Table 1.
Independent variables used in multiple linear regression with PDD as response variable
| Variable | Value | Definition | Comment |
|---|---|---|---|
| Age | ≥18 years | n/a | Age was used as a continuous variable |
| Sex | 0= female, 1= male | n/a | |
| Drug holiday | 0= no, 1= yes | Gap between observations for a patient in the PDR that exceeds 90 days (ie, the grace period, associated with the common maximum prescription length in Sweden) | |
| Expedition year | Starting year: 2006 | ||
| ADHD diagnosisa | Disturbance of activity and attention (F90.0); DAMP (F90.0A); ADHD (F90.0B); activity and attention disturbance (F90.0C); activity and attention disturbance, unspecified (F90.0X); hyperkinetic conduct disorders (F90.1); other hyperkinetic disorders (F90.8); ADHD, unspecified type (F90.9); other specified emotional disorders with an onset in childhood or adolescence (F98.8) | Presence of diagnosis code in the NPR | All patients will, by definition, have at least one of the diagnoses |
| Region | Stockholm, west Sweden, south Sweden, mid-Sweden, north Sweden | Region where the patient lived during the study period | |
| Comorbiditya | Autism (F84.0); atypical autism (F84.9); anxiety (F41.2–F41.9); Asperger syndrome (F84.5); bipolar disorder (F31.0–F31.9); depression (F33.0–F33.9); eating disorders (F50.8–F50.9); impulse control disorders (F63.8–F63.9); personality disorders (F60.0–F60.9); oppositional defiant disorders (F91.3); schizophrenia (F20.0–F23.2); substance use disorders (F10.2–F19.2) | Presence of any defined comorbidity | |
| Add-on ADHD medicationb | 0= no, 1= yes | Has received any other ADHD medication during the time period of OROS-MPH use | Amphetamine (N06BA01); dexamphetamine (N06BA02); atomoxetine (N06BA09); methylphenidate (OROS-MPH, MPH-IR, MPH-MR; N06BA04); modafinil (N06BA07) |
| Concomitant medicationsb | Antidepressants (N06AA02, N06AA04, N06AA06, N06AA09, N06AA10, N06AA21); antipsychotics (N05A-); anxiolytics (N05BA-, N05BB-); hypnotics (N05CC-, N05CD-, N05CF-, N05CH01); SSRIs (N06AB03, N06AB04, N06AB05, N06AB06, N06AB08, N06AB10); SNRIs (N06AX16, N06AX21); other (N06AX02, N06AX03, N06AX06, N06AX11, N06AX12, NO6AX18, NO6AX22) | Presence of any defined concomitant medication |
Notes:
Defined by code from International Statistical Classification of Diseases and Related Health Problems, Tenth Revision.13
Defined by codes from anatomic therapeutic chemical classification system.31
Abbreviations: ADHD, attention-deficit/hyperactivity disorder; DAMP, deficits in attention, motor control, and perception; MPH-IR, immediate-release methylphenidate; MPH-MR, modified-release methylphenidate; n/a, not applicable; NPR, National Patient Register; OROS-MPH, osmotic release oral system methylphenidate; PDD, dispensed patient daily dose; PDR, Prescribed Drug Register; SNRI, serotonin–norepinephrine reuptake inhibitor; SSRI, selective serotonin reuptake inhibitor.