Prevalence, Patterns, and Persistence of SleepProblems in the First 3 Years of Life

WHAT’S KNOWN ON THIS SUBJECT: Sleep problems are commonduring childhood, but screening for sleep problems in the clinicsetting is often cursory. Moreover, there are few longitudinalstudies examining the prevalence and persistence of sleepproblems in young children.

WHAT THIS STUDY ADDS: Patterns of sleep problems vary acrossearly development, but sleep problems arising in infancy persistin 21% of children through 36 months of age. Parent response toa nonspecific query about sleep problems may overlook relevantsleep symptoms and behaviors.

abstractOBJECTIVE: Examine the prevalence, patterns, and persistence ofparent-reported sleep problems during the first 3 years of life.

METHODS: Three hundred fifty-nine mother/child pairs participatedin a prospective birth cohort study. Sleep questionnaires wereadministered to mothers when children were 6, 12, 24, and 36months old. Sleep variables included parent response to anonspecific query about the presence/absence of a sleep problemand 8 specific sleep outcome domains: sleep onset latency, sleepmaintenance, 24-hour sleep duration, daytime sleep/naps, sleeplocation, restlessness/vocalization, nightmares/night terrors, andsnoring.

RESULTS: Prevalence of a parent-reported sleep problem was 10% atall assessment intervals. Night wakings and shorter sleep durationwere associated with a parent-reported sleep problem duringinfancy and early toddlerhood (6–24 months), whereas nightmaresand restless sleep emerged as associations with report of a sleepproblem in later developmental periods (24–36 months). Prolongedsleep latency was associated with parent report of a sleep problemthroughout the study period. In contrast, napping, sleep location, andsnoring were not associated with parent-reported sleep problems.Twenty-one percent of children with sleep problems in infancy(compared with 6% of those without) had sleep problems in thethird year of life.

CONCLUSIONS: Ten percent of children are reported to have a sleepproblem at any given point during early childhood, and these problemspersist in a significant minority of children throughout early develop-ment. Parent response to a single-item nonspecific sleep query mayoverlook relevant sleep behaviors and symptoms associated withclinical morbidity. Pediatrics 2012;129:e276–e284

AUTHORS: Kelly C. Byars, PsyD,a,b Kimberly Yolton, PhD,c

Joseph Rausch, PhD,b Bruce Lanphear, MD, MPH,d andDean W. Beebe, PhDb

Divisions of aPulmonary Medicine, bBehavioral Medicine andClinical Psychology, and cGeneral and Community Pediatrics,Cincinnati Children’s Hospital Medical Center, Cincinnati, Ohio;and dFaculty of Health Sciences, Simon Fraser University andChild and Family Research Institute, British Columbia Children’sHospital, Vancouver, British Columbia, Canada

KEY WORDSsleep problems, infants, toddlers, prevalence, persistence

ABBREVIATIONOSA—obstructive sleep apnea

Each author made a substantive intellectual contribution to thestudy. Dr Byars participated in early conceptualization anddesign of sleep measurement methodology and collaboratedwith coauthors on data interpretation; he took a lead role withdrafting and revising the article. Dr Rausch provided criticalcontributions to formulating the data analytic plan and assistedwith data interpretation as well as reviewing and revising thearticle for important intellectual content. Dr Yolton wasa primary investigator in the research laboratory that securedfunding for this project. She had primary responsibility for thestudy design and oversight of its execution and participated inthe conceptualization and design of the sleep measurementtools. Dr Yolton also played a significant role with respect todata collection and interpretation as well as critically reviewingand revising the article. Dr Lanphear was the principalinvestigator who secured funding for this project. He hadprimary responsibility for the study design and oversight of itsexecution. Dr Lanphear also played a significant role withrespect to data collection and interpretation as well as criticallyreviewing and revising the article. Dr Beebe also participated inearly conceptualization and design of sleep measurementmethodology, conducted data analysis and interpretation ofstudy findings, and drafted and critically revised the article.

www.pediatrics.org/cgi/doi/10.1542/peds.2011-0372

doi:10.1542/peds.2011-0372

Accepted for publication Sep 26, 2011

Address correspondence to Kelly C. Byars, PsyD, Divisions ofPulmonary Medicine and Behavioral Medicine and ClinicalPsychology, Cincinnati Children’s Hospital Medical Center, ML2021, 3333 Burnet Ave, Cincinnati, OH 45229-3039. E-mail: Kelly.Byars@cchmc.org

PEDIATRICS (ISSN Numbers: Print, 0031-4005; Online, 1098-4275).

Copyright © 2012 by the American Academy of Pediatrics

FINANCIAL DISCLOSURE: The authors have indicated they haveno financial relationships relevant to this article to disclose.

