ADHD has an estimated prevalence of 3% to 6% Prevalence and Correlates of ADHD Symptoms in the National Health Interview Survey

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1 / Journal Cuffe et of al. Attention / ADHD Disorders Symptoms / in November the NHIS2005 Prevalence and Correlates of ADHD Symptoms in the National Health Interview Survey Journal of Attention Disorders Volume 9 Number 2 November Sage Publications / hosted at Steven P. Cuffe Charity G. Moore Robert E. McKeown University of South Carolina Objective: Study the prevalence and correlates of ADHD symptoms in the National Health Interview Survey (NHIS). Methods: NHIS includes 10,367 children ages 4 to 17. Parents report lifetime diagnosis of ADHD and complete the Strengths and Difficulties Questionnaire (SDQ). Prevalences of clinically significant ADHD and comorbid symptoms by race and ethnicity, gender, and age are presented. Results: Prevalence of clinically significant SDQ ADHD symptoms is 4.19% (males) and 1.77% (females). Male prevalence by race is 3.06% for Hispanics, 4.33% for Whites, and 5.65% for Blacks. Significant differences in prevalence occur across gender (p <.01) and among males across race (p <.01), age (p <.01), and income (p <.02). In the full sample, 6.80% of males and 2.50% of females have a parent-reported lifetime ADHD diagnosis but are negative for SDQ ADHD. Likewise, 1.59% of males and 0.81% of females are positive for SDQ ADHD but negative for parent report of ADHD diagnosis. SDQ ADHD positive children have substantially higher proportions of elevated scores on other SDQ subscales. Conclusion: ADHD symptoms vary by race and ethnicity, gender, and age and are associated with other emotional and behavioral difficulties. Both overdiagnosis and underdiagnosis of ADHD may be issues in the U.S. population of 4- to 17- year-olds. (J. of Att. Dis. 2005;9(2), ) Keywords: ADHD; prevalence; race; comorbidity ADHD has an estimated prevalence of 3% to 6% (American Psychiatric Association, 1994; Goldman, Genel, Bexman, & Slanetz, 1998; National Institutes of Health, 2000). However, estimates of the community prevalence of ADHD vary widely depending on the study methodology, diagnostic criteria used, and the population studied (Cantwell, 1996; Goldman et al., 1998). Prevalence estimates have ranged from 1.5% to 19.9% (Barbaresi et al., 2002; Baumgaertel, Wolraich, & Dietrich, 1995; Breton et al., 1999; Cuffe et al., 2001; Goldman et al., 1998; Gomez, Harvey, Quick, Scharer, & Harris, 1999; Nolan, Gadow, & Sprafkin, 2001; Szatmari, Offord, & Boyle, 1989; Wolraich, Hannah, Pinnock, Baumgaertel, & Brown, 1996). There is consensus that the change from the Diagnostic and Statistical Manual of Mental Disorders (3rd ed., revised; American Psychiatric Association, 1987) to Diagnostic and Statistical Manual of Mental Disorders (4th ed.; American Psychiatric Association, 1994) increased the prevalence of ADHD (Baumgaertel et al., 1995; Goldman et al., 1998; Lahey et al., 1994; Wolraich et al., 1996). The change in criteria results in the inclusion of significantly more children diagnosed with the primarily inattentive subtype of ADHD (more females and preschoolers). For example, in one study (Wolraich et al., 1996), the prevalence of ADHD using DSM-III-R was 7.3%, whereas it was 11.4% when applying DSM-IV criteria (more than a 50% increase in prevalence). The maleto-female ratio of ADHD diagnosis is roughly 4:1 in community samples (Cantwell, 1996). Girls tend to have the primarily inattentive subtype, with one study reporting 92% of the girls with ADHD receiving this diagnosis (Weiler, Bellinger, Marmor, Rancier, & Waber, 1999). Uncertainty remains concerning the true community prevalence of ADHD. ADHD carries a high psychosocial burden because of its impact on quality of life for affected children and their families; demands on educational resources; behavioral sequelae, including risk behaviors; and the complications of comorbid conditions. Learning disabilities (LD) are found in 20% to 40% of children with ADHD. Barkley (1998, p. 101) summarized the LD literature and reports 392

