1997 behavioral characteristics of dsm-iv adhd subtypes ina scholl - gaub, carlson

8/12/2019 1997 Behavioral Characteristics of DSM-IV ADHD Subtypes Ina Scholl - Gaub, Carlson

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Journal

of

Abnormal Child Psychology, Vol. 25, No. 2, 1997,pp. 103-111

Behavioral

Characteristics

of

DSM-IV

ADHD

Subtypes

in a School-Based Population

Miranda

Gaub1

and Caryn L.

Carlson

1,2

Received

August 8,1995; revision received February 21,1996;

accepted

February 27,

1996

From anethnically diverse sampleof2,744 school children,221attention

deficit

hyperactivity

disorder

(ADHD) [123 (4.5%) predominantly inattentive (IA), 47

(1.7%)

predominantly hy-

peractive/impulsive

(HI), and 51(1.9%) combined type (C)] were

identified

using teacher

ratings on a

Diagnostic

andStatisticalManualofMentalDisorders(4th ed.) (DSM-IV) symptom

checklist. Subjects were compared to 221 controls on teacher ratings of behavioral, academic,

and social

functioning.

Theresults revealed relatively independent areasof impairmentfor

eachdiagnostic group.

The IA

children were impaired

in all

areas,

but

were rated

as

dis-

playing

more appropriate behavior andfewerexternalizing problems than HI or C children.

The HI

group displayed externalizing

and

social problems,

but was

rated

as no

different

than controls

in

learning

or

internalizing problems.

The C

groupdemonstrated severe

and

pervasive

difficulties across domains. These findings support

the

validity

of the

DSM-IV

ADHD subtypes;

all

ADHD groups demonstrated impairment relative

to

controls,

but

show

different patternsofbehavioral characteristics.

KEY WORDS: ADHD; ADHD subtypes; behavioral characteristics; impairment; teacher ratings; ethnic

minority.

Since its inception, attention

deficit

hyperactivity

disorder

(ADHD)

has

been known

bymany

names,

such asminimal brain dysfunction, hyperkinesis,hy-

peractivity,

and

attention

deficit disorder with

(ADD/H) or without (ADD/WO) hyperactiviry. The

changing

nomenclature reflects disagreement regard-

ingthe diagnostic necessity of the three core charac-

teristics: impulsivity, inattention, and motor excess.

Various

editionsof the

DiagnosticandStatisticalMan-

ual

of

MentalDisorders (DSM) have implemented

varioussubtyping systems which cluster the three core

characteristicsin anumberofways.Thethird edition

[DSM-III; American Psychiatric Association (APA),

1The

UniversityofTexasat Austin, Austin, Texas78712.

2Addressallcorrespondence to CarynL.Carlson, Departmentof

Psychology,

Mezes 330, The University of Texas at Austin,

Austin,Texas78712.

1 3

CWl-OttW/WOMWOSllSM)

C

1997Plenum

PublishingCorporation

1980] subtyped ADHD children usingabidimensional

approach such that a child was diagnosed as ADD/H

orADD/WO.The revised third edition (DSM-III-R;

APA,1987)

implemented a unidimensional approach

which

included children with varying degrees

of hy-

peractivity under

the

diagnostic category

of

attention

deficit hyperactivitydisorder.

The fourth

edition (DSM-

IV;

APA, 1994)

has

returned

to a

bidimensionalsystem,

clustering hyperactivity and impulsivity symptoms into

one

dimension,

and

separating

it from the

inattention

dimension. Based

on

this system,

the

DSM-IVpre-

sents an ADHD diagnosis with three subtypes:

pre-

dominantly inattentive (IA), predominantly

hyperactive/impulsive

(HI),and combinedtype(C),

Children displaying symptoms of both inatten-

tion

and

hyperactivity

(i.e.,

ADD/H

and

ADHD)

un-

der the

various

DSM

systems have

consistently

demonstrated significant

difficulties

in adjustment,


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1 4

socialfunctioning,and internalizing and externalizing

behavior

(Barkley, 1990; Hinshaw, 1994; Whalen,

1989).The

pervasiveness

of

such associated

difficul-

ties has been demonstrated primarily within clinic-

referred

samples.

Although behavior problems

associated with ADHD have been explored in popu-

lation-based samples

to a

lesserextent, they have

also

been documented

(August,

Ostrander, &

Bloomquist, 1992; Szatmari,

Offord,

& Boyle,1989).