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Sleep problems are common in child-hood andmay persist if not adequatelymanaged.1–5 The importance of de-tection and treatment of pediatricsleep disorders is underscored by agrowing literature that links sleepproblems with other morbidities.6–15

For example, cardiovascular morbidityand metabolic syndrome have beenlinked with obstructive sleep apnea(OSA).9,10 Sleep problems are also as-sociated with impairments in daytimefunctioning and decreased quality oflife in affected children6,7,11–15 as wellas secondary effects on families (eg,disrupted parent sleep; marital dis-cord; maternal stress).16–20

Because sleep is essential to dailyfunctioning, sleep is routinelyaddressedthrough anticipatory guidance in pe-diatric settings.21 However, researchindicates that pediatric sleep problemsmay go undetected during routine clin-ical care.22–24 In a survey of pedia-tricians it was revealed that roughly halfdo not screen for sleep disturbance oruse singular screening questions whentalking with parents of infants and tod-dlers (eg, “Does your child have anysleep problems?”23). Furthermore, littleis known about how parents interpretand report sleep problems. Thus super-ficial inquiry and parent interpretationabout what constitutes a sleep problemare factors that likely play a role inthe underdiagnosis or misdiagnosis ofpediatric sleep problems. For example,clinically important symptoms such assnoring, a hallmark symptom of OSA,might be missed if they are not en-compassed within parents’ typical defi-nitions of a “sleep problem.” Further,once a sleep problem is identified, thedecision to intervene rests in part uponthe physician’s belief about whether theproblem will persist. The bulk of theliterature supports the persistence ofearly-onset sleep problems2–5,25–35 buthas relied on nonspecific dichotomousmeasures or focused on a narrowly

defined sleep behavior (eg, bedtimerefusal). Few authors have seriallymeasured a comprehensive measureof parent-reported sleep patterns dur-ing early childhood.

Clinical decision-making may be ham-pered by gaps in our knowledge of theutility of a nonspecific single sleepscreening question and the prevalenceand persistence of sleep problemsduring early childhood. The purpose ofthe current study was to fill these gapsby examining the prevalence, patterns,and persistence of broadly definedsleep problems and more specificdomains of sleep behavior during thefirst 3 years of life.

METHODS

Sample

The study cohort comprised mother/child pairs participating in the HealthOutcomes and Measures of the Envi-ronment Study, an ongoing prospectivebirth cohort in the Cincinnati, Ohio,metropolitan area.36 Beginning inMarch 2003, women were identifiedfrom 7 prenatal clinics associated with3 hospitals. Eligible mothers wereidentified at #19 weeks of gestation,were age $18 years, negative for HIV,and not taking medications for seizureor thyroid disorders. Letters weremailed to 5184 prospective subjects; 468of the 1263 eligible respondents wereconsented and enrolled. Sixty-sevenenrollees dropped out before delivery;3 children were stillborn. Nine sets oftwins were excluded because theirsleep arrangements could fundamen-tally differ from those of singleton chil-dren. Thirty (8%) of the 389 women withsingleton live births did not completesleep questionnaires, resulting in a finalsample of 359 subjects.

Procedures

The institutional review board of Cin-cinnati Children’s Hospital MedicalCenter provided oversight for the

study. All mothers provided written in-formed consent before enrollment.Enrollees received phone calls regu-larly tomaintain contact and interest inthe study. Study assessments werecompleted annually during clinic andhome visits, and telephone surveyswere conducted at the 6-month mid-point each year.

Sleep Questionnaire

Questionnaires were administered viastructured interviews by trained re-search assistants by telephone whenthe children were 6 months of age.Face-to-face interviews were con-ducted during a home visit when thechildren were 12, 24, and 36 months ofage. There is no gold standard for sleepassessment that spans infancy andearly childhood, so 2 questionnaireswere developed based upon previousvalidated sleep instruments. Thequestionnaire for 6- to 12-month-oldsincluded 26 items adapted from severalscales,26,37–41 whereas the question-naire for 24- to 36-month-olds included53 items adapted from the Child SleepHabits Questionnaire.42 Both ques-tionnaires included the nonspecific di-chotomous item “Do you think ____(child’s name) has problems sleeping?”Because this is similar to the singlequestion that is often asked in pedia-tricians’offices, the response comprised1 of our key outcomes: “nonspecific sleepproblem.”

The questionnaires were not direct-ly parallel because developmentalchanges necessitated differences initem content (eg, sleepwalking itemsare not relevant for infants) and therange of response options. Conse-quently, we were not able to directlycompare every sleep behavior acrossall time points. Instead, we first defineddevelopmentally relevant sleep behav-ior domains based upon the previoussleep literature and subsequentlyidentified specific questionnaire items

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representative of these sleep domains.The sleep behavior domains and theircomposition were refined based uponan examination of item variability andfactor analyses from each time point.The final item content for the 8 domainsis presented in Table 1 (see Supple-mental Information for responseoptions and endorsement patterns ateach time point). Items had differingresponse options, so we convertedeach item’s response set to a common zscore metric relative to the cohortmean and SD at each time point. Formulti-item domains, individual itemscores were averaged before furtheranalyses. The result was a matrix ofcontinuous domain scores for eachsubject at each time point that (a) wasconceptually consistent over time, (b)was placed on a common statistical

metric, and (c) mirrored the dis-tributions of the raw data.