2 Cuffe et al. / ADHD Symptoms in the NHIS 393 that 8% to 39% of children with ADHD have a reading disability, 12% to 30% a math disability, and 12% to 27% a spelling disability. Children with ADHD are more likely to repeat a grade, be expelled, and drop out of school (Barkley, 1998; Weiss & Hechtman, 1993). They have more physical injuries and a higher incidence of automobile accidents (Barkley, Murphy, & Kwasnik, 1996; DiScala, Lescohier, Barthel, & Li, 1998). Children with ADHD develop into adults who are more likely to have poor occupational functioning, antisocial behaviors, and drug or alcohol abuse (Mannuzza, Klein, Bessler, Malloy, & LaPadula, 1993; Weiss & Hechtman, 1993). Comorbidity of ADHD with affective, anxiety, and conduct disorders is well established. Up to two thirds of children with ADHD have at least one other psychiatric diagnosis (Cantwell, 1996). Szatmari et al. (1989) report that about 40% of their community sample of children with ADHD had a diagnosis of conduct disorder and that rates for emotional disorders ranged from a low of 16.7% in 4- to 11-year-old girls to 50% in 12- to 16-year-old girls. Goldman et al. (1998) report the overall prevalence of diagnoses in ADHD samples is 20% for conduct disorder, up to 40% for oppositional defiant disorder, and 10% to 20% for mood disorders. Cuffe et al. (2001) found affective disorders significantly associated with ADHD in adolescents. Perceptions of hyperactivity also vary significantly across cultures (Gingerich, Turnock, Litfin, & Rosen, 1998; Mann et al., 1992). There is a major gap in the literature regarding epidemiology and services research on ADHD in Blacks (Samuel et al., 1997; Samuel et al., 1999). The current literature on racial and ethnic differences in psychiatric disorders derives mainly from behavior and symptom checklist data. There is evidence of possible differences by race and ethnicity in the prevalence of psychiatric disorders in general and ADHD in particular. Bird (1996) reports cross-cultural differences of psychiatric symptoms. He identifies two reports showing that overall Child Behavior Checklist scores were higher in the United States than in Puerto Rico or the Netherlands. There is also suggestion in the literature that Hispanic children might have a lower prevalence of ADHD (Dominguez de Ramirez & Shapiro, 1998). In addition, in the Methods for the Epidemiology of Child and Adolescent Mental Disorders study, the prevalence of ADHD varied dramatically across sites despite the fact that they all used the same methodology. ADHD prevalence ranged from a low of 1.6% in the largely Hispanic Puerto Rico site to a high of 9.4% in the Atlanta, Georgia, site (Jensen et al., 1999). American Indian children had a lower rate of ADHD in the Great Smoky Mountains Study, but the difference was not statistically significant (Costella, Farmer, Angold, Burns, & Erkanli, 1997). On the other hand, there are several studies reporting that Black children had higher rates of ADHD symptoms than White children (DuPaul et al., 1998; Epstein, March, Conners, & Jackson, 1998; Nolan et al., 2001; Reid, Casat, Norton, Anastopoulos, & Temple, 2001; Reid et al., 1998). However, in a study examining the 1998 National Health Interview Survey, White parents more frequently reported they were told by a health care professional that their child had ADHD (Lesesne, Visser, & White, 2003). The number and severity of ADHD symptoms declines with age, thus reducing the prevalence of ADHD in adolescents and adults. However, as with other age groups, the prevalence of clinically significant ADHD in adolescents remains unclear. Some studies report a dramatic decline in ADHD prevalence in adolescents and adults (Hill & Schoener, 1996; Mannuzza, Klein, Bessler, Malloy, & LaPadula, 1998), whereas others show a relatively high prevalence in adults. Murphy and Barkley (1996) found that 4.7% of a sample of licensed drivers had ADHD. Community samples of adolescents report prevalence estimates between 1.5% and 6% (Cohen, Cohen, & Brook, 1993; Cuffe et al., 2001; Fergusson, Horwood, & Lynskey, 1993; Verhulst, van der Ende, Ferdinand, & Kasius, 1997). The extent of the decline in diagnosis of ADHD in adolescence requires further research. The current study uses data from the 2001 National Health Interview Survey (National Center for Health Statistics, 2002), a large, nationally representative sample including more than 10,000 children between the ages of 4 and 17. Prevalence of ADHD from parent-reported ADHD symptoms is compared by gender, race, age, and socioeconomic status. Based on the current literature, hypotheses to be tested include the following: (a) Males will have a higher prevalence than females; (b) there will be differences by race, with Hispanics having lower prevalence and Blacks having higher prevalence than Whites; (c) adolescents will have a lower prevalence than younger children; and (d) there will be high comorbidity for affective and anxiety problems, learning problems, and conduct problems. Population Studied Method Data were drawn from the National Health Interview Survey (NHIS) Sample Child Component for The

