The behavioral, mood, and biological characteristics of mental disorders often overlap and occur comorbidly. Attention deficit hyperactivity disorder (ADHD) and autism spectrum disorder (ASD) are the most difficult developmental disorders to distinguish from each other (American Psychiatric Association [APA], 2013). ADHD is a neurodevelopmental disorder characterized by inattention, hyperactivity, and impulsivity, and one or more symptoms often manifest during childhood (American Psychiatric Association [APA], 2013). The prevalence of ADHD is between 5.0 and 7.2% in children (Willcutt, 2012; American Psychiatric Association [APA], 2013; Thomas et al., 2015). ASD is also a neurodevelopmental disorder, with a prevalence of approximately 1.0%, and it is characterized by persistent deficits in social communication and interaction across multiple contexts, and restricted, repetitive patterns of behavior, interests, or activity (American Psychiatric Association [APA], 2013).

Although the main characteristics of ADHD and ASD differ, the two disorders overlap partially. For example, high rates of ADHD and ASD comorbidity have been reported (Yoshida and Uchiyama, 2004), and individuals with ADHD often exhibit interpersonal communication issues similar to those in observed in individuals with ASD (Nijmeijer et al., 2009). In addition, people with ASD sometimes present with impulsivity and inattention, which are characteristics of ADHD (Nicolson and Castellanos, 2000). Moreover, neuroimaging studies have shown that the two disorders share abnormalities in the inferior parietal lobe (Brieber et al., 2007) and precuneus (Di Martino et al., 2013). Although diagnostic agreement between physicians and psychotherapists is important because treatments differ between ADHD and ASD (Perry, 1998), psychological assessment is difficult, and several studies have indicated that inaccurate diagnoses constitute a serious problem (Mayou and Hawton, 1986; Ruggero et al., 2010; Matson and Kozlowski, 2011). Further, because ADHD and ASD symptoms overlap, detection and differential diagnosis are difficult for these disorders. For example, a study conducted by Miodovnik et al. (2015), with a study sample that included predominantly (i.e., 80–90%) White or Black children, found that 20% of those diagnosed with ASD had initially been diagnosed with ADHD. Therefore, the researchers posited that an incorrect diagnosis of ADHD could delay the diagnosis of ASD.

Interestingly, the prevalence of ADHD and ASD provided in the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5; American Psychiatric Association [APA], 2013) are inconsistent with those reported by the National Institute of Special Needs Education, Japan (NISE). The National Institute of Special Needs Education Japan [NISE] (2015) reported that the number of students with ASD who required special needs education was higher than the number of students with ADHD. In addition, 42.4% of the 174,881 elementary or junior high students who enrolled in classes for special needs education registered based on ASD or emotional disturbances. Moreover, 12,308 students with ASD received special needs services in resource rooms, which provide education to children with special needs in a regular classroom. In contrast, no special needs education classes were provided for students with ADHD, and 10,324 of these students received special needs services in resource rooms. Furthermore, Getahun et al. (2013) showed a possible cultural difference in increasing tendencies to diagnose ADHD, suggesting that the number of Asian/Pacific Island children diagnosed with ADHD remained unchanged over time (approximately 1 per 100 children), while the numbers of Black, Hispanic, and White children diagnosed with ADHD increased significantly between 2001 and 2010. The reason for the high ASD prevalence in Japan could be that children with ADHD who also met the criteria for ASD were diagnosed with ASD, rather than ADHD, before the DSM-5 was published. However, this inconsistency is questionable, because these diagnostic criteria are the same internationally. One possible explanation for this finding is that physicians’ or psychotherapists’ cultural backgrounds underlie the higher ASD rates and lower ADHD rates. Some researchers have attempted to elucidate biomarkers for ADHD, as the use of the subjective approach involves risk of under- or over-diagnosis of ADHD symptoms (e.g., Zhu et al., 2008; Monden et al., 2015). Therefore, consideration of the aforementioned inconsistencies should include subjectivity in diagnosis and factors that affect subjectivity, such as cultural differences.

