Predictive Validity of a Continuous Alternative to Nominal Subtypes of Attention-Deficit/Hyperactivity Disorder for DSM–V

Abstract

Three subtypes of attention-deficit/hyperactivity disorder (ADHD) based on numbers of symptoms of inattention (I) and hyperactivity-impulsivity (HI) were defined in the Diagnostic and Statistical Manual of Mental Disorders (4th ed.) to reduce heterogeneity of the disorder, but the subtypes proved to be highly unstable over time. A continuous alternative to nominal subtyping is evaluated in a longitudinal study of 129 four- to six-year-old children with ADHD and 130 comparison children. Children who met criteria for all subtypes in Year 1 continued to exhibit greater functional impairment than comparison children during Years 2 to 9. Among children with ADHD in Year 1, I and HI symptoms differentially predicted teacher-rated need for treatment and reading and mathematics achievement scores over the next 8 years in controlled analyses. Consistent with other studies, these findings suggest that the use of diagnostic modifiers specifying the numbers of I and HI symptoms could reduce heterogeneity and facilitate clinical intervention, prognosis, and research.

Notes

Note. Means and proportions and means with different subscripts differ at p < .05, not controlling concurrent psychopathology in Year 1. ADHD = attention-deficit/hyperactivity disorder; C = combined subtype; HI = predominantly hyperactive-impulsive subtype; I = predominantly inattentive subtype; ODD = oppositional defiant disorder; CD = conduct disorder.

^a In Year 1.

^b The log of family income in Year 1 was taken before statistical comparisons were made.

*p < .05. ****p < .0001.

Note. Model 1 = subtypes of attention-deficit/hyperactivity disorder (ADHD) and the comparison group are the predictors; methodologic (site and cohort) and demographic (age in Year 1, sex, race-ethnic group, total family income, and intelligence) covariates included; Model 2 = subtypes of ADHD and the comparison group are the predictors; methodologic and demographic covariates include with numbers of symptoms on concurrent mental disorders in Year 1 (oppositional defiant disorder, conduct disorder, and internalizing disorders); Model 3 = numbers of inattention and hyperactivity-impulsivity symptoms are the predictors among children who meet criteria for ADHD with impairment in at least one setting; methodologic and demographic covariates include with numbers of symptoms on concurrent mental disorders in Year 1 (oppositional defiant disorder, conduct disorder, and internalizing disorders); Model 4 = numbers of inattention and hyperactivity-impulsivity symptoms are the predictors among children who meet criteria for ADHD with impairment in at least one setting; methodologic and demographic covariates include with numbers of symptoms on concurrent mental disorders in Year 1 (oppositional defiant disorder, conduct disorder, and internalizing disorders). DSM–IV = Diagnostic and Statistical Manual of Mental Disorders (4th ed.); IRS = Impairment Rating Scale; ODD = number of symptoms of oppositional defiant disorder in Year 1; CD = number of symptoms of conduct disorder in Year 1; internalizing = total number of symptoms of depression and anxiety disorders in Year 1; ADHD-I = predominantly inattentive subtype; ADHD-HI = predominantly hyperactive-impulsive subtype; ADHD-C = combined subtype; HI = hyperactivity-impulsivity; I = inattention; CGAS = Children's Global Assessment Scale. All statistical tests compare the ADHD subtype groups to the non-ADHD comparison group.

^a Counts of symptoms; beta estimates reflect differences in effect at each greater number of symptoms.

*p < .05. **p < .01. ***p < .001. ****p < .0001.

Note. Reading and mathematics achievement scores tested with generalized linear regression. Model 1 = subtypes of attention-deficit/hyperactivity disorder (ADHD) and the comparison group are the predictors; methodologic (site and cohort) and demographic (age in Year 1, sex, race-ethnic group, total family income, and intelligence) covariates included; Model 2 = subtypes of ADHD and the comparison group are the predictors; methodologic and demographic covariates included with numbers of symptoms on concurrent mental disorders in Year 1 (oppositional defiant disorder, conduct disorder, and internalizing disorders); Model 3 = numbers of inattention and hyperactivity-impulsivity symptoms are the predictors among children who meet criteria for ADHD with impairment in at least one setting; methodologic and demographic covariates included; Model 4 = numbers of inattention and hyperactivity-impulsivity symptoms are the predictors among children who meet criteria for ADHD with impairment in at least one setting; methodologic and demographic covariates included with numbers of symptoms on concurrent mental disorders in Year 1 (oppositional defiant disorder, conduct disorder, and internalizing disorders). DSM–IV = Diagnostic and Statistical Manual of Mental Disorders (4th ed.); ODD = number of symptoms of oppositional defiant disorder in Year 1; CD = number of symptoms of conduct disorder in Year 1; internalizing = total number of symptoms of depression and anxiety disorders in Year 1; ADHD-I = predominantly inattentive subtype; ADHD-HI = predominantly hyperactive-impulsive subtype; ADHD-C = combined subtype; HI = hyperactivity-impulsivity; I = inattention. All statistical tests compare the ADHD subtype groups to the non-ADHD comparison group.

^a Counts of symptoms; beta estimates and odds ratios reflect differences in effect at each greater number of symptoms.

*p < .05. **p < .01. ***p < .001. ****p < .0001.

Note. Model 1 = subtypes of attention-deficit/hyperactivity disorder (ADHD) and the comparison group are the predictors; methodologic (site and cohort) and demographic (age in Year 1, sex, race-ethnic group, total family income, and intelligence) covariates included; Model 2 = subtypes of ADHD and the comparison group are the predictors; methodologic and demographic covariates included with numbers of symptoms of concurrent mental disorders in Year 1 (oppositional defiant disorder, conduct disorder, and internalizing disorders); Model 3 = numbers of inattention and hyperactivity-impulsivity symptoms are the predictors among children who meet criteria for ADHD with impairment in at least one setting; methodologic and demographic covariates included; Model 4 = numbers of inattention and hyperactivity-impulsivity symptoms are the predictors among children who meet criteria for ADHD with impairment in at least one setting; methodologic and demographic covariates included with numbers of symptoms of concurrent mental disorders in Year 1 (oppositional defiant disorder, conduct disorder, and internalizing disorders); DSM–IV = Diagnostic and Statistical Manual of Mental Disorders (4th ed.); ODD = number of symptoms of oppositional defiant disorder in Year 1; CD = number of symptoms of conduct disorder in Year 1; internalizing = total number of symptoms of depression and anxiety disorders in Year 1; ADHD-I = predominantly inattentive subtype; ADHD-HI = predominantly hyperactive-impulsive subtype; ADHD-C = combined subtype; I = inattention; HI = hyperactivity-impulsivity.

^a Counts of symptoms; odds ratios reflect differences in odds at each greater number of symptoms.

Note. ADHD = attention-deficit/hyperactivity disorder; CGAS = Children's Global Assessment Scale; ADHD-C = combined subtype; no differences = no differences among the three subtypes of ADHD at p < .05; ADHD-I = predominantly inattentive subtype; ADHD-HI = predominantly hyperactive-impulsive subtype; neither = no association between either the number of symptoms of inattention or the number of hyperactive-impulsive symptoms at p < .05. Subtype that is not listed did not differ at p < .05 from either of the listed subtypes.

^a Lower scores reflect greater impairment.

^b Difference between magnitudes of the associations of I and HI symptoms significant at p < .05 when concurrent psychopathology in Year 1 was controlled.