3 394 Journal of Attention Disorders / November 2005 NHIS (National Center for Health Statistics, 2002) is conducted annually by the National Center for Health Statistics (NCHS), Centers for Disease Control and Prevention, and is representative of the civilian, noninstitutionalized, household population of the United States. This study is a secondary analysis of data collected in the survey. As part of the NHIS, one sample child (younger than age 18) is randomly selected from each family participating in the survey. Information on each child is collected with the Sample Child Core questionnaires. The 2001 Sample Child file (n = 13,579) contains basic information on health status, health care services, and behavior. The information was obtained from a knowledgeable adult (18 years of age or older), typically a parent or guardian, residing in the household. The analysis was limited to children 4 years of age or older and those without mental retardation, Down s syndrome, and autism. The final sample size was 10,255 representing 56.1 million U.S. civilian, noninstitutionalized children. In the 2001 NHIS, as a part of a collaborative agreement with the National Institute of Mental Health, the Strengths and Difficulties Questionnaire (SDQ) was added as a supplement on children s mental health. The SDQ replaced the Child Behavior Checklist by Achenbach and Edelbrock for children ages 4 to 17. The SDQ has been used in place of the Child Behavior Checklist because it is shorter and comparable in performance. The SDQ is a brief behavioral screening questionnaire for children ages 4 to 17, with extended questions that provide information on the duration of a child s problem and the impact that problem has on the child and his or her family. Three versions are available for use: the parent, teacher, and child self-report versions. The NHIS used the parent report SDQ. The first part of the SDQ consists of 25 scale items scored 0 (not true), 1 (somewhat true), or 2 (definitely true). These items can be divided into five subscales, each from 5 items measuring the following psychological attributes or dimensions: (a) emotional symptoms, (b) conduct problems, (c) hyperactive behavior, (d) peer relationships, and (e) prosocial behavior. The second part of the SDQ obtains additional information about the duration and impact of symptoms. The SDQ is a valid and reliable instrument, with five subscales associated with psychiatric disorders (Goodman, 2001). Internal consistency is satisfactory, with Cronbach s α coefficient mean of.73. Retest was performed after 4 to 6 months, so a true idea of retest reliability is not available (Goodman, 2001). However, even after such a long interval, the mean reliability was.62. All subscales are associated with relevant, independently determined psychiatric diagnoses. Overall, the odds ratio for having a psychiatric disorder if a child scored in the clinically significant range on any SDQ subscale based on parent report is In general, specificity and negative predictive value are high, and sensitivity and positive predictive value are relatively lower. For the parent report SDQ, the hyperactivity subscale has an odds ratio of 32.3 (95% confidence interval, 23.8 to 43.9), a specificity of 92%, and a sensitivity of 74% for an ADHD diagnosis (Goodman, 2001). Independent Variables We used the NHIS codes for race and ethnicity, which define children as Hispanic or non-hispanic White, Black, or Other. The Other category comprises primarily Asian and American Indian children. Age was categorized into three levels: 4 to 8, 9 to 13, and 14 to 17. Family income was assessed by a variable provided by NHIS that indicates if the family s income is more than or less than $20,000. Parental education was defined by the highest level of education obtained by a parent in the household. The variable was recoded as having high school education or higher or having less than a high school education. All analyses were stratified by gender. Outcomes: ADHD via SDQ or Parent Report ADHD was determined by the SDQ using the following criteria: a. Hyperactivity behavior score 7 (five items scored 0 = not true, 1=somewhat true, or2=definitely true, listed below) 