Procedure and participants
The present study included data of 230 participants (females: n = 103, 44.8%; males: n = 127, 55.2%) with a mean age of 34.63 years (SD = 11.88; range = 17–65 years) and an average IQ of 107.88 (SD = 14.37; range = 83–145). Data were collected from a sample of adults from our ADHD outpatient consultation department for clarification of possible ADHD diagnosis (n = 136, 59.1%) as well as further participants (without suspicion of ADHD diagnosis) recruited on personal demand by the authors (n = 94, 40.9%). Study procedures were performed in accordance with the ethical standards of the Declaration of Helsinki. Participants were informed about study procedures and goals, voluntary participation, as well as anonymization of data. Written consent was provided.
Questionnaires
ADHD self-rating questionnaire (ADHS-SB). Current ADHD symptomatology was assessed by the ADHD-SB, a self-rating questionnaire affiliated to the Homburger ADHD scales for adults (Rösler et al. 2008). The presence of a total of 22 items (18 symptom and four additional information items) is to be rated on a four-point Likert scale from 0 (= not present) to 3 (= severe). Item scores can be summed up to the three subscales Inattention (items 1–9), Hyperactivity (items 10–14), and Impulsivity (items 15–18). Moreover, a total current ADHD score can be calculated by adding up all 18 symptom items. Total current ADHD scores equal or above the cut-off value of 15 indicate clinically relevant current ADHD symptomatology.
Good psychometric properties were proven for the ADHD-SB, e.g., with test–retest reliabilities between r = 0.78 and 0.89 as well as internal consistencies between Cronbach’s α = 0.72 and 0.90 (Rösler et al. 2004). The total current ADHD score cut-off value of 15 showed a 77% sensitivity and a 75% specificity (Rösler et al. 2008).
Wender Utah Rating Scale-short version (WURS-k). Childhood ADHD was assessed by the WURS-k, another self-rating questionnaire affiliated to the Homburger ADHD scales for adults (Retz-Junginger et al. 2002; Rösler et al. 2008). For the retrospective estimation of ADHD symptoms within the age of 8–10 years, their presence is to be rated on 25 items (21 symptom items and four control items) using a five-point Likert scale from 0 (= not present) to 4 (= severe). The 21 symptom items are summed up to a total childhood ADHD score. Total childhood ADHD scores equal or above the cut-off value of 30 indicate clinically relevant childhood ADHD symptomatology.
Good psychometric properties were proven for the WURS-k, e.g., with a test–retest reliability of r = 0.90 (Rösler et al. 2008) and an internal consistency of Cronbach’s α = 0.91 (Stieglitz 2000). The total childhood ADHD score cut-off value of 30 showed a 85–93% sensitivity and a 76–92% specificity (Retz-Junginger et al. 2003, 2007).
Stress coping questionnaire (SVF). The German stress coping questionnaire (“Stressverarbeitungsfragebogen”, SVF; Janke et al. 1985) was used to describe cognitive and behavioral strategies aimed at maintaining or re-arranging psychological/psychosomatic stability after experiences of distress. Thereby, not only adaptive (short- and long-term stress-reducing) but also maladaptive (short-term stress-reducing but long-term stress-enhancing) strategies were assessed. The 114-item version of the SVF was used in the present study. Each participant was asked for his/her general tendency to react in terms of the given item when he/she feels impaired, negatively aroused, or imbalanced by someone scored on five-point Likert scale from 0 (= not at all) to 4 (= very likely). Items can be arranged to 19 subscales, representing (a) adaptive coping strategies (minimization, self-aggrandizement by comparison with others, denial of guild, distraction, substitute gratification, search for self-affirmation, situation control, reaction control, positive self-instructions, and need for social support), and (b) maladaptive coping strategies (avoidance, escape, social withdrawal, rumination, resignation, self-pity, self-blame, aggression, and drug use) (e.g., Ising et al. 2006). For the present study, we used t scores as provided by the manual, which were based on a German, non-clinical norm sample of 96 male and 104 female adults.
Good psychometric properties were proven for the SVF, e.g., with internal consistencies for most subscales of Cronbach’s α ≥ 0.79, except drug use with Cronbach’s α = 0.61 (Janke et al. 1985).
