Trends in the Prevalence of Developmental Disabilities in US Children, 1997-2008 (Boyle, 2011)

Trends in the Prevalence of Developmental Disabilities in USChildren, 1997–2008

WHAT’SKNOWNONTHISSUBJECT: USdata on the changes in the prevalence of developmental disabilities are scarce. Although there are a fewstudies on individual disabilities, data examining the impact of the full range of developmental disabilities are unavailable.

WHAT THISSTUDYADDS: Developmental disabilitiesmake a significant contribution to overall childhoodhealth.We show the health disparities that exist for specific populations andhow selected conditions have increasedover the past 10 years.

abstract OBJECTIVE: To fill gaps in crucial data needed for health and educa- tional planning, we determined the prevalence of developmental dis- abilities inUSchildrenand inselectedpopulations forarecent12-year period.

PARTICIPANTSANDMETHODS:Weuseddata onchildrenaged3 to 17 yearsfromthe1997–2008NationalHealth InterviewSurveys,whichare ongoing nationally representative samples of US households. Parent- reported diagnoses of the following were included: attention deficit hyperactivity disorder; intellectual disability; cerebral palsy; autism; seizures; stuttering or stammering; moderate to profound hearing loss; blindness; learning disorders; and/or other developmental delays.

RESULTS: Boys had a higher prevalence overall and for a number of select disabilities comparedwith girls. Hispanic childrenhad the low- est prevalence for a number of disabilities compared with non- Hispanicwhiteandblackchildren.Lowincomeandpublichealth insur- ance were associated with a higher prevalence of many disabilities. Prevalence of any developmental disability increased from 12.84% to 15.04%over 12 years. Autism, attention deficit hyperactivity disorder, and other developmental delays increased, whereas hearing loss showed a significant decline. These trends were found in all of the sociodemographicsubgroups,except forautisminnon-Hispanicblack children.

CONCLUSIONS: Developmental disabilities are common andwere re- ported in �1 in 6 children in the United States in 2006–2008. The number of childrenwith select developmental disabilities (autism, at- tentiondeficithyperactivitydisorder,andotherdevelopmentaldelays) has increased, requiringmore health and education services. Additional study of the influence of risk-factor shifts, changes in acceptance, and benefitsofearlyservices isneeded.Pediatrics2011;127:1034–1042

AUTHORS: ColeenA. Boyle, PhD,a ShereeBoulet, PhD,a

LauraA. Schieve, PhD,a RobinA. Cohen, PhD,b StephenJ. Blumberg, PhD,bMarshalyn Yeargin-Allsopp,MD,a

SusannaVisser,MS,a andMichaelD. Kogan, PhDc

aNational Center onBirthDefects andDevelopmental Disabilities and bNational Center for Health Statistics, Centers for Disease Control andPrevention, Atlanta, Georgia; and cMaternal and Child Health Bureau, Health Resources andServices Administration, Rockville,Maryland

KEYWORDS developmental disabilities, prevalence, autism, attention deficit hyperactivity disorder

ABBREVIATIONS NHIS—National Health InterviewSurvey ADHD—attention deficit hyperactivity disorder

All authorsmadesubstantial intellectual contributions to thestudy, including theconceptionanddesign,acquisitionofdata,analysis, and interpretation.All authorsparticipatedactively in thedrafting andrevisingof themanuscript. Finally, all authorsapproved the final version thatwassubmitted forpublication.DrColeenA.Boyle had full access toall thedataandtakesresponsibility for the integrityof thedataandaccuracyof thedataanalysisand contributed to thestudydesignandconcept, analysisand interpretationof thedata,draftingof themanuscript, critical reviewof themanuscript, andstatisticalanalysis.DrShereeBoulet contributed to thestudydesignandconcept, acquisitionof thedata, analysisand interpretationof thedata,andcritical reviewof the manuscript.DrLauraSchievecontributed to thestudydesignand concept, analysisand interpretationof thedata,draftingof the manuscript, andcritical reviewof themanuscript.DrRobinA. Cohencontributed to theacquisitionof thedataandanalysisand interpretationof thedata.DrStephenJ.Blumbergcontributed to theanalysisand interpretationof thedata,draftingof the manuscript, andcritical reviewof themanuscript.DrMarshalyn Yeargin-Allsoppcontributed to theanalysisand interpretationof thedata,draftingof themanuscript, andcritical reviewof the manuscript.DrSusannaVissercontributed to theanalysisand interpretationof thedata,draftingof themanuscript, andcritical reviewof themanuscript.DrMichaelD.Kogancontributed to the analysisand interpretationof thedata,draftingof themanuscript, andcritical reviewof themanuscript.