Research

has

demonstrated that children display-

ing both inattention and hyperactivity differ from

thosewhodisplay inattentionin theabsenceofmotor

excess. This latter

form

of

ADHD,

first

formallyiden-

tified

inDSM-III

as

ADD/WO,

has

been less

widely

studied.

In a

recent review

of the

ADD/WO litera-

ture, Lahey, Carlson, and Frick (in press) concluded

that, as compared to ADD/H children, ADD/WO

children are more internalizing but less antisocial, less

rejected

by

peers,

and less

externalizing.

The

DSM-IV

C and IA

subtypes were intended

to be

congruent with past diagnoses

of

ADD/H

and

ADD/WO,

respectively. However, DSM-IV diagnos-

tic

criteria deviate somewhatfrom those

of

previous

DSMversions, interms of numbersand clustersof

symptoms.Thus,

it

remains

to be

seen whether cur-

rent DSM

criteria identify

children

similar

to those

identified

in previous research.

The HIsubtype, introduced tocaptureagroup

of

childrenwhowere perceived byclinicians in the

field trials to have a clinically significant disorder

(Lahey et al., 1994), has no previous diagnostic coun-

terpart. The

validity

of the HI subtype has been ques-

tioned by those who have suggested that these

children, who were identified primarily among pre-

schoolers

in the field

trials,

may

eventually display

inattention symptoms

and

qualify

for a C

diagnosis

(Barkley,

1997).

The

DSM-IV

field trials (Lahey et al., 1994)

found

that, among clinic-referred children, the DSM-

IV ADHD subtypes showed

different

patterns of as-

sociated impairment. C and HI groups were rated as

more globally impaired than the IA group, while C

and

IA

children

had

more academic problems than

the HI group. Teachers rated C children as less

liked

and more disliked than HI children, while IA chil-

dren

did not differ

from

the

other

twosubtypeson

like

or

dislike

scores.

Apart

from

the field

trials,

descriptive informa-

tion about the DSM-IV diagnostic subtypes is scarce.

McBurnett, Pfiffner, Swanson, Ottolini, & Tamm

(1995) used parent

and

teacher ratings

on a

DSM-

III-R diagnostic checklist of 520 child referrals to an

ADHD clinic to retrospectively classify them into

DSM-IV subtypes. A comparison of the behavioral

characteristics of the three ADHD subtypes indicated

that, consistent

with

Lahey et al. (1994), HI children

were more academically successful than C or IA chil-

dren.HI

children

did not differ from C

children

on

ratings of peer dislike, but both of these groups were

more disliked than the IAgroup. In addition, both

the HI and C groups received higher ratings than the

IA group on measures of disruptive behavior.

Twostudies examined behavioral correlates

of

the DSM-IV subtypes in nonreferred

samples

(Baumgaertel, Wolraich,

&

Dietrich, 1995; Wolraich,

Hannah, Pinnock, Baumgaertel, & Brown, inpress).

Wolraich

et al. obtained teacher ratings for

8,258

children in grades K-5 in a middle Tennessee county.

An overall ADHD prevalence

rate

of 11.4% was ob-

tained, with ratesfor LA, C, and HI of 5.4%, 3.6%,

and

2.4%, respectively. Baumgaertel

et al.

(1995)

obtained teacher

ratings

for

1,077 children

in

Grades

1 to 4 inRegensburg, Germany.An overall

prevalence rate of 17% was obtained, with rates for

IA, C, and HI of 9%, 4.8%, and 3.9%, respectively.

Consistent with the results of Lahey et al. (1994)

and

McBuraet et al. (1995), the C and HI groups

displayed behavioral problems,

while the C and LA

groups

were

associated with academic problems.

Wolraichet al. also

found

the proportion of children

displaying anxiety/depression

was

lower

for the HI

(9.2%)

than

for the C

(29.3%)

or IA

(21.9%)

groups.

The goals of the present study were to enhance

the existing literature by (1) using a large-scale,

population-based sample to prevent contamination

bypossible referral bias; (2) exploring behavioral cor-

relatesof the three

DSM-IV-diagnosed subtypes

of

ADHD;

and (3)attemptingtoevaluatethe extentto

which

the current DSM-IV system identifies subtypes

comparable

to

those identified using previous diag-

nostic systems.

METHOD

Data

for the present study were obtained under

the auspices of a larger community service program

entitled

the Schoolof the Future Project.This pro-

gram, implemented by the Hogg Foundation, pro-

vides school-based mental health services

to low

income communities. Since 1990, this program

has

Gaub and

Carlson


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ADHD

Subtypes

1 5

Table I.