Daley (2002) noted that illness awareness and concepts are affected by what behavior is noticed first and whether it is perceived as problematic. Furthermore, as Ravindran and Myers (2012) noted in their review, culture plays an important and distinct role in perceptions of health, illness, and disability; for example, there are varied and widespread perceptions of disability among cultures and the definition of a “handicap” depends on cultural context. Mann et al. (1992) provide a key example: They asked mental health professionals from four countries to examine 8-year-old boys’ behavior using videotaped vignettes and found that Chinese and Indonesian clinicians gave significantly higher scores for hyperactive-disruptive behaviors than did Japanese and American clinicians. They suggested that this result reflected a difference in cultural standards for appropriate child behaviors; for example, emotional control and conformity in preschool in China, permissiveness and student self-regulation with little direct teacher discipline during lower school grades in Japan, and individual expression and creativity in United States. These observations led to the idea that, although ADHD diagnoses have become more globalized and the attitude, diagnoses, and treatment have changed in the past decades (Conrad and Bergey, 2014), cultural differences still affect assessment (Mason et al., 2014).

Studies examining developmental disorders have been conducted mainly in Western cultures (Sun and Allison, 2010). However, prevalence rates are affected by the circumstances present in each country. For example, the ASD prevalence in China (i.e., approximately 10 per 10,000 population) is lower relative to those in Western countries (Sun and Allison, 2010). One of the reasons for this difference could be that developmental disorders are not widely understood in China, as preschool teachers’ lack of knowledge regarding ASD (Liu et al., 2016) is problematic. In contrast, levels of familiarity with developmental disorders are high in Japan (Takahara and Tsuda, 2012). Therefore, other factors could explain why the ASD rate is higher, relative to the ADHD rate, in non-Western cultural contexts where developmental disorders are well known, such as Japan.

Heuristics constitute a key factor affecting clinical judgment, as they play a vital role in the reasoning process (Vázquez-Costa and Costa-Alcaraz, 2013). Humans cannot process all the information that they are exposed to because time and cognitive resources are limited. Heuristics allow for rapid decision-making, but could also lead to cognitive error in clinical judgment. For example, “premature closure” refers to the tendency to accept a potential diagnosis and end the decision-making process prematurely; social and cultural contexts could influence this mental shortcut. Takahara and Tsuda (2012) examined familiarity with terms related to developmental disorders in the general population, with responses provided using four-point Likert scales (1 = I do not know the term, 2 = I have heard the term, 3 = I know something about the term, and 4 = I know the term well). According to the results, the proportion of people who were familiar with ADHD was higher than 20% (including I know something about the term and I know the term well), while over 60% of people were familiar with ASD (however, rates for Asperger’s syndrome, high-functioning autism, and pervasive developmental disorder were low). The most general sources of information included newspapers and television, indicating that there were numerous opportunities to obtain information concerning ASD in everyday life. Furthermore, Asian people characteristically attach high value to non-verbal information (Hall, 1976; Ishii et al., 2003), and difficulty with non-verbal skills is one of the main characteristics of ASD. Fundamental research has shown that a high degree of familiarity with stimuli affects psychological processes, including those involving perception or cognitive function such as rapid visual search or low-threshold perception (Howes and Solomon, 1951; Wang et al., 1994). Therefore, it is possible that Japanese people adopt information regarding highly familiar ASD-related characteristics.

Based on these findings, the amount of attention paid to ASD could be greater relative to that paid to ADHD in Japan, which is contrary to tendencies observed in the West. However, little is known regarding attitudes toward ADHD and ASD in non-Western cultural contexts. Characterizing how ADHD and ASD are recognized could enhance current understanding and identify factors leading to inappropriate diagnosis and assessment. This could help to identify future directions in the development of psychology assessment methods suitable for use with people of diverse ethnicities. The objective of this study was to examine the characteristics of the assessment attitude toward ADHD among Japanese clinical professionals and to discuss them in a cultural context. The aim of Study 1 was to examine participants’ recognition of ADHD, relative to that of ASD. The aim of Study 2 was to determine whether clinicians’ biases were reflected in the assessment of fictional cases, based on the results of Study 1.

The results of the study showed inconsistencies and biases in understanding regarding ADHD and ASD in individuals who performed psychological assessments in the Japanese population. Almost half of the participants in Study 1 understood that ADHD and ASD are distinct disorders; however, the remaining participants did not. In addition, participants in Study 1 focused more strongly on ASD relative to ADHD. Moreover, based on the results of Study 2, mental health professionals could exhibit a tendency toward confusing DSED with ASD.