1. Restless, overactive, cannot stay still for long 2. Constantly fidgeting or squirming 3. Easily distracted, concentration wanders 4. Thinks things out before acting (reversed score) 5. Sees task through to the end, good attention span (reversed score) b. Difficulties in emotions, concentration, behavior, or being able to get along with other people being present longer than 6 months c. The difficulties interfere with the child s everyday life in at least two of the following areas: home life, friendships, classroom learning, and leisure activities. Responses are scored as follows: 0 = not at all,0=a little,1=a medium amount, and 2 = a great deal. (Please note: the published SDQ criteria only require an impairment score of 2 or more so that impairment could occur in only one of these domains if it were severe enough.

4 Cuffe et al. / ADHD Symptoms in the NHIS 395 This study modified the requirement to at least moderate difficulty in two domains to be more consistent with the DSM-IV criteria). The question pertaining to parent-reported ADHD diagnosis is as follows: Has a doctor or health professional ever told you that [child s name] had ADHD or ADD? Learning disabilities were ascertained with a single question on the Sample Child Core Questionnaire: Has a representative from a school or a health professional ever told you that your child has a learning disability? The responses to both questions are yes, no, refused, and don t know. Comorbidities Each child s SDQ scores on the remaining four subscales of the SDQ were dichotomized into abnormal or normal to provide information on the prevalence of comorbidity among children with SDQ-derived ADHD symptoms. The cut points for each of the scales were as follows: emotional problems 5, conduct problems 4, peer relationships 4, and prosocial behavior 4. Statistical Analysis NHIS data are collected using a complex sample design involving multistage sampling, clustering, and stratification. We used SAS Version 8.02 for all data management and SAS Callable SUDAAN Release for our analysis to account for the weighting and study design and to obtain correct variance estimation. We used the statements recommended by NCHS for SUDAAN procedures. NHIS documentation does not state a minimum number of observations necessary for an estimate to be considered statistically reliable. Standard errors are presented with all proportions to facilitate evaluation of the reliability of the estimates. A standard error larger than 30% of the estimate indicates that the estimate should be interpreted with caution. These are italicized in the tables. Chi-square analyses were used to compare rates of ADHD across levels of factors of interest. We used multiple logistic regression to assess the effects of several characteristics of the adolescent and the household in which he or she lived. The model contained measures of race and ethnicity, age, sex, location of residence, family income, and highest education of a parent in the household. Chisquare tests were performed at α =.05 level. Multiple logistic regression results are presented with odds ratios (OR) and 95% confidence intervals (CI) for each level of each factor. Table 1 Demographics and Weighted Percentages of the 2001 NHIS Sample Males Females (unweighted n = 5,248; (unweighted n = 5,007; weighted n = 28,652,207) weighted n = 27,494,036) % SE % SE Race Hispanic White Black Other Age 4 to to to Family income Greater than $20,000 Less than $20,000 Highest level of education in household High school or more Less than high school Location of residence MSA Non-MSA Note: NHIS = National Health Interview Survey; MSA = metropolitan statistical area. Results Demographics of the sample are presented in Table 1. All percentages are weighted. The sample is approximately 51% male, 64% White, 16% Hispanic, 15% Black, and 5% Other. Adolescents ages 14 to 17 make up a slightly smaller percentage of the sample (28%) than do the two younger age groups (34% to 38%). Almost 17% had family incomes of less than $20,000, and 13% lived in a household with the highest education level attained of less than high school. Eighty percent of the children live in a metropolitan statistical area (MSA). Table 2 presents the prevalence of SDQ clinically significant ADHD symptoms by the independent variables of interest. Overall, parents reported clinically significant ADHD symptoms in 4.19% of males and 1.77% of females (chi-square test for gender difference, p <.01). In chi-square analyses, among females, there were no differ-