Statistical Analysis

Preliminary x2 and Mann-Whitney Utests compared the demographiccharacteristics of subjects with avail-able sleep data at each time pointagainst those with missing data to as-sess for differential attrition over time.These tests and Spearman correla-tions also examined whether the sleepdomain scores or rate of overall sleepproblems differed reliably by childgender, family income, or race. Finally,using Fisher’s z test, we examinedwhether the correlations described inour primary analyses varied signifi-cantly by race or gender. Finding nosubstantive difference in the pattern ofcorrelations among the subgroups, we

subsequently used the full sample forprimary analyses.

Wecalculated frequencydata forparentreport of a nonspecific sleep problemat the 6-, 12-, 24-, and 36-month as-sessments. We also examined which ofthe 8 sleep behavior domains wereassociated with parent report of asleep problem at each time point. Wecalculated Spearman correlations todetermine the association between con-tinuous sleep behavior domain scoresat each time point with analogousscores obtained later. Finally, to de-termine the risk for persistence ofparent-reported sleep problems, wecalculated odds ratios and associatedFisher’s exact tests. A two-tailed signifi-cance threshold of P, .05 was adoptedacross all analyses.

TABLE 1 Sleep Domains, Interpretation, and Item Composition

Scale Name Meaning of a High Score Items Included in 6- to 12-Month Assessments(Timeframe: “On average, over the past month”)

Items Included in 24- to 36-Month Assessments(Timeframe: “During a typical week”)

Sleep onset latency Falls asleep quicklyand easily

After the bedtime routine (eg, bath),how long does it take to get ___ to sleep at night?

How often does ___ …

How many times per week have you had problemsgetting ___ to sleep at night?

…fall asleep within 20 min after going to bed?

…resist going to bed at bedtime?…struggle at bedtime (eg, cry, refuse tostay in bed)?

How often is ___ ready to go at bedtime?Sleep maintenance Few night wakings How many… How often does ___ wake up…

…nights per week has ___ woken during sleep? …once during the night?…times has ___ woken each night? …more than once during night?

24-h sleep duration Longer sleep How much time does ___ spend… What is ___’s usual amount of sleep each day,combining nighttime sleep and naps?

…sleeping each night?…napping each day?

Naps More daytime naps How many… How often does ___ nap during the day?…days per week has ___ napped during the day?…naps has ___ taken per day?

Sleep location Sleeping in own bed/crib Where is ___ initially laid down to sleep?(data collapsed to parent bed versus not)

How often does ___ fall asleep…

Where has __ slept most of the night?(data collapsed to own bed/crib versus not)

…alone in his or her own bed?

…in a parent’s or sibling’s bed?Restlessness andvocalization

Calm, quiet sleep How many nights per week have youseen or heard ___

How often…

…talking or vocalizing during sleep? …does ___ talk or vocalize during sleep?…being restless or moving around during sleep? …is__ restless and moving a lot during sleep?

Nightmares/nightterrors

Few events How many nights per week have you seenor heard __ wake up sweating,screaming, and inconsolable?

How often does ___ …

…awaken during the night and is sweating,screaming, and inconsolable?

…awaken alarmed by a frightening dream?Snoring Minimal snoring How many nights per week have you seen

or heard ___ snoring loudly during sleep?How often does ___ snore loudly?

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RESULTS

Demographics

Of the 359 eligible mother/child dyads,sleep data were available for 342 (95%)at6months, 335(93%)at12months, 280(78%) at 24months, and 258 (72%) at 36months. Demographic characteristicsare summarized in Table 2. The sample,which was evenly divided by gender,was comprised primarily of first- andsecond-born children and coveredbroad socioeconomic strata. At the 6-month survey point, the sample was64% white participants and 31% Afri-can American participants. There wasdifferential attrition over time amongAfrican Americans and those in thelowest education and income groups(P , .005).

African American children and thosefrom lower-income families werereported to have longer sleep onsetlatency, shorter overall sleep duration,less independent sleep, and moresnoring than were white children andthose fromhigher-income familiesat alltime points (P , .01; SupplementalTables 5 and 6). However, the overallrate of parent-reported nonspecificsleep problems and behaviors aroundsleep maintenance did not significantlydiffer by race or family income at anytime point. Reported napping/daytimesleep, vocalization/restlessness, andnightmares/night terrors differed by

race or family income at only 1 timepoint each. Sleep variables differed bychild gender in only 3 of 36 analyses,well within expectations based uponchance variation alone.

Prevalence and Patterns ofParent-Reported Sleep Problems

As