Demographic Characteristics

of

Population

Grade

Overall

Gender K 1 2 3 4 5

totals

Boys

Girls

Totals

255

263

518

19%

288

249

537

19%

261

235

496

18%

202

178

380

14%

218

184

402

15%

193

218

411

15%

1,417

52%

1,327

48%

2,744

100

been in effect in some elementary and secondary

schoolsin several Texas cities.Yearlyevaluations, in-

cluding

teacherratings, have been used to assess the

effectiveness ofservice deliveryin these schools.

Data were collected for allchildren for whom

parental consent

was

obtained (approximately

96%

of

eligible

children).

The 3% of

children

of unknown

or

other ethnicity were excluded, leaving

a

sample

of 2744children

in

nine elementary schools

who had

adequate

data available for the 1993-1994 school

year.Demographic characteristicsfor thesampleare

presented

in

Table

I. Children were predominantly

from low-socioeconomic-status (low-SES) back-

grounds.Basedonpaternal occupation, availablefor

30 of the sample, meanSESrating (using total la-

bor force comparisons) on the revised Duncan So-

cioeconomic Index (Stevens

&

Featherman, 1981)

was

23. The

ethnic composition

was 76%

Hispanic,

16%

African American, and 8% Caucasian.

Subjects

For

thecurrent study,221children, representing

8.0

of the total population, met the criteria for

ADHD

(via teacher reports)

and

were included

in

analyses. The 221 ADHD children were compared

to 221

non-ADHD subjects selected from among

nondiagnosedchildrenandmatchedforgender, age,

grade,and

ethnicity. Demographic characteristics

of

thegroups are reported inTable II.

Measures

Teacher evaluationsforeach subject consistedof

theTeacher's Report Form (TRF; Achenbach,1991),

a

teacher-completed DSM-IV-based diagnostic

checklist for

ADHD

and

oppositional

defiant

disor-

der (ODD), and three Likert-type scale questions re-

garding social functioning

[adapted

from

a

questionnaire developed by Dishion (1990) used in

the

DSM-IV

field

trials].

TRF.

The TRF (Achenbach, 1991) is a widely

used, standardized tool for the assessment ofchild-

hood functioning and impairmentinbehavioral and

emotional realms. All analyses used raw scores rather

than T-scores, since the latter are scaled

differently

for each gender.

SNAP-IV

(Swanson

Carlson, 1994). This diag-

nostic checklist

for

ADHD

and ODD

[Swanson,

No-

lan, and Pelham Checklist-IV and the DSM-IIIR

Disruptive Behavior Disorder Rating Scale (Pelham,

Gnagy,

Greenslade, & Milich, 1992)] consists of 26

questions thatclosely parallel

in

wording

the

diagnos-

tic

symptoms

forboth ADHD and ODD astheyap-

pear in the DSM-IV The instructions ask the teacher

toindicate, foreach question, whichof the following

fourchoices best describes

the

child:

not at

all, just

a

little,

quite

a

bit,

orvery

much.

Social

Functioning.

Three

questions, adapted

from Dishion (1990), were included to assess the

teacher's

perception of the child's level of social

functioning.

Teachers estimated

the

proportion

of the

child's peers that like/accepted, dislike/rejected,

and

ignoredhim/her based

on a

5-point Likert-type scale

ranging from

1(very

few/less than25 )

to 5

(almost

all/more

than

75 ).

Procedure

Data

were collected during April 1994

for the

1993-1994

school year. Subjects were excluded from

the original sample if their TRF

scores

had more

than eight unanswered items

totalor

more than

three

unanswereditems on anyscab.This sample was then

screened for those children who met DSM-IV

teacher

rating criteria

for the

three subtypes

of

ADHD. For diagnostic purposes, items endorsed as

very

muchwere tallied

as present

symptoms,

and


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1 6

Gaub andCarlson

Table II.

Group Demographic Characteristics

Hyperactive/

Demographic Combined Inattentive

impulsive

Controls

characteristic (n = 51) (n = 123) (n = 47) (n =221)

Age

[mean (SD)]

Gender

ratio (Male:Female)

Ethnicity

withingroup:Hispanic

African American

Caucasian

7.6years

(1.6)

2.8:1

70%

24%

6%

7.6

years (1.9)

2.3:1

79%

15%

6%

7.5

years (1.6)

4.1:1

57%

30%

13%

7.6

years (1.7)

2.6:1

77%

15%

8%

students

were assigned ADHD subtype diagnoses ac-

cording to DSM-IV criteria.