5 396 Journal of Attention Disorders / November 2005 Table 2 Prevalence of Clinically Significant SDQ ADHD Symptoms by Sex and Demographic Characteristics Males Females % SE % SE Elevated SDQ ADHD score total Race Hispanic White Black Other Age 4 to to to Family income Greater than $20, Less than $20, Highest level of education High school or more Less than high school Location of residence MSA Non-MSA Source: National Center for Health Statistics (2002). Note: SDQ = Strengths and Difficulties Questionnaire. A standard error larger than 30% of the estimate indicates that the estimate should be interpreted with caution. These are italicized. ences by race, age, income, level of education, or residence. Among males, Hispanic children had significantly fewer SDQ ADHD symptoms than Black children (p =.04). Both White and Black children had significantly more SDQ ADHD symptoms than children from the Other category (p <.001). Prevalence in Hispanic males was 3.06%, compared with 4.33% in White and 5.65% in Black males. Although Blacks had a higher prevalence of ADHD, the difference was not statistically significant in comparison to Whites. Male children ages 9 to 13 were more likely than either older or younger male children to have significant ADHD symptoms (p <.01). Family income was also associated with having SDQ ADHD symptoms in males (p =.02). Table 3 compares parent reports of a lifetime history of an ADHD diagnosis with current (past 6 months) SDQderived ADHD. In the total population, 6.8% of males and 2.5% of females had a parent-reported diagnosis of ADHD in the absence of a positive SDQ. On the other hand, 1.59% of males and 0.81% of females were positive for SDQ ADHD in the absence of a parent-reported history of an ADHD diagnosis. Thus, 38% of males and 46% Table 3 Parent Report of ADHD Diagnosis (Lifetime) and SDQ ADHD Status by Sex Males Females % SE % SE Among those SDQ positive Parent report of diagnosis of ADHD and ADD Among those SDQ negative Parent report of diagnosis of ADHD and ADD Among those with parent report of ADHD and ADD diagnosis SDQ positive Among those without parent report of ADHD and ADD diagnosis SDQ positive Classification of parent report and SDQ ADHD Both SDQ and parent report diagnosis Parent-reported diagnosis only SDQ only Neither Note: SDQ = Strengths and Difficulties Questionnaire. of females with clinically significant SDQ ADHD had not been diagnosed in the past. Among those negative for SDQ ADHD, children with a parent report of ADHD diagnosis were significantly older (mean age of for males and for females) than children with no parent-reported history of ADHD (10.34 for males and for females). This suggests the possibility that some of the discrepancies between a positive history of ADHD and a negative SDQ is accounted for by adolescents with a history of ADHD who no longer meet SDQ ADHD criteria. There is no significant age difference between the SDQ ADHD positive children whose parent reported ADHD diagnosis compared to those with no parent-reported diagnosis. The latter may represent a group of previously undiagnosed children with ADHD. Comorbidity between SDQ ADHD and other SDQ subscales and areas of impairment are presented in Table 4. Children with clinically significant SDQ ADHD symptoms have higher rates of problems in all the other subscales of the SDQ. Roughly 65% of the children with SDQ ADHD also have conduct problems. More females than males with SDQ ADHD have emotional problems (56.76% and 41.92%, respectively, p =.05) and learning disabilities (50.73% and 45.20%, respectively, ns). Of

6 Cuffe et al. / ADHD Symptoms in the NHIS 397 Table 4 Proportion of Clinically Significant Elevation of Other SDQ Subscales and Impairment by Sex and SDQ ADHD Status Males Females % SE % SE Comorbidity among SDQ positive Emotional Conduct Peer Low prosocial Learning disabilities Comorbidity among SDQ negative Emotional Conduct Peer Low prosocial Learning disabilities Impairment among SDQ positive Home Friends Class Leisure Source: National Center for Health Statistics (2002). Note: SDQ = Strengths and Difficulties Questionnaire. children with SDQ ADHD, 84.7% have elevated scores on at least one other SDQ subscale, 57.9% have at least two other elevated scores, and 34.8% have elevations on at least three other subscales. High levels of impairment are seen across all domains in the SDQ. Impairment in the classroom is reported in almost 94% of children with