The findings and conclusions in this report are those of the authors anddonot necessarily represent the official position of the Centers for DiseaseControl andPrevention or theHealth Resources andServices Administration.

www.pediatrics.org/cgi/doi/10.1542/peds.2010-2989

doi:10.1542/peds.2010-2989

Accepted for publication Feb 25, 2011

Address correspondence to Coleen A. Boyle, PhD, National Center onBirthDefects andDevelopmental Disabilities, Centers for DiseaseControl andPrevention, 1600CliftonRd, Atlanta, GA 30333. E-mail: [email protected]

(Continuedon last page)

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Dataontheprevalenceofdevelopmen- tal disabilities have been used to de- scribe the importance of these health problems and to assess the educa- tional, medical, and social support needs forchildrenwithdevelopmental disabilities and their families. Esti- mates of the prevalence of develop- mental disabilities in US children on the basis of the 1988 National Health Interview Survey (NHIS) indicated that 16.8% of children younger than 18 years of age had lifelong conditions arising inearlychildhoodasaresultof cognitive or physical impairment or a combination of the 2.1 Findings from morerecent surveys thatusedamore restrictive definition of developmental disabilities suggested that 13.2% of childrenhad1ormoredevelopmental disabilities during 1997–2005 and 1.6% had 3 or more developmental disabili- ties.2Thesestudiesalsodocumentedthe considerable impactof thedisordersas measuredbyhigher ratesof healthand special-education service use for chil- dren with developmental disabilities compared with children without devel- opmentaldisabilities.

Anumberoffactorsmayhaveinfluenced theprevalenceofdevelopmentaldisabil- itiesover thepast10 to15years, includ- ing improved survival of the growing number of children born preterm or with birth defects or genetic disorders, such as spina bifida and Down syn- drome,3 whose improved survival may beoffsetbyadisproportionateburdenof neurologic and other impairments.4,5

Other trends and medical practice changes that might contribute to a re- duction of developmental disabilities in thepopulation include increases inpre- natal diagnosis and therapeutic abor- tion,oldermaternalage,newinfantvac- cines, and the expansion of newborn screening.6,7 Finally, increased aware- nessand improveddiagnosis, particu- larly for conditions with a behavioral phenotype,suchasautismorattention

deficit hyperactivity disorder (ADHD), mayhave contributed to changesover time.

Since 1997, the NHIS has routinely in- cluded questions on a broad array of developmentaldisabilitiesamongchil- drenyoungerthan18yearsofage.This survey, with population-based annual samplesandconsistent verbiage in in- dividual disability conditionquestions, is ideal formonitoring trends in prev- alence over time. We used data for a 12-year timeperiod (1997–2008) toex- amine (1) the national prevalence of developmental disabilities according to major demographic and socioeco- nomiccharacteristicsand(2)changes in the prevalence of developmental disabilities over time.

PARTICIPANTSANDMETHODS

We used the Family Core and Sample Child Components of the NHIS from 1997 to 2008. The NHIS is an ongoing annual survey, conducted by the Cen- ters for Disease Control and Preven- tion, National Center for Health Statis- tics, thatusesamultistageprobability sample toestimate theprevalenceofa number of health conditions in the ci- vilian noninstitutionalized population of the United States.8,9 Demographic and health data on family members

are obtained through an in-person in- terview with a knowledgeable adult family member. For the Sample Child component,moredetaileddataareob- tained for 1 randomly selected child youngerthan18yearsofage.Formore than 90% of the children included in theNHIS Sample Child component, the knowledgeable adult interviewed was aparent or legal guardian.

The current analysis was limited to children aged 3 to 17 years (total 1997–2008 unweighted sample size: 119367). Children younger than 3 years of age were excluded because many developmental disabilities are not recognized or diagnosed before that age. The average household re- sponse rate for the NHIS was 88.3% (range of annual rates: 84.9–91.8%); the average conditional response rate for the sample child component was 91.2% (range: 85.6–93.7%).