Toform a control group, a nondiagnosed child

wasmatched to each ADHD child. These nondiag-

nosed

controls (NC) were sought within the same

classroom

to

adjust

for

potential rater

differences.

If

a

nondiagnosed child (of the same gender and eth-

nicity)

was not in the ADHD child's classroom, a

match

was

chosen from

the

next classroom

(on an

alphabetical list) of the same grade within that

school.Onrare occasions, amatchhad to bechosen

from

a

same grade classroom

at a

different elemen-

taryschool. Approximately

94% of the

matches were

from the

same classroom,

5%

werefrom

a

different

classroom

in the

same school,

and

fewer than

1%

werefrom adifferent school.

Analyses

compared the three ADHD subtypes

and

the NC group on 19 variables

(four

TRF adjust-

ment

questions, eleven TRF behavior scales, three

sociometric questions,and ODD

symptom

rating).To

maintain a focus on diagnostic group, data for the

current study were collapsed across ethnicity and age.

Gender was not included as an independent variable

inthe current

study

since a separate report of gender

effects

is in preparation.

RESULTS

Therewere no significant differences among

ADHD subgroups in age

[F(2,

215) = .05,p = .96],

gender \yf(df = 2) = 2.0,p = .37], or ethnic group

composition[%2(4f

= 4) =

8.8,p =.07].

The

number

of children

in the

sample obtaining

the C, LA, and

HI diagnoses were

51

(1.9%),

123

(4.5%),

and 47

(1.7%),respectively.

Using a 0- to 3-point scoring system on the DSM

checklist,

the

followingscores were obtained

for the

total sample: LAsymptom total (M = 6.82, SD =

7.79),

HI

symptomtotal

(M = 4.22, SD =

6.29),

and

ODD symptom total (M= 2.94, SD = 5.35).

Behavioral Variables

One-wayanalysesofvariance (ANOVAs) were

executed

for

each

of the

nineteen dependent vari-

ables. Maineffects werefurtherevaluated using the

Tukey

(Tukey, 1972) test to explore group differ-

ences.Cell

sires,

means and standard deviations, F

andp values, andpost hoc comparisons for the be-

havior

ratings are reported in

Table

III.

On the

adjustment

variables, the three ADHD

groups were

all

rated

as

significantly more impaired

than the NC group on measures of Hard Working,

Appropriate Behavior, and Happy. Surprisingly, on

the fourth

adjustment

variable, Learning, the HI

group did not

differ

from

the NC

group, while

the

C and

LA

groups received significantly poorer ratings

than the NC and HI groups. Although more im-

paired than the NCgroup, the HI group received

higher ratings of Hard Working than the othertwo

ADHD groups, and higher ratings of Happy than the

Cgroup. However,theLAgroup obtained higherAp-

propriate Behavior ratings than the other two diag-

nosed groups.

On the three sociometric rating variables and

the TRF Social Problems scale, all three of the di-

agnosed

groups were rated

as

having poorer social

functioning than the NCgroup. The Cgroup re-

ceived higher ratingson the Peer Dislike than the

LAgroup and higher ratings on the TRF Social Prob-

lems variables than either the HI orLAgroups, which

did not

differ

significantly

from

each other oneither

variable. On the Peer Like variable, the

LA

group was

rated as liked by more peers than the C group, with

no significant

differences

betweeneitherof these two

groups

and the HI

group.

On the

Peer Ignore vari-

able,

there

were no differences among groups.


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ADHD Subtypes

1 7

Table

DDLGroup

Comparisons

on

Behavioral Ratings

a

Significant groupdifferences based

ADHD ADHD ADHD onTukey/wrthoctests

Variable C IA HI NC F-ratio

(p C

Disliked

by

2.96 2.27 2.65 1.50 35.62*

C, ffl and IA > NQ OIA

Peers (1.34) (1.29) (1.23) (0.86)

Peers

Neutral 112 2.22 1.98 1.44 18.5s C, HI. and IA>NC

Toward (1.21) (1.17) (1.18) (0.80)

ODD

symptom 16.09 7.13 15.02 3.65 71.0*

C and

HI>IA>NC

ratiag (6.64) (7.53) (6.74) (5.92)

Hardworking 1.67 1.68 3.26 4.32 116.9* NC>HI>C

and IA

(0.97) (0.98) (1.34) (1.64)

Appropriate 1.55 2.45 1.67 4.12 67.2* NC>IA>Cand HI

Behavior (0.87) (1.48) (1.15) (1.77)

