The increasing number of adults presenting for ADHD evaluations only magnifies the importance of conducting careful, comprehensive assessments for the disorder that yield thorough symptom and impairment profiles, accurate diagnoses, and effective treatment plans. Unfortunately, cursory evaluations that rely on clinical impressions rather than careful integration of norm-referenced data are all too common in current practice and often lead to misdiagnoses. The resulting over- or under-identification of ADHD in adults can have serious adverse consequences, including inappropriate or denied treatment, prolonged distress and dysfunction, the emergence of secondary problems, and the misuse of resources (e.g., time, energy, money).

As of this writing, there is no objective measure (blood test, brain scan, psychological test) to definitively confirm the presence or absence of ADHD, despite ongoing pursuits of such a diagnostic “holy grail.” Moreover, diagnosing the disorder in adults can be complicated by a variety of factors, including the number of medical, psychiatric, and psychosocial conditions producing symptoms that mimic ADHD, high comorbidity rates, challenges in establishing childhood onset, the lack of a clear boundary between “normal range” and elevated symptoms, and the possibility of malingering. In broad terms, a thorough and accurate diagnosis of ADHD requires both inclusion (determining whether the individual meets the DSM symptom criteria for the disorder) and exclusion (ruling out alternative explanations that might better account for ADHD-like symptoms). Thus, ensuring valid diagnoses and appropriate services requires clinicians with expertise in ADHD and related psychopathology to draw conclusions based on a comprehensive assessment process involving the integration of data collected from multiple informants, using a variety of methods, and covering different disorders, settings, and time periods.

Clinical practice guidelines from various professional organizations and experts in the field (APA, 2013; Canadian ADHD Resource Alliance [CADDRA], 2020; Gibbons et al., 2008; The National Institute for Health and Care Excellence [NICE], 2018; Ramsay, 2015; Sparrow & Erhardt, 2014; Wolraich et al., 2019) consistently recommend a comprehensive multi-informant, multi-method approach to assessing ADHD, whether in youth or adults. Gathering information from collateral informants who know the presenting adult well (e.g., a spouse or romantic partner, parent, close friend, relative, co-worker) is also recommended to supplement self-report data. An observer report can offset possible biases, limited insight, and memory/knowledge gaps as well as clarify symptom onset, pervasiveness across settings, persistence, and functional impairment. Likewise, gathering information using multiple modalities provides a more thorough and accurate picture of the individual. As per best practices, these methods include questionnaires and clinical interviews (covering presenting concerns, mental status, current functioning, medical/developmental history, family history, educational history, social history, occupational history, and psychiatric history), structured diagnostic interviews, clinical observations, review of records (e.g., report cards, job evaluations, treatment summaries), and standardized rating scales. Although not adequate for diagnosing ADHD, neurocognitive testing can be a useful supplement by aiding diagnostic judgments and providing a profile of cognitive strengths and weaknesses that informs treatment targets and strategies.

Rating scales represent an essential component of evaluating ADHD in children, adolescents, and adults. Broadband rating scales that cover a wide range of symptom domains (e.g., depression, anxiety, mania/hypomania, post-traumatic stress reactions, psychosis, substance abuse) can be useful for initial screening, differential diagnosis, and assessing possible comorbidities, but are not sufficient for confirming a diagnosis of ADHD. Some overly narrow rating scales are limited to a review of current DSM symptoms of ADHD, which can increase response bias to match pre-conceived notions about whether the person should be diagnosed.

Other rating scales, like the CAARS 2, include current DSM symptoms of ADHD in the context of a wider range of difficulties commonly experienced by adults with ADHD. Well-normed, psychometrically-sound ADHD rating scales provide an efficient, convenient way to collect and quantify the observations and impressions of multiple informants regarding the nature, patterning, frequency, and severity of core and associated features of the disorder. Importantly, they represent the best available tools for establishing when symptoms significantly exceed age- and/or gender-based expectations.

A major component in the diagnosis of ADHD is the individual’s self-reported symptoms and problems in functioning (Murphy & Schachar, 2000; Suhr et al., 2008). Although highly informative and integral to adult ADHD evaluations, the validity of self-reports can be compromised by a variety of factors including memory limitations, lack of insight, and various forms of response bias. For example, being motivated to receive an ADHD diagnosis in order to access stimulant medications or accommodations at work or school might lead an individual to exaggerate their symptoms, over-report problems (e.g., Faust et al., 1988; Lewandowski et al., 2014; Sullivan et al., 2007), or provide a general impression that things are worse than they really are. Although obtaining information from collateral informants (i.e., individuals who know the person being evaluated well) can compensate for some of the shortcomings of self-report data (Alexander & Liljequist, 2016; Barkley et al., 2006; Barkley et al., 2011; Kooij et al., 2008; Zucker et al., 2002), these observer reports are subject to many of the same limitations and response biases as self-reports (in part because they can involve reporting on behaviors that occurred in the past, that occur irregularly, or that are not directly observable; Holmbeck et al., 2008; Kolko & Kazdin, 1993; Voigt et al., 2007). Invalid reports (e.g., overreporting problems or exaggerating symptoms) can also be produced by informants who are highly motivated to secure help for the person being evaluated. In other instances, informants might conspire with the person being evaluated to misrepresent symptoms or problems so as to help them secure accommodations or medications. Rating scales that incorporate empirically derived symptom validity measures can help flag raters who may fabricate or intentionally exaggerate their symptoms to obtain an unwarranted ADHD diagnosis. In addition to being a critical component of diagnostic evaluations of ADHD, rating scales are also invaluable as repeated measures to monitor the effects of interventions.