SDQ ADHD. Impairment in the home setting is the next most common at 82.23% in males and 73.43% in females. More than 60% were reported to have problems with friends, and about half had impairment in leisure activities. Multivariable logistic regression analysis is presented in Table 5. Males are significantly more likely than females to have ADHD (OR = 2.55; 95% CI 1.83 to 3.55). When controlling for other independent variables and using the White group as the referent group, the odds ratio for Hispanic children is 0.6 (CI 0.38 to 0.94). Hispanic children are at significantly lower risk of having SDQderived ADHD than White children. Black children do not significantly differ from Whites in these data. The middle age group (9 to 13) is more likely to have ADHD, as are children from families with household incomes of less than $20,000. Urban versus rural environment is not associated with ADHD in this sample. Table 5 Multiple Logistic Regression Modeling on SDQ ADHD Discussion Odds Ratio 95% Confidence Interval Gender Male , 3.55 Female 1.00 Race and ethnicity Hispanic , 0.94 Non-Hispanic White 1.00 Non-Hispanic Black , 1.64 Non-Hispanic Other , 1.38 Location of residence Non-MSA , 1.74 MSA 1.00 Age 4 to , to , to Family income Greater than $20, , 0.94 Less than $20, Highest level of education in household High school or more , 1.29 Less than high school 1.00 Note: SDQ - Strengths and Difficulties Questionnaire; MSA = metropolitan statistical area. The prevalence of probable ADHD by the SDQ is similar to the reported prevalence of ADHD in other epidemiological studies but lower than some more recent studies. These data suggest, however, that there may be differences in prevalence of ADHD by race in addition to gender and age. Hispanic children and children from the Other race category had lower levels of reported ADHD symptoms on the SDQ. The Other category is made up primarily of various Asian ethnicities and American Indian and Pacific Islander children. The data suggest these disparate groups may also have a lower risk of ADHD, but the numbers are too small for further analysis, rendering the findings less useful for understanding the prevalence of ADHD for children within these race and ethnic groups. Further study of children from these backgrounds is indicated. In the multiple logistic regression analyses, Hispanic children were significantly less likely to have an ADHD SDQ diagnosis compared to White children. To our knowledge, this is the first study using a validated instrument and a national sample of children to show ethnic differences in the prevalence of ADHD. The prevalence of clinically significant ADHD symptoms in

7 398 Journal of Attention Disorders / November 2005 Caucasian children was 40% higher than in Hispanic children. This difference appears to be both statistically and clinically significant. Consistent with previous literature, Black children had higher prevalence of SDQ ADHD than White children, although the difference was not statistically significant in these data. The possibility of racial bias by an informant of another race is removed in this study, as the diagnosis is based solely on reports of a knowledgeable adult in the household, most often a parent. However, use of only one informant is also a relative weakness of the study. Further work on racial and ethnic differences should include reports from teachers and children. It is possible that the current findings result from cultural differences in reporting by parents rather than actual differences in ADHD symptoms or impairment. Should such reporting differences exist, they could attenuate real differences in prevalence or create the appearance of greater differences than actually exist. Issues of possible culturally based differences in tolerance of behavioral symptoms or differing thresholds for reporting problem behaviors should be further studied. The prevalence of ADHD in this study is affected by at least two factors. First, there is an 8% false positive rate and a 26% false negative rate with the SDQ (Goodman, 2001). The false positives may account for some of the group of children positive for SDQ ADHD but whose parent did not report a diagnosis. However, it is likely that many children in this group are as yet undetected and undiagnosed with ADHD. In addition, our group used a slightly different algorithm for defining SDQ ADHD. This study required a parent report of impairment in two settings, as is the standard in DSM-IV. Using the