Learning 1.84 1.82 3.67 4.17 86.4* NC andHI>C and IA

(1.03) (1.08) (1.49) (1.67)

Happy

2.53 3.08 3.42 4.32 30.8* NOC,

HI, and IA;

(1.26) (1.35) (1.69) (1.54) HI>C

Withdrawn

4.46 5.82 2.45 2.27 29.3* C andIA>HIand NC

(3.65) (4.52) (2.19) (2.86)

Somatic 1.78 1.12 0.67 0.53 7.2* C>HIand NC;IA>NC

Complaints (Z97) (2.13) (1.60) (1.24)

Anxious/

8.94 5.15 5.81 3.24 18.2* C>NIandIA>NC

Depressed

(6.35) (4.93) (5.75) (4.62)

Social 9.79 6.12 6.36 2.32

56.2*

C>HI andIA>NC

Problems

(5.02) (4.62) (4.45) (3.35)

Thought 1.80 1.16 1.79 0.35 15.9* C, HI, and IA>NC

Problems (2.54) (2.01) (Z47) (1.05)

Attention 29.89 25.8 18.98 8.03 218.4* C>IA>HI>NC

Problems (4.25) (6.16) (6.85) (7.90)

Delinquency 7.43 4.83 6.59 2.04 51.2* C andHI>IA>NC

(3.87) (3.63) (4.13) (2.87)

Aggressive 31.22 14.76 31,95 8.12 88.5*

C and

HI>IA>NC

Behavior (11.12) (12.82) (10.31)

(10.72)

Internalizing 14.35 11.57 8.36 5.85 21.2* C>HI

and NC;

IA>NC

Behavior (10.98) (8.84) (8.04) (7.06)

Externalizing

38.52 19.61 37.84 10.25 89.5* C and

Hl>IA>NC

Behavior (13.42) (15.47) (13.13) (13.07

Total

Problem 93.94 64.61 75.34 27.40 121.5*

C> HI and

IA>NC

Behavior (27.00) (26.93) (27.25) (26.54)

aADHD

=

attention

deficit

hyperactivitydisorder;

C =

combined type;

IA =

predominantlyinattentive;

HI =

hyperactive/impulsive;

NC =nondiagnosedcontrols. Mean

values

forADHDC,ADHD IA,

ADHD

HI, and NCgroupsare followed bystandard deviationsinparentheses.

bp


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1 8

Gaub andCarlson

Table IV.PercentageofChildreninADHD

Subtypes Classified

asImpaireda

Impairment

C IA HI

variable

(a =51) (n = 123) (n = 47)

Social(Peer Like

or

Dislike)

82 59 53

Behavioral

(Appropriate Behavior)

90 58 80

Academic(Learning) 82 76 23

NotImpairedin any of the

three

domains 2 11 4

aADHD = attention deficit hyperactivity disorder; C = combined type; IA =

predominantlyinattentive;HI =hyperactive/impulsive.

On all TRF externalizing variables (Aggressive

Behavior, Delinquency,

and

Externalizing Behavior)

and

the ODD symptom rating, the three diagnosed

groups received higher scores than

the NC

group.

No

differences

emerged between

the C and HI

groups,

with

both

receiving

significantly

higher ratings than

the IA

group

on all

variables. Thus,

on

externalizing

variables, the C and HI children are rated as most

deviant, while

the IA

children obtain lower ratings.

The

pattern

of

group differences

for the TRF in-

ternalizing variables

was

more complex than those

in

other domains.

On all

four internalizing variables

(Withdrawn, Somatic Complaints, Anxious/De-

pressed, and Internalizing Behavior), the C and IA

groups were rated

as

significantly more impaired than

the NC group. HI children received higher ratings

than NC children only on the Anxious/Depressed

variable; on all other internalizing variables, the HI

group

was

rated

as no

different than

the NC

group.

The C group was rated as having significantly more

problems than

the HI group on allfourvariables. The

IAchildren werenot significantly

different

from the

other two diagnostic groups on Somatic Complaints

or

Internalizing.

The IA

group

was

rated

as

more

Withdrawnthan the HI group, but the groups did not

differ on the other threeinternalizing variables.

On the Thought Problems scale,the three diag-

nosed groups were rated

as

significantlymore deviant

than the NC group, with the C group rated assignifi-

cantly more impaired than the HI and IA groups,

which

did not

differ from each other.