The service climate, with respect to medicine, education, and welfare, in each country should be considered when discussing biases in assessment and diagnosis. To diagnose children with ASD is not considered to provide greater benefits than diagnosing other mental health disorders, including ADHD, in Japan, as children with any type of mental health disorder are almost equally eligible to receive welfare, medical, and educational services; mental disability certificates for the provision of financial aid; pharmacotherapy; and social skills training. However, despite this equality in the service climate, we conclude that the attitudes of medical doctors and other professionals could be biased toward ASD, as the participants’ focus on ASD-related characteristics was stronger than that on ADHD- and DSED-related characteristics in both experiments.

The rating of child hyperactive-disruptive behaviors by mental health professionals differs per culture (Mann et al., 1992); therefore, distinct cultures have diverse social norms regarding valuable behavior. For example, harmony and cohesiveness in the group is valuable in non-Western cultures; in contrast, Western cultures emphasize autonomy (Chen and French, 2008). These distinct values may affect children’s education and development (Chen and French, 2008), which would also influence assessment tendencies in clinicians.

Matson et al. (2011, 2017) examined children’s autism as rated by parents, guardians, caretakers, or teachers in Israel, South Korea, the United Kingdom, and the United States (Matson et al., 2011) and in Greece, Italy, Japan, Poland, and the United States (Matson et al., 2017). Their multinational comparisons consistently showed that ratings made by participants differed among multinational groups. They found that item endorsement frequencies for the “Verbal Communication” subscale were consistently the highest for children from the United States and Poland, whereas there was greater variation for the “Repetitive Behaviors/Restricted Interest” subscale (Matson et al., 2017). On the “Socialization/Non-verbal Communication” subscale, there was some variation across items. Interestingly, the children from Japan had the highest rate compared with other countries for the items, “Understanding age appropriate jokes, figures of speech, or sayings,” “Use of too few or too many social gestures,” and “Intellectual abilities,” even though children from the United States and Poland generally had higher endorsement frequency for these items. This is consistent with our result that participants focused on children’s social interactions. The current results indicate that the behavior aspect of individuals with ASD, which are sometimes considered as deficits, for example with regards to interaction with others, are seen as more valuable than other psychological characteristics in group-oriented social contexts.

Some studies of psychological assessment have noted the impact of cultural differences via internationalization. Main concerns included how children’s ethnic diversity affects mental health professionals and/or teachers’ decisions regarding participants’ behavior (e.g., Reid et al., 1998), how mental health professionals and/or teachers’ cultural differences affect their decisions regarding participants’ behavior (e.g., Mann et al., 1992; Matson et al., 2011), and the interaction between raters and children’s ethnicity (de Ramírez and Shapiro, 2005). For example, Reid et al. (1998) found that teachers’ ratings of ADHD for African-American children were significantly higher than those for white children. They noted that teachers’ negative cognitive bias for a specific ethnicity could be caused by the halo effect, which led to high ratings of ADHD. Mann et al. (1992) found that perceptions of hyperactivity vary significantly across raters’ countries, even if uniform rating criteria are applied. The current study indicates that future research should also focus on the clinician’s cultural background to determine if it affects clinical decision-making regarding disease identification.

Regarding bias in assessment, Bruchmüller et al. (2012) found that therapists exhibited a bias toward diagnosing ADHD in boys rather than girls. According to the current results and those of Bruchmüller et al. (2012), mental health professionals require training to reduce the influence of their own biases. However, this could be problematic, as therapists could find it difficult to avoid the influence of multiple factors, such as their own personalities or cultural contexts, leading to errors in assessment. As mentioned in the Introduction, heuristics, which constitute one of the factors affecting clinical judgment, play a key role in the reasoning process (Vázquez-Costa and Costa-Alcaraz, 2013). Identifying and understanding the characteristics of heuristics and implementing strategies, such as metacognitive training and recognition of difficulties in diagnosis, are critical to avoid this type of cognitive error (Vázquez-Costa and Costa-Alcaraz, 2013). In addition, the results indicate that bias based on cultural background in doctors and therapists could affect their clinical judgment.

