental health services for 2011–2016. Geographical variation in ADHD symptom levels in clinics’ catchment areas was measured using data from the Norwegian mother, father and child cohort study for 2011–2016 (n = 39,850). Cross-sectional associations between ADHD symptom levels and the incidence of ADHD diagnoses were assessed with fractional response models. Geographical variation in ADHD diagnosis rates is much larger than what can be explained by geographical variation in ADHD symptoms levels. Treatment in the Norwegian child and adolescent mental health services is free, universally available upon referral, and practically without competition from the private sector. Factors beyond health care access and unequal symptom levels seem responsible for the geographical variation in ADHD diagnosis.

IntroductionAttention-deficit/hyperactivity disorder (ADHD) is among the most common mental disorders in children and adolescents, and it is a strong risk factor for several adverse psychosocial outcomes over the lifespan. There are large between-country and within-country variations in diagnosis and medication rates. Due to ethical and practical considerations, a few studies have examined the effects of receiving a diagnosis, and there is a lack of research on effects of medication on long-term outcomes.Our project has four aims organised in four work packages: (WP1) To examine the prognosis of ADHD (with and without medication) compared with patients with other psychiatric diagnoses, patients in contact with public sector child and adolescent psychiatric outpatient clinics (without diagnosis) and the general population; (WP2) Examine within-country variation in ADHD diagnoses and medication rates by clinics’ catchment area; and(WP3) Identify causal effects of being diagnosed with ADHD and (WP4) ADHD medication on long-term outcomes.Method and analysisOur project links several nationwide Norwegian registries. The patient sample is all persons aged 5–18 years that were in contact with public sector child and adolescent psychiatric outpatient clinics in 2009–2011. Our comparative analysis of prognosis will be based on survival analysis and mixed-effects models. Our analysis of variation will apply mixed-effects models and generalised linear models. We have two identification strategies for the effect of being diagnosed with ADHD and of receiving medication on long-term outcomes. Both strategies rely on using preference-based instrumental variables, which in our project are based on provider preferences for ADHD diagnosis and medication.Ethics and disseminationThe project is approved by the Regional Ethics Committee, Norway (REC number 2017/2150/REC south-east D). All papers will be published in open-access journals and results will be presented in national and international conferences.Trial registration numbersISRCTN11573246 and ISRCTN11891971.

Objective - Preference-based instrumental variables (PP IV) designs can identify causal effects when patients receive treatment due to variation in providers’ treatment preference. We offer a systematic review and methodological assessment of PP IV applications in health research. Study Design and Setting - We included studies that applied PP IV for evaluation of any treatment in any population in health research (PROSPERO: CRD42020165014). We searched within four databases (Medline, Web of Science, ScienceDirect, SpringerLink) and four journals (including full-text and title and abstract sources) between January 1, 1998, and March 5, 2020. We extracted data on areas of applications and methodology, including assumptions using Swanson and Hernan's (2013) guideline. Results - We included 185 of 1087 identified studies. The use of PP IV has increased, being predominantly used for treatment effects in cancer, cardiovascular disease, and mental health. The most common PP IV was treatment variation at the facility-level, followed by physician- and regional-level. Only 12 percent of applications report the four main assumptions for PP IV. Selection on treatment may be a potential issue in 46 percent of studies. Conclusion - The assumptions of PP IV are not sufficiently reported in existing work. PP IV-studies should use reporting guidelines.