The specific conditions assessed were asfollows:ADHD;cerebralpalsy;autism; seizures; stammering or stuttering; mental retardation; moderate to pro- found hearing loss; blindness; learning disorders; and other developmental de- lays (see Table 1 for the survey ques- tions). Thesamesetofquestionswere askedover the11survey years; theex-

TABLE1 TheNHIS Questions onDevelopmental Disabilities, 1997–2008

Condition Survey Question

ADHD/attention deficit disorder (ADD),a

autism, cerebral palsy,mental retardation,b andother developmental delay

“Has adoctor or health professional ever told you that [survey child] hadany of the following conditions?”

Seizures and stuttering or stammering “During the past 12months, has [survey child] had any of the following conditions?”

Moderate to profoundhearing loss “Which statement best describes [survey child’s] hearingwithout a hearing aid: good, a little trouble, a lot of trouble, or deaf?”c

Blindness “Is [survey child] blind or unable to see at all?” Learningdisability “Has a representative from the school of a health

professional ever told you that [survey child] has a learningdisability?”

aNHIS shifted fromasking about ADD in 1997–1999 to asking about ADDandADHD in 2000 and later. bReferred to as intellectual disability in the text and tables. cCategorieswere revised in 2008 to the following: excellent; good; a little trouble;moderate trouble; a lot of trouble; and deaf. Moderate to profound hearing loss included the categories of deaf and a lot of trouble hearing for 1997–2007 and moderate trouble, a lot of trouble, anddeaf for 2008.

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ception was an expansion of the hearing-loss categories in 2008 (see Table 1 for details). Although the NHIS questionnaire used the term “mental retardation,” to be more closely aligned to currently accepted termi- nology, we refer to this condition as “intellectual disability.”10 The time framefor themajorityof thequestions refers towhether the childwas “ever” diagnosed with the condition; for sei- zures and stuttering or stammering the reference periodwas the “past 12 months,” and moderate to profound hearing lossandblindnessreferred to the current status of the child. A child was considered to currently have a condition if there was an affirmative response, regardless of the time frameof thequestions.Therewassub- stantial collinearity between learning disabilities and intellectual disabili- ties, andwe therefore report learning disabilitiesasaconsequenceof the in- tellectual disability rather than a co- occurring condition. That is, children with reported intellectual disabili- ties and learning disabilities were only included in the intellectual dis- ability category.

We examined the prevalence of any parent-reported developmental dis- abilities and of each individual devel- opmental disability for the 12-year pe- riod combined and assessed how the estimatesvariedbyanumberofdemo- graphicandsocioeconomiccharacter- istics, includingthechild’sage;gender and race/ethnicity; mother’s educa- tion; total family income level from all sources, includingsupplemental secu- rity income (with incomedefined rela- tive to the federal poverty level); and health insurance status (any public, private-only, no health insurance re- ported). Children covered by both pri- vate insurance and the state’s Medic- aidprogramsare includedunder “any public.” We also assessed secular trends foreachdisabilityover43-year

time intervals (1997–1999; 2000–2002; 2003–2005; and 2006–2008). For the disabilities with statistically signifi- cant temporal trends, we conducted additional analyses to determine whether trends were uniform within the demographic and socioeconomic subgroups. Income stratification in this report is based on both reported and imputed income.11

Prevalence estimates were weighted usingNHISweightstorepresent theUS noninstitutionalizedpopulationof chil- dren. Variance estimates were pro- duced using Sudaan software to ac- count for the complex NHIS sample design. �2 Tests were used to deter- mine whether the prevalence esti- mates differed among the various groups being compared. Wald-F tests wereusedtoassess lineartrendsover the 4-calendar-year time periods. All associations and differences de- scribed in the text were statistically significant at theP � .05 level. Human subject review was not required for this analysis of publicly availabledata.

