Intelligence, socioeconomic status, and gender impact ADHD diagnosis timing

A new study published in the British Journal of Clinical Psychology has shed light on how individual characteristics and demographic factors may affect the timing of ADHD diagnoses. Using data from a large sample of children in Ontario, researchers found that children with higher intelligence scores, certain symptom types, and higher socioeconomic backgrounds were more likely to be diagnosed with ADHD at a later age. Additionally, non-White maternal ethnicity also correlated with delayed diagnosis, underscoring possible disparities in the diagnostic process.

Attention-deficit/hyperactivity disorder, or ADHD, is a neurodevelopmental condition characterized by persistent patterns of inattention, hyperactivity, and impulsivity that interfere with daily functioning. Individuals with ADHD may struggle to stay focused, complete tasks, or control impulsive actions, which can lead to challenges in academic, social, and personal contexts. The symptoms of ADHD typically appear in childhood, often before the age of 12, and can continue into adolescence and adulthood, affecting a person’s performance in school, work, and relationships.

The researchers undertook this study to address concerns around the underdiagnosis of ADHD in specific groups, particularly girls and individuals with high cognitive abilities. ADHD is a neurodevelopmental condition that has historically been more commonly diagnosed in boys, which can lead to an oversight of girls with the condition.

Past research suggested that girls often present ADHD symptoms differently, tending toward inattention and internalized symptoms rather than the more disruptive behaviors frequently seen in boys. These differences could mask ADHD symptoms, especially in high-functioning girls, leading to a delayed or missed diagnosis. The new study aimed to understand whether cognitive ability and symptom type influence diagnosis age and to examine if other factors, like socioeconomic background and ethnicity, also contribute to disparities.

The researchers used data from the Province of Ontario Neurodevelopmental Disorders Network, which includes information on 1,380 children diagnosed with ADHD. For their analysis, they selected 568 children who had completed the required assessments. Their methods included two main analyses: first, they looked at whether the child’s sex and cognitive ability predicted the age at which they were diagnosed, and second, they examined how specific ADHD symptoms and demographic details influenced diagnosis timing.

The children’s cognitive abilities were assessed using standardized intelligence tests, while ADHD symptoms were measured with the Strengths and Weaknesses of ADHD Symptoms and Normal Behaviors scale. Demographic factors included family income, caregiver education, and the ethnicity of both the child and parents.

The study’s findings highlighted a significant relationship between intelligence scores and age of diagnosis. Children with higher IQ scores were diagnosed later than those with lower scores, which aligns with previous research indicating that children with higher cognitive abilities might be able to mask ADHD symptoms better, especially inattentive symptoms, which are less disruptive.

Notably, while the researchers expected that this effect might differ between boys and girls, they found that higher IQ scores were associated with a later diagnosis age across both sexes. However, there was no significant difference in diagnosis age between boys and girls in the sample. This may suggest that girls who eventually receive a diagnosis have more prominent symptoms that match the traditional ADHD presentation associated with boys, potentially making them more noticeable.

The researchers also observed that children who displayed more hyperactive and impulsive behaviors tended to receive earlier diagnoses. In contrast, inattentive symptoms alone did not correlate with diagnosis age, supporting the idea that disruptive behaviors are more likely to draw the attention of parents, teachers, or healthcare professionals. Internalizing symptoms, such as anxiety or depression, showed a trend toward later diagnoses, particularly in girls, but the sample size limited strong conclusions on this aspect.

The study revealed interesting links between demographic factors and the timing of ADHD diagnoses. Higher socioeconomic status, indicated by family income and parental education, was associated with later diagnoses. This finding is counterintuitive compared to some U.S.-based studies that have suggested children from lower socioeconomic backgrounds are diagnosed later due to access issues.

The researchers suggest that Canada’s public healthcare system, which provides more equitable access to services than the United States, might explain why higher socioeconomic status correlates with later diagnosis in this context. Higher parental education levels were also correlated with later diagnosis ages, possibly reflecting that these families are more aware of the nuanced aspects of ADHD, potentially leading to a later but more accurate diagnosis.

Additionally, maternal ethnicity played a role in diagnosis age. Children whose mothers identified as non-White tended to be diagnosed at a later age than those with White mothers. While the study’s findings did not extend this delay to the child’s own reported ethnicity, the researchers note that maternal factors, such as cultural attitudes toward ADHD and healthcare, might impact when and how parents seek a diagnosis for their children. Cross-cultural studies have shown that ADHD may be underrecognized in ethnic minority groups, leading to delays in diagnosis and treatment. This difference in recognition may relate to cultural variations in understanding ADHD symptoms or barriers in communication with healthcare providers.

While this study provides important insights, the authors note some limitations. First, the sample included only children with clinical diagnoses of ADHD, meaning it did not account for those who may have ADHD but remain undiagnosed. Including a broader sample in future studies would allow for comparisons between clinically diagnosed and undiagnosed children, particularly to explore if undiagnosed girls present high cognitive abilities or specific internalizing symptoms that mask their ADHD. Additionally, the demographic data were incomplete for some participants, which restricted analyses and may have limited the study’s power to detect effects in certain groups.

Future research could benefit from more comprehensive data on internalizing symptoms and ethnicity, as well as a focus on undiagnosed children who may exhibit ADHD traits but do not meet the full diagnostic criteria. Overall, the study emphasizes the importance of recognizing that ADHD diagnosis timing can be influenced by a child’s intelligence, behavioral presentation, and demographic context. By identifying these factors, clinicians may be better equipped to detect ADHD across a more diverse range of children, potentially reducing the negative impacts of delayed or missed diagnoses in certain groups.

The study, “Sex and intelligence quotient differences in age of diagnosis among youth with attention-deficit hyperactivity disorder,” was authored by Carolynn Hare, Alexandra C. Leslie, Lindsay P. Bodell, Erin A. Kaufman, J. Bruce Morton, Robert Nicolson, Elizabeth Kelley, Jessica Jones, Muhammed Ayub, Jennifer Crosbie, Russell Schachar, Evdokia Anagnostou, Magali Segers, and Ryan A. Stevenson.