published SDQ algorithm, which does not require two areas of impairments, would include 1.44% more males and 0.58% more females from this sample. The change in algorithm likely reduces the number of children identified by the SDQ as having ADHD who actually do not have the disorder (false positives), although the number of false negative scores may be higher. Up to 26% of children with ADHD in the sample may screen negative for ADHD by the SDQ. Second, there may be some children with parent-reported ADHD who are treated and thus have fewer symptoms and a negative SDQ. This would cause a lower prevalence of ADHD in this sample. Thus, it is likely that the prevalence of ADHD in this study is a conservative estimate. The lay press and media have recently been concerned with possible overdiagnosis of children with ADHD. These data do not lend themselves well to the study of overdiagnosis, as the parent report of a history of ADHD is lifetime compared to the SDQ report of symptoms in the past 6 months. However, the number of children with parent-reported history of ADHD and negative ADHD by SDQ is by far the largest group of children (6.8% of males and 2.5% of females) with a presumptive ADHD diagnosis. This is consistent with the view that overdiagnosis of ADHD in the community may be a problem. However, many of these children may be false negatives from the SDQ, treated and thus no longer meeting ADHD criteria, or older children who no longer meet full criteria for ADHD. There has been little or no discussion in the media of possible underdiagnosis of ADHD. The fact that 38% of males and 46% of females with clinically significant ADHD as identified by the SDQ had no history of a prior ADHD diagnosis suggests that underdiagnosis of ADHD is a problem. This appears to be significantly higher than would be expected based on the 8% false positive rate of the SDQ. Professionals identifying, diagnosing, and treating children with ADHD need to be aware of the possible underdiagnosis issue. In particular, school-based and primary care professionals need to be more aware of this potential problem. These data show that ADHD is associated with a high rate of impairment across multiple domains of functioning. In addition, consistent with the extant literature, the children identified in this study also show high rates of comorbid emotional, conduct, and learning problems. Clearly, the children are in need of further assessment and appropriate treatment. Socioeconomic status is also associated with ADHD symptoms in this study. This has been inconsistently found in the prior literature (see Barkley, 1998, pp ). Because there is a strong genetic component to ADHD, parents of children with ADHD are more likely to have had ADHD themselves and to have lower levels of education, occupational achievement, and income as a result. Likewise, the previous literature on urban-rural differences in prevalence of ADHD is inconsistent. This study found no significant differences based on urban versus rural environment. Despite the fact that SDQ is a screening instrument that does not result in an actual diagnosis of ADHD, the level of comorbid problems in the SDQ ADHD positive group is comparable to that found in previous epidemiological research. These children have multiple areas of functional impairment. Conduct problems, emotional problems, and learning disabilities are all highly prevalent, with almost 85% of these children having clinically significant scores on at least one other SDQ subscale. In addition, parents of

8 Cuffe et al. / ADHD Symptoms in the NHIS 399 SDQ ADHD children report that 94% are impaired in the classroom and 75% to 80% are impaired in the home. The children with clinically significant SDQ ADHD symptoms are impaired in multiple domains. Limitations The major limitation of this study concerns the use of the SDQ because it does not contain all 18 items of DSM- IV ADHD criteria. Although in previous research the SDQ has been shown to have reasonable psychometric properties, it does have the problem of false positive and false negative misclassification of children with ADHD. This limits the confidence one can hold in the results of the study. Further study of diverse racial and ethnic populations is necessary prior to concluding definitively that the prevalence of ADHD varies in different racial and ethnic groups. However, the problem of misclassification should not vary by cultural group, making it more likely that the relative differences