RESULTS

Prevalence andDemographic Characteristics

The prevalence of any developmental disability in 1997–2008 was 13.87% and ranged from 0.13% for blindness to6.69%forADHDand7.66%for learn- ing disabilities (Table 2). In general, there was higher prevalence in older childrenforconditions likely tobefirst recognized or confirmed in the school years, including ADHD and learning disabilities. Little change across age groups was noted for cerebral palsy, moderate to profound hearing loss, andotherdevelopmentaldelays.There was a lower prevalence in older chil- dren for stuttering or stammering. Hispanic children had a lower preva- lence of several disorders relative to non-Hispanic white and black chil- dren, including ADHD and learning

disabilities; the prevalence of other developmental delays was higher only in comparison to non-Hispanic whitechildren.Stutteringorstammer- ing was reported more often in non- Hispanic black children than non- Hispanicwhite children. Boys had twice theprevalenceofanydevelopmentaldis- ability and excess prevalence for ADHD, autism, learning disabilities, stuttering or stammering, and other developmen- taldelays, specifically.

There was a nearly twofold higher prevalence of any reported develop- mental disability among children in- suredbyMedicaid relative to those in- sured by private insurance, and this patternwasstatisticallysignificant for ADHD, learning disabilities, intellec- tual disabilities, seizures, stuttering or stammering, and other develop- mental delays. Family incomes below the federal poverty level were associ- ated with a higher prevalence of parent-reported developmental dis- abilities overall and learning disabili- ties, intellectualdisabilities, stuttering or stammering, and other develop- mental delays, specifically. Lowerma- ternal education (ie, any attainment less than a college degree)was associ- atedwithahigherprevalenceofanyde- velopmental disabilities, learning dis- abilities, andstutteringorstammering.

Time Trends

Forall developmentaldisabilitiescom- bined, there was a small, but statisti- cally significant, linear increase in the prevalence over the 4 time periods, from12.84%in1997–1999 to15.04%in 2006–2008 (Table 3). Of the individual disorders, ADHD and autism showed significant and successive increases overtime.Otherdevelopmentaldelays, a catch-all category, also showed sig- nificant increases over the time pe- riod, but the increase was observed only between themost recent 2 inter- vals (from 2003–2005 to 2006–2008).

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ADHD, because of its considerably higherprevalence,waschieflyrespon- sible for theupward trend in theover- all prevalence of developmental dis- abilities, with a 33% increase in prevalence from 1997–1999 to 2006– 2008. Autism, however, showed, by far, the largestrelative increase,withnearly a fourfold change froma prevalence of 0.19% in 1997–1999 to 0.74% in 2006– 2008.Moderatetoprofoundhearingloss was theonlydisorder todecline inprev- alence, showing a 31% decrease from 1997–1999 to2006–2008.

Although themagnitude of the change varied somewhat among the various descriptive factors (Table 4), in gen- eral, we observed upward trends in the parent-reported prevalence of ADHD and autism and a decrease for moderate to profound hearing loss. One exception was race/ethnicity and autism, with a lack of a significant in- crease in non-Hispanic black children.

DISCUSSION

Developmentaldisabilitiesaffectasig- nificant proportion of children in the United States. We found that 15% of children aged 3 to 17 years, or nearly 10millionchildrenin2006–2008,hada developmental disability on the basis of parent report. The 17% increase in prevalence over the 12-year period represents�1.8millionmorechildren with developmental disabilities in 2006–2008 thanadecade earlier.

It is difficult to corroborate theoverall prevalence reported in this study be- cause of the lack of comparable stud- ies using a similar grouping of condi- tions. In comparing theprevalence for individual disorders, however, we find good agreement for someof the prev- alence estimates. A comparable high prevalence of ADHD recently was re- ported from the 2003–2007 National Survey of Children’s Health, using a similar set of parent-reported survey questions.12 Prevalence rates for au- TA B LE 2 Pr ev al en ce of D ev el op m en ta lD is ab ili ti es in Ch ild re n Ag ed 3 to 17 Ye ar s, by Se le ct ed D em og ra ph ic an d So ci oe co no m ic Fa ct or s, N H IS ,1 99 7– 20 08

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tism,cerebralpalsy,seizures,blindness, and stuttering or stammering are com- parable with those from several population-basedprevalencestudiesus- ing varied study methods.13–18 This is particularly relevant for seizures, where the nomenclature, as en- dorsed by the International League Against Epilepsy, for recurrent sei- zures is epilepsy and not seizures or seizure disorder.18 The prevalence of moderate to profound hearing loss was considerably higher, whereas theprevalenceof intellectualdisabil- ities was �50% lower than findings from a population-based surveil- lance program that requires audi- tory test results formoderate topro- foundhearing lossandcognitive test results for intellectual disabilities.17