When therapists assess children’s psychiatric traits, they usually use multiple assessment methods and test batteries (e.g., observation, questionnaires, clinical interviews with caregivers or teachers, psychological and neuropsychological tests, and electroencephalography). When assessing ASD or ADHD, diagnostic schedules and questionnaires (e.g., the Autism Diagnostic Interview-Revised [Le Couteur et al., 1989], Diagnostic Interview for Social and Communication Disorders, [Wing et al., 2002], Autism Spectrum Screening Questionnaire [Ehlers et al., 1999], and ADHD Rating Scale-IV [DuPaul et al., 1998]) are vital tools that are used to collect and share information, particularly that regarding children. However, these assessment tools do not consider therapist bias. The development of assessment strategies is urgently required to support professionals in overcoming their own biases. In addition to ensuring that therapists listen to clients’ descriptions of their symptoms and measure these symptoms thoroughly, efforts to address therapists’ tendency to focus on the detection of specific characteristics (e.g., rating therapists’ tendency to focus on ASD-related traits, as clients’ ASD scores could be affected by therapists’ biases) could improve assessment accuracy.

The current study was subject to some limitations. For example, the sample size was small, perhaps because few professionals and professional medical organizations are able to diagnose or assess developmental disorders (The Administrative Evaluation Bureau, 2017), and we limited participants’ occupational categories based on our interests (i.e., mental health professionals). Therefore, there were very few qualified individuals in the specialized agencies invited to participate in the study. In addition, the small sample size prevented the comparison of occupational categories. Further, we used only one vignette per diagnosis in Study 2; therefore, future studies should use experimental designs that include multiple trials (i.e., vignettes) for each diagnosis. Moreover, the survey included only Japanese professionals. Therefore, the results are not generalizable to other non-Western cultural contexts or directly comparable to Western cultures.

Despite these limitations, the results indicated that doctors’ and psychological therapists’ cultural backgrounds affected their assessments. It is necessary to examine these issues in other countries, because cultural or regional differences in prevalence and increases in the incidence of mental health problems have been observed (Matson and Kozlowski, 2011; Getahun et al., 2013) and could depend on various biases, and it is possible that other mental health issues reflect distinct cultural contexts. Furthermore, as this cultural effect on clinical judgment might occur for other psychological disorders in addition to ADHD and ASD, it is important that cultural effect of relevance to each disorder are investigated. Finally, as Japanese individuals frequently communicate elliptically, while Western individuals express themselves clearly (Ray, 1998), to understand the former requires the ability to “take a hint” or “read between the lines” during communication. Understanding Japanese individual’s intentions is relatively difficult, as subjective well-being is closely associated with interdependence and interpersonal engagement in Japan, but with the frequency of interpersonally disengaged positive emotions (e.g., pride) in the United States (Kitayama et al., 2000). Moreover, because Asian people characteristically attach high value to non-verbal information (Hall, 1976; Ishii et al., 2003), it is possible that a given individual’s unusual behavior would be attributed to non-verbal issues. The current results suggest that the knowledge of cultural differences in communication style or social norms could contribute to the understanding of clinical diagnoses.

After careful consideration, we have concluded that our survey study does not require an ethical review. There are two main reasons for this conclusion. First, the content of the study has been approved by the respective developmental support field agencies. Participants were invited from specialized agencies in the developmental support field (hospitals, elementary schools, child consultation centers, and Support Center for Developmental Disorders). Each agency was informed about the purpose of the research, voluntary nature of participation, and anonymity of the responses collected. The agencies could inform its constituents. Therefore, participants were recruited only if the agency confirmed that the study was appropriate for its constituents. Second, the same details were provided to the participants. Before participants answered the questionnaire, we set opportunities at different times for agencies or participants to choose whether they wanted to join the study. In addition, participants were allowed to quit answering the questionnaire anytime they wanted. Although our study has not been approved by the research ethics committee, we believe that the voluntary participation and effort of participants is significant. Therefore, our study complies with the ethical policy of your journal.

MM, SK, and MN: Study conception or design, interpretation of study data, drafting the manuscript or revising it for critical intellectual content, final approval of the version to be published, and agreement to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. MM: acquisition and analysis.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.