On the

Atten-

tion Problems scale, allthree diagnosed groups re-

ceived

significantly

higher ratings than

the NC

group,

with

the C

group receiving significantly higher ratings

than the IA group. The HI group received signifi-

cantlylower ratings than either the C or the IA group.

On the Total Problem scale the C groupwas

ratedby

teachers

as

having significantly higher scores

than anyother group. No differences emerged be-

tween the HI and IA groups, both of which were

rated as

having significantly

moreproblemsthan the

NC

group.

Impairment

Criteria

To

approximate

the

impairment criteria required

by

DSM-IV, NCscoreswere used to calculate objec-

tive

criteria

on various ratingitems.A child was con-

sidered impaired if he/she scored 1SD or greater

from the NC

mean

(in the

deviant direction)

in the

following domains: academic (TRF Learning), be-

havioral (TRF Appropriate Behavior), social (Peer

Dislike

or Peer Like). Table IV shows the proportion

of

children

in

each subtype

ratedas

unpaired

in

each

domain, and the proportion who did not meet im-

pairment criteria in anydomain.

As indicated, the C group was most pervasively

impaired, with percentages

of

children rated

as im-

paired

socially, behaviorally, and academically of

82%, 90%,

and

82%, respectively. Only

one C

child

(2%) did not show impairment in any domain.

AmongLAchildren, academic impairmentwasmost

common(76%), with moderate rates of social (59%)

and behavioral (58%) impairment.Few LAchildren

(11%) were rated as nonimpaired in anyarea.Chil-

dren in the HI group were most likely to show be-

havioral impairment (80%), with moderate rates

of

social impairment (53%)

and

relatively

lowratesof

academic (23%) impairment.Very few HI children

(4%) were rated as unimpaired in any domain.

DISCUSSION

Prevalence

The present findings in this nonreferred popu-

lation indicate that prevalence ratios varied

across

the

three ADHD subtypes, with

the

following rates;


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ADHD Subtypes

1.9 for C, 4.5%for LA, and 1.7% for HI. Thepro-

portionof the population identified as C(1.9%)was

slightly lower than prevalence estimates of ADHD

using

previous

diagnostic criteria, which are generally

cited

in the 2-3% range (APA,

1987).

While the cur-

rent

findingscouldmerely reflectthe stringent crite-

riaforsymptom presence (i.e.,a very muchraring),

it ispossible

that changes

in

diagnostic criteria have

decreased

the prevalence of the C subtype. If, as sug-

gestedby the field

trials (Lahey

et

al., 1994), most

children meeting criteria

for the HI

subtype would

likely have been diagnosed byclinicians ashaving

ADHD(according

to

DSM-III

and

DSM-C

III-R

cri-

teria),the current results showing a 3.6% prevalence

of

these

two

subtypes combined (1.9%

for C and

1.7

for HI) appear consistent with previous preva-

lence

estimates.

The

rate

of IA was also higher than previous

ADD/WO

prevalence rates

of approximately 3%

(Szatmari

et al.,

1989).

This was

likely

due to the

change in diagnostic criteria resulting in more chil-

dren

qualifyingfor an LAdiagnosis; this conclusion

isconsistent with the DSM-IV field trials (Lahey et

al., 1994) findingthatthe majorityof the new cases

identified by DSM-IV were IA children.

Thehigher rates

of all three subtypesfound in

previous

population-based studies of DSM-IV crite-

ria

(Baumgaertel

et al., 1995; Wolraich et al., in

press)werelikely

due to the more lenient

cutoff

cri-

teria employed in those studies, bothof which em-

ployed

slightly

differently

phrasingforanchor points,

butcounted symptoms

as

present

if

either

of the two

mostextremeratings (i.e.,often or very

much)

were

endorsed.

Despite

some differences in relative pro-

portions of the subtypes, both previous studies and

thecurrent studyfound that

LA

wasmost prevalent,

and

HIleast prevalent, in nonreferred populations.

An interesting

difference between current re-

sults

and

those from

research using clinic-referred

samples(Laheyetal., 1994;

McBurnett

et al., 1995)

involvesthe relative

ratios

of the

three

ADHD sub-

types. In the

current study,

LA was

identified twice

as

often as C(C:IA ratio of1:2.4);conversely, both

the field trials (Lahey et al., 1994) andMcBurnett

et al.(1995) found C to be much more prevalent

than

LA

(C:IA ratios of 2.1:1 and3.5:1,respectively).