A number of factors may have influ- enced these discordant findings, in- cluding amore restrictive case defi- nition in the records-based surveillance program for moderate to profound hearing loss (ie, bilat- eral measured loss of 40 dB or greater) than that used in the NHIS analysis. In the case of intellectual disabilities, and particularly mild in- tellectual disabilities, because test- ing often is done in the context of educationalplacement, theparentor

guardian may never have been told that their child’s test results sug- gested functioning in the intellectual disabilitiesrange.Also,since1997, fed- eral lawhasallowedforstateandlocal education agencies to extend the use of the less-specific “developmental de- lay” category up to 9 years of age, en- abling many children to not require a more specific education classifica- tion, such as intellectual disability.19

Someof thesechildrenmayhavebeen identified in the NHIS by the question “other developmental delay,” as sug- gested by the high and increasing prevalence for this category.20 Al- though it is not clear what specific functional problems children with otherdevelopmental delayshave, Bou- let et al2 showed that 76% have a co- occurring developmental disability andthat learningdisabilitiesandADHD were the most frequent co-occurring conditions.

The 17% increase in all developmental disabilities over the 12 years was caused in large part by shifts in the prevalence of ADHD and autism. In- creases in autism during the mid- 1990s to late 1990s and continuing through the late 2000s have been noted in a number of studies14,19,21–23

usingvaryingdefinitionsofautismand study designs, ranging from adminis- trativeeducationalandservicesystem data to retrospective studies of suc- cessive birth cohorts of children. Al- thoughdataontrendsinADHDareless available, they support a similar in- crease.23,24 A Danish study23 reported that trends in the birth cohort prev- alence of several neuropsychiatric disorders, including autism and hy- perkinetic disorder (International Classification of Diseases 10 Revi- sion classification that is closely aligned with the hyperactivity com- ponent of ADHD) increased signifi- cantly for children born in 1990 through 1999. A US-based study24 re- ported significant increases in the prevalence of office-based visits for ADHD during 1991–1998. Finally, an upward trend in prevalence, using US education data, was found for the “otherhealth impaired”educationcat- egory,which, since 1991, is the educa- tion category used for children with ADHD.19,25 Decreases in the prevalence ofmoderate to profound hearing loss over the 12-year period have not been reported previously. Trend data from service records over a shorter time frameshowed little tonochange.17Na- tionally, the number of infants identi-

TABLE3 Trends in Prevalence of SpecificDevelopmental Disabilities in Children Aged 3 to 17 Years, NHIS, 1997–2008

Disability n (Unweighted)

All Years,% 1997–1999,% 2000–2002,% 2003–2005,% 2006–2008,% Percent Change 1997–1999 versus 2006–2008c

Any developmental disability 15956 13.87 12.84 13.70 13.88 15.04 17.1d

ADHD 7652 6.69 5.69 6.71 6.77 7.57 33.0d

Autism 537 0.47 0.19 0.35 0.59 0.74 289.5d

Blind/unable to see at all 160 0.13 0.11 0.15 0.12 0.13 18.2 Cerebral palsy 305 0.39 0.39 0.43 b b b

Moderate to profoundhearing loss 533 0.45 0.55 0.44 0.42 0.38 30.9 Learningdisability 8154 7.04 6.86 7.24 6.82 7.24 5.5 Intellectual disabilitya 868 0.71 0.68 0.73 0.75 0.67 �1.5 Seizures, past 12months 792 0.67 0.66 0.65 0.66 0.72 9.1 Stuttered or stammered, past 12months 1924 1.60 1.63 1.40 1.69 1.68 3.1 Other developmental delay 3978 3.65 3.40 3.28 3.67 4.24 24.7d

Source: Centers for DiseaseControl andPrevention, National Center for Health Statistics, NHIS. aSurvey question askedaboutmental retardation, butwe refer to the condition as intellectual disability. bWe excluded cerebral palsy from the analysis for 2004–2007because of the high likelihoodof interviewer error arising fromaquestionnaire change in 2004. cPercent changebetween 1997–1999 and2006–2008. d Test of linear trendover 4 timeperiods,P � .05.

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fied with congenital moderate to pro- found hearing loss from state newborn-screening programs has in- creased dramatically with the expan- sionofuniversalscreening26;however, it is unlikely that this program would have impacted the prevalence for this survey. The lower prevalence of mod- erate to profound hearing loss from the NHIS was limited to 2006–2008; in 2008, therewas amodification in the moderate to profound hearing loss categories, which makes it difficult to determine whether this lower trend continues. More data are needed to better understand this finding.

Factors responsible for increases in autismandADHDarenumerous. Avail- ability of services and in how the ser- vicesystemclassifieschildrenwithbe- havioral disorders has progressed as welearnmoreabouttheadvantagesof earlier interventions. Improvements in clinical,parental,andsocietalrecogni- tion of and screening for these disor- ders have occurred. For example, we have national campaigns to increase awareness of autism,27 and the American Academy of Pediatrics has incorporated ongoing monitoring of a child’s development as a practice recommendation forpediatricians in 2007.28 Another contributing factor maybetheefficacyofmedicationsand behavioral treatments for ADHD.29

Therealsohasbeenan increase in the prevalenceofknownprenatal risk fac- tors for these conditions. Examples in- clude increases in the prevalence of preterm birth and the recognition of the full range of potential adverse developmental consequences of late preterm birth,4,5 shifts toward older parental age, and increases in the prevalence of assisted reproductive technologies and possibly other hor- monal infertility treatments and the consequent increase in multiple births, each of which is associated TA B LE 4 Pr ev al en ce of AD H D ,A ut is m ,a nd M od er at e to Pr of ou nd H ea ri ng Lo ss in Ch ild re n Ag es 3 to 17 ye ar s, by Se le ct Ch ar ac te ri st ic s an d Ti m e Pe ri od ,N H IS ,1 99 7– 20 08

Ch ar ac te ri st ic s

AD H D ,%

Pe rc en ta ge

Ch an ge

19 97 – 19 99

ve rs us

20 06 – 20 08

Au ti sm ,%

Pe rc en ta ge

ch an ge

19 97 – 19 99

ve rs us

20 06 – 20 08

M od er at e to Pr of ou nd H ea ri ng Lo ss ,%

Pe rc en ta ge

Ch an ge

19 97 – 19 99

ve rs us

20 06 – 20 08

19 97 – 19 99 20 00 – 20 02 20 03 – 20 05 20 06 – 20 08

19 97 – 19 99 20 00 – 20 02 20 03 – 20 05 20 06 – 20 08

19 97 – 19 99 20 00 – 20 02 20 03 – 20 05 20 06 – 20 08

Ag e, y 3– 10

4. 16

4. 80

4. 74

5. 19

24 .8

0. 27

0. 40

0. 72

0. 87

22 2. 2

0. 54

0. 43

0. 45

0. 34

� 37 .0 4

11 – 17

7. 51

8. 90

8. 98

10 .2 4

36 .4

0. 11

0. 31

0. 45

0. 59

43 6. 4

0. 57

0. 46

0. 37

0. 43

� 24 .5 6

G en de r

M al e

8. 43

9. 55

9. 44

10 .5 9

25 .6

0. 31

0. 58

0. 94

1. 12

26 1. 3

0. 65

0. 57

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ARTICLES

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with adverse developmental out- comes.30 Finally, given that the shift in developmental disability prevalence over timeseems tobe focusedoncon- ditions thatarebasedonanemotional or behavioral phenotype, a societal shift in the acceptance and destigma- tization of such conditions in young children alsomayplay a role.31

Several of our findings regarding the descriptive characteristicsof children with developmental disabilities were noteworthy. Others studies have re- ported lowerprevalenceestimates for autism and ADHD in Hispanics,12,14,32,33

although findings from more recent studies suggest that the gapsmay be closing.13 Rather than these patterns reflecting true differences, they are more likely the result of languagebar- riers, lack of access to services, and health insurance coverage. The pre- dominanceofboyswithdevelopmental disabilities also was remarkable. Al- though the increased gender ratio for selected developmental disabilities is well described, this study showed the pattern present for nearly all develop- mental disabilities. Some of this is cer- tainlybiological,suchasX-linkedgenetic disorders that result in intellectual dis- abilitiesandotherfunctional limitations. Others have described a cultural fac- tor related to greater incentive for case finding in boys compared with girls.34 Alternatively, there may be gender-specific presentations of some of the disorders, particularly for condi- tionswithanexclusivelybehaviorpheno- type (ADHD and autism) that favor the identificationofboysovergirls.ADHDisa goodexample,inthatgirlstendtoexhibit less of the impulsivity associated with the disorder and therefore maybe be less likely tocometoclinicalattention.35