in prevalence of ADHD would remain in a study with a more standard ADHD assessment. Additionally, because of small numbers in cells for smaller ethnic populations, this study can only shed light on the three largest racial and ethnic populations in the United States. Further research is needed in the American Indian and Asian populations to determine ADHD prevalence in these groups. As mentioned, the use of a single informant for ADHD symptoms is another limitation of these data. Clinical Implications ADHD is a significant problem in the United States, and the prevalence varies by age, gender, and race and ethnicity in this study. Although there may be problems with overdiagnosis of ADHD, clinicians, teachers, and other professionals should also be aware of the possible underdiagnosis of ADHD. More females than males had SDQ ADHD and no prior history of ADHD diagnosis. If ADHD is undetected in 38% to 46% of children with ADHD, then the underdiagnosis of ADHD is a significant problem. Past research has identified the primarily inattentive subtype as the one most likely to be undetected, and these children are also more likely to have learning disabilities. Clinicians should be aware of this when assessing children with school-related problems. Clinicians consulting with schools should also educate teachers, parents, and guidance counselors about this problem so that these children can be identified and treated. In conclusion, further research is warranted concerning the prevalence of ADHD across race and ethnicity. Is this finding a result of differences in the reporting of symptoms by parents in different ethnic, racial, or cultural groups, or is it reflective of a difference in the actual prevalence of ADHD? What role does the issue of bias among caregivers and teachers play in our view of ADHD across racial and ethnic groups? The population of the United States continues to change and grow more diverse. People of Hispanic descent now make up the largest minority group in the United States, and immigrants from many Asian countries continue to make their way to the United States. Understanding the basis for and implications of the ethnic differences observed in this study is essential for effective intervention and treatment programs. In addition, if teachers, physicians, parents, and other caregivers are better informed about the symptoms of ADHD across age, race, and gender, then the dual problems of underdiagnosis and overdiagnosis should likewise be improved. References American Psychiatric Association. (1987). Diagnostic and statistical manual of mental disorders (3rd ed., revised). Washington, DC: Author. American Psychiatric Association. (1994). 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L., Hannah, J. N., Pinnock, T. Y., Baumgaertel, A., & Brown, J. (1996). Comparison of diagnostic criteria for attentiondeficit hyperactivity disorder in a county-wide sample. Journal of the American Academy of Child and Adolescent Psychiatry, 35, Steven P. Cuffe, M.D., is HPI Professor of Neuropsychiatry and Behavioral Science and Director, Division of Child and Adolescent Psychiatry at the University of South Carolina School of Medicine. He

10 Cuffe et al. / ADHD Symptoms in the NHIS 401 is a Fellow of the American Academy of Child and Adolescent Psychiatry. His areas of research interest include ADHD, PTSD, epidemiology, and substance use disorders. Current research projects include a school-based study of ADHD in 4-to-10-year-old children and the association of affective and anxiety disorders in children with diabetes. Robert McKeown is Professor and Associate Dean for Research in the Arnold School of Public Health, University of South Carolina. He is a Fellow of the American College of Epidemiology and member of its Board of Directors. His research interests are psychiatric epidemiology, perinatal epidemiology, and public health ethics. His teaching has focused on epidemiologic methods, ethics, and psychiatric epidemiology, with recent publications in the latter two areas. Charity G. Moore, Ph.D., MSPH, is a research assistant professor in the departments of medicine and biostatistics at the University of North Carolina (UNC). She is also a Research Fellow at the Cecil G. Sheps Center for Health Services Research at UNC. Currently, she serves as the lead biostatistician for the Clinical Research Scholars Program at UNC. She also collaborates in research on rural health services and evaluation of chronic disease interventions.