Sheehan disability scales. Participants rated the severity of current self-perceived impairments within the fields of work/school, social life, and family life/home responsibilities on the Sheehan Disability Scales (Sheehan 1983). Scores ranging from 0 to 10 can be clustered for each domain to represent no impairments (= 0), mild impairments (= 1–3), moderate impairments (= 4–6), severe impairments (= 7–9), and extreme impairments (= 10). Moreover, a total impairment score can be calculated by summing up ratings of all three scales.
Concerning psychometric properties, scales have been successfully implemented for reliable and valid assessment of functional impairments in ADHD patients (Coles et al. 2014; Pawaskar et al. 2020).
Symptom checklist 90-R (SCL-90-R). The German version of the SCL-90-R (Derogatis 1977; Franke and Derogatis 2002) was used to assess further (comorbid) psychological distress. Self-reports about the occurrence and severity of respective symptoms within the preceding 7 days are provided on 90 items that are scored on a five-point Likert scale ranging from 0 (= not at all) to 4 (= very strongly). Items can be assigned to nine subscales (somatization, obsessive compulsion, interpersonal sensitivity, depression, anxiety, hostility, phobic anxiety, paranoid ideation, and psychoticism). The global severity index (GSI) represents an average score across all items and, thus, serves as an indicator for overall self-perceived psychological distress. For the present study, we used t value transformations of subscale scores (Franke 1992) as well as the GSI.
Good psychometric properties were proven for the German SCL-90-R, e.g., with internal consistencies between Cronbach’s α = 0.79 and 0.98 (Franke et al. 1992).
Multiple-choice vocabulary intelligence test (MWT-B). To account for possible confounding due to general cognitive capability, participants took a short intelligence test in the form of the MWT-B (“Mehrfachwahl-Wortschatztest”; Lehrl 1977). This test measures verbal (crystallized) intelligence as an indicator of general cognitive capability, because it has been claimed not to be as susceptible to bias by psychological/psychiatric disturbances as fluid intelligence. Participants are given a sheet with a total of 37 lines, each of which containing five combinations of letters with only one displaying an actual word of the German language. This word must be identified. Based on the sum of correctly identified words, IQ values can be assigned according to the manual.
The MWT-B, which is commonly applied as German screening measure for cognitive capability, has been successfully implemented in ADHD research that has pointed to good psychometric properties, e.g., in terms of construct validity and test–retest reliability (r = 0.90; e.g., Conzelmann et al. 2010).
Statistical analyses
Data were processed in IBM SPSS version 26.0. To investigate descriptive group differences between ADHD and non-ADHD participants, we conducted χ2-statistics for categorical variables (e.g., sex, clustered Sheehan Disability Scale ratings) and, for linear variables, t tests (e.g., age, IQ) as well as MANOVAs with post hoc Bonferroni or Games–Howell tests (SVF, SCL-90-R and linear Sheehan Disability Scale ratings) respecting potential interdependencies among variables. Partial eta-squared (\(\eta_{{\text{p}}}^{2}\)) was used as effect size to represent the percentage of variance in the dependent variable explained a the independent variable with values of 0.01, 0.06, and 0.14 representing small, medium, and large effects, respectively (Cohen 1988). For the examination of predictive effects of ADHD symptomatology on (1) the use of stress coping strategies, and (2) life impairments, as well as (3) potential buffering or intensifying effects of stress coping strategies on the associations between ADHD and life impairments irrespective of age, sex, and IQ, we performed multiple linear regression analyses (forced entry). First, we included the ADHD-SB scores as independent and the SVF subscale scores as dependent variables, with age, sex, and IQ as control variables (Table 4). Second (Tables 5, 6, online supplements), we used the ADHD-SB scores as independent and the linear Sheehan Disability Scale scores as dependent variable in a basic model (controlled for age, sex, and IQ), and then tested remaining predictive effects when further independent variables such as SVF subscale scores (Model a), SVF subscale and SCL-90-R GSI scores (Model b), and SVF subscale, SCL-90-R GSI scores, and the interaction term of ADHD-SB and SVF subscale scores were simultaneously considered. Accounting for α-error inflation due to multiple testing, we only considered findings with p values ≤ 0.001 as meaningful.