Regarding socioeconomic inequities, public health insurance coverage

seemed tobeassociatedwithahigher prevalence of developmental disabili- ties; lowfamilyincomeandlowmaternal education had similar but less signifi- cant impacts. Larson and Halfon36

showedasimilarinversesocioeconomic gradient with family income and the prevalenceofADHD,learningdisabilities, and speech problems but not autism. Some of the impact with public insur- ance is likely reflecting eligibility for Medicaid forchildrenwithdisabilities.

The strengths of the NHIS are impor- tant to highlight. The survey has a na- tionally representative sample that al- lows for generalizability to the US population of 3- to 17-year-old chil- dren. The same set of questions was asked of parents in each survey year. Asaconsequence, this istheonlystudy able to examine, in detail, trends in these disorders. The response rate for the NHIS remained at exemplary high levels over the 11 years, despite the challenges of door-to-door sur- veys, limitingourconcernsabout the bias resulting from selectivity and nonresponse.

Limitations also are important to con- sider. Parent report ofmedical condi- tions is not without error. Inaccurate reportingcanresult fromparentaldis- tress and the stigma associated with some of the conditions; the questions may be misunderstood or there may bevariations inprofessional terminol- ogy used for developmental disabili- ties; for example, autism can be re- ferred to by more broad or umbrella terms,suchasautismspectrumdisor- ders. Also, specific terms fall outofac- cepteduse(mental retardationversus intellectual disability and seizure dis- order versus epilepsy). A few stud- ies33,37,38 have examined the validity of parent report for selected develop- mental disabilities. Some, but not all,

of theconditionsseemtohavehighva- lidity(seeBouletetal2 formoredetail.) Ongoing survey research is needed to maintain the validity of the survey questions,whilebalancingthebenefits of historical information to compare overtime. Finally, although we as- sumed that many of these conditions are chronic, in fact, a condition may resolve to the point where parents or health care providers may no longer consider the child ashaving thedisor- der. Recent evidence13,39 of this was found for autism, and a longitudinal studyshowedconsiderablechanges in diagnoses over time for children with physical andemotional orbehaviordi- agnoses. Finally, some children in- cludedinthestutteringorstammering or seizures categories may have had transient conditions, resulting in an overestimation of the prevalence of these conditions.

CONCLUSIONS

We found that the number of children withdevelopmental disabilitieshas in- creased over the decade. These find- ingshaveadirect bearingon theneed for health, education, and social ser- vices, including theneed formorespe- cializedhealthservices (mentalhealth services, medical specialists, thera- pists, andalliedhealth professionals). Also, the consequent burden on fami- liesandcaregiverswillneedtobecon- sidered. Finally,moredetailedstudyof the influence of risk factor shifts, changes inacceptance,andbenefitsof early services isneeded tobetterun- derstand why these shifts have occurred.

ACKNOWLEDGMENTS The National Health Interview Study is supported by the Centers for Disease ControlandPrevention,Atlanta,Georgia.

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(Continued fromfirst page)

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Copyright©2011by the American Academyof Pediatrics

FINANCIALDISCLOSURE: Theauthors have indicated that they have nopersonal financial relationships relevant to this article to disclose.

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DOI: 10.1542/peds.2010-2989 ; originally published online May 23, 2011; 2011;127;1034Pediatrics

Blumberg, Marshalyn Yeargin-Allsopp, Susanna Visser and Michael D. Kogan Coleen A. Boyle, Sheree Boulet, Laura A. Schieve, Robin A. Cohen, Stephen J.

2008 −Trends in the Prevalence of Developmental Disabilities in US Children, 1997

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2008 −Trends in the Prevalence of Developmental Disabilities in US Children, 1997

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