Procedure

Neurotypical Control Group The assessment procedure for healthy participants was approved by the Ethical Committee Psychology (ECP) at the University of Groningen. All participants in the Control Group gave written informed consent and were subsequently asked for anamnestic information including age, sex, and educational attainment. Additionally, participants were asked about any history of psychiatric or neurological disease, as well as pharmacological treatments affecting the central nervous system. They were then instructed to complete all self-report measures (i.e., WURS-K, ASR, CAARS-ACI) honestly and to the best of their ability.

ADHD Groups Having given informed consent, adults with ADHD were tested individually in a quiet room on clinic premises. They were assured that all data collected as part of the study would be analyzed anonymously and that the results would not affect their clinical assessment or treatment. No reward was offered for participation in the research project. Patients underwent a comprehensive clinical assessment, which encompassed self-report questionnaires, standardized measures of cognition, as well as the previously described validity tests. Testing took approximately 2 h, divided into two parts to avoid potential effects of fatigue (Lezak et al. 2004). The study complied with the ethical standards of the Helsinki Declaration and was approved by the local institutional ethical committee (Medical Faculty at the University of Heidelberg, Germany).

Simulation Group Like honest-responding controls, participants allocated to the Simulation Group gave written informed consent, provided anamnestic information, and completed a validity test. In contrast to the Control Group; however, they were asked to answer the CAARS-ACI as though they had ADHD. Examiners were aware of the instructions the simulating participants received.

To help them adopt the role of an adult with ADHD, participants in this group were provided with a vignette describing multiple possible incentives for someone to simulate the disorder (e.g., financial, educational or vocational accommodations, or the prescription of stimulant medication). Volunteers were explicitly asked to feign ADHD in a realistic manner by providing believable answers (i.e., avoiding pronounced exaggeration of symptoms). This was further incentivized by introducing the chance of winning a tablet PC if they were the one participant who feigned the condition most convincingly. In actuality, the PC was awarded to a randomly chosen participant; that is, irrespective of test performance. Following the assessment, which took approximately 70 min, participants were debriefed and instructed to stop feigning the disorder. Additionally, they were asked whether they had followed the given instructions. All participants answered in the affirmative.