In addition, while the current study found nearly

identical ratesof

C

and

HI C: Hl

ratio

=

1.1:1),

both

previous studies (Laheyetal., 1994; McBurnett

et al., 1995) found much higher CM ratios (3.0:1

and4.3:1,respectively).Thesediscrepancies

in

preva-

1 9

lence

ratios likely reflected

the

nature

of the

samples

(population-based

vs.

clinic-referred).

Relatedly,

Wolraichet al. (in press) found that C children were

two

to four times more likely than

LA

or HI children

to be

referred

to a

clinic.

Behavioral

Characteristics

The distinctive pattern of impairment by subtype

found in the current study clearly indicates that the

DSM-IV diagnostic system distinguishes three groups

of

children that are all impaired, relative to nondi-

agnosed controls, and that can be differentiated from

each other based on differentpatternsof difficulties.

The C

subtype

was

associated with

the

most perva-

sive

pattern ofdifficulties,with severe ratingsof im-

pairment found

in all

major domains

of

functioning.

For variables includingAnxious/Depressed, Social

Problems, Attention Problems,

and

Total Problem

Behavior, the C group was rated as more unpaired

than

any of the

other groups.

As

noted earlier, this

pattern

of

pervasive deficits displayed

by C

children

is consistent with that shown in children diagnosed

using previous ADHD

criteria.

In the DSM-IVfield

trials sample, Lahey

et al.

(1994)also demonstrated

that C children experienced extensivedifficulties,and

were significantly impaired

in all

assessed areas

in-

cluding social, academic, and global functioning.

The IA

children, like

the C

children, were rated

by

teachers

as significantly

impaired

in all

major

do-

mains

of functioning. Nonetheless, the LAchildren

demonstrated areas of advantage relative to the other

two diagnosed groups. Specifically,

the LA

children

were perceived as displaying more appropriate behav-

ior and

less externalizing behavior than

C or HI

chil-

dren.

Previous research comparing ADD/WO and

ADD/H children found that ADD/WO children

showed

more internalizing behavior, but less external-

izing

and

antisocial behavior,

and

lower

ratesof

peer

rejection, than those

with

ADD/H (Lahey

et

al.,

in

press).This pattern

is

consistent with

the

present

find-

ings, with IA children receiving significantly lower

TRF ratings on Aggression, Delinquency and Exter-

nalizingscales, lower

ODD

symptomscores,lower

Peer Dislike ratings, and higher Peer Like ratings than

C children. Surprisingly, however, LA and C children

were rated as no different fromeach other (although

both received

significantly

higher

scores

than NC chil-

dren) on three internalizing variables (Withdrawn, So-

matic Complaints

and Internalizing Behavior).


8/9

11

Furthermore, although they did differ on theAnx-

ious/Depressed rating, this difference

was in the un-

expected direction; the C children were rated as more

Anxious/Depressed than

the IA

children. This

finding

parallels those of Wolraich et al. (in

press),

who also

found cooccurring anxiety/depression to be more

common

among

C

(29.3%) than

IA

(21.9%)children.

While

this unexpected result may be attributable

to the

revised diagnostic criteria,

it

seems unlikely

that the changes would produce such a strong effect

A closer examination of past research, as reviewed

byLahey, Carlson,

and

Frick

(in

press),suggests that

the epidemiological (school-based) studies available

(Lahey,

Schaughency, Strauss, & Frame, 1984; Pel-

ham,

Atkins, Murphy,

&

White, 1981)

did not find

differences in

anxiety/depression between

the

ADD/H

and

ADD/WO subgroups. Rather, these dif-

ferences were evident primarily in studies using

clinic-referred samples

(e.g.,

Lahey, Schaughency,

Hynd,

Carlson, & Nieves,1987).There may be a re-

ferralbias operating such that those

IA

children

with

highlevelsofanxietyanddepressionaremore likely

to be referred to clinics. Thus, IA (or ADD/WO)

childrenwho are includedin clinic-referred popula-

tions may be more anxious/depressed than their

counterparts in the overall population, resultingin

this

discrepancy across studies.

The HI

group

in the

current study demonstrated

a

pattern

of

impairment that

was

quitedifferent than

that of the C and IA groups. While the HI group

received significantlypoorer ratings than the NC

group in the

socialfunctioning,externalizing, atten-

tion, andthought problems domains, theydid notdif-

fe r significantly from

NC

children

on

several

variables, including

the

Learning

and

most internal-

izingsubscales (Withdrawn, Somatic Complaints,

and

Internalizing).

In

addition,

the HI

group

was

rated

assignificantlymore hard working than

the IA and

C

groups

and

significantlyhappier than

the C

group.

Thus, consistent with existing research (Baumgaertel

et

al., 1995; Laheyetal., 1994; McBurnettet al,1995;

Wolraich et al., inpress),HI children appear to be

characterized byexternalizingand peer relationship

problems, but do not demonstrate internalizing prob-

lems

or academic impairment. Overall, the results

from this

and

other research indicate that

the new

subtypeof HI is a valid and useful addition to the

DSMdiagnostic system; HI children are significantly

impaired

in some areas of functioning, but the pat-

tern of behavioral problems is distinctly different

from that

found

among

IA and C

children.

Gaub andCarlson

The younger age of onset for HI reported in the

field trials (5.65 years) (Lahey et al., 1994) led to

speculation that, rather than representing

a

separate

ADHD subtype, younger, Hi-diagnosed children

might

eventually display inattentive symptoms

and

qualify

for C diagnoses (Barkley,

1997).

In the

McBurnettet al.(1995)sample, the HI subtype was

also significantly younger than the C or IA subtypes;

however, the mean HI age (7.25 years) was not as

young

as

that reported

in the field

trials. Further-

more,

in the

current study,

no

significant

age differ-

enceswere

found

among the C(M= 7.6 years), IA

(M = 7.6

years),

or HI

(M =

7.5

years) groups. Since

disruptive,hyperactive behavior would likely lead to

referral

at an

earlier

age than inattentive, less dis-

ruptive

behavior, the younger ages for HI children

in

studies using clinic samples (Lahey et. al, 1994;

McBurnett

et al., 1995) mayreflect referral patterns

rather than true differences across subtypes in age

of onset.Thus,

the

current

findings of

different

as-

sociated impairment

for the HI

subtype, along with

evidence that this subtype

was

found

in all age

groups, support the validity of HI as a distinct sub-

type of ADHD rather than a precursor to C.

Limitations

There

are

several limitations

of the

current study.

The

exclusive

use of

teacher ratings

on a

symptom

checklist

to

assign diagnoses

is

problematic, since nei-

ther the age of onset of symptomsnor information

regarding impairment

or

cross-situationality

was ob-

tained.In an attempt to address this limitation within

the parameters of the available data, the strictest pos-

siblecut-off scores were implementedfor theSNAP-

IV The low

proportion

of

children

(2% of C, 11% of

IA, and 4% of HI) who

were

not

rated

as

unpaired

in

any

realm suggests that

the

current study appro-

priately avoided identifying subthreshold cases. The

study

is

also limited

by its

reliance

on

teachers

for

both diagnostic and dependent variable ratings, al-

though the finding of

different

patterns ofbehavior

problems across subtypes provided evidence

of the as-

sociation

between teacher perceptions of diagnostic

symptoms

anddomain-specific

dysfunction

.

Another

limitation

of the present study is the

extent

to

which theseresults

are

generalizable

to the

overall population since the current sample consisted

primarily

of lower-SES Hispanicsubjects. However,

the consistency of the obtained pattern of results


9/9

ADHD

Subtypes

111

(particularlyregarding group differences

in

areas

of

functioning) with findings

from

previous

research

suggests that ADHD children

from

both minority

andnonminorityethnic backgrounds share common

behavioral

characteristics.

Thisand other research supports the concurrent

validity of the DSM-IV ADHD subtypes. The com-

parability of the current results and those of the

other two population-based studies (Baumgaertel et

al., 1995; Wolraich et ah, in press), which used pri-

marily

Hispanic,German, and Caucasian subjects, re-

spectively, establishes the cross-cultural congruency

of

behaviors associated withADHD. Future research

should work toward examining the etiological and

predictivevalidity of the current diagnostic system by

exploring potential subtype differences in causes,

outcomes,

and

treatment responsiveness.

ACKNOWLEDGMENTS

Thisstudywas made possible through collabora-

tion

with

the

Hogg Foundation School

of the

Future

Project (SOF).The authors thank Wayne Holtzman,

Ph.D.,

Special Consultant to the Hogg Foundation,

as well as Scott Keir,

Ph.D.,

SOF

Director

of Re-

search,

and Pam

Diamond, Ph.D.,

SOF

Senior

Re-

searchAssociate,

for their enthusiastic support. Also,

thanks

to

Anne Anderson, Joey Martin,

and

Scott

Davis

fortheir

manyhours

of

data entry.

This

research

was partially supported by an

NIMHFIRST grant, MH49827 awardedto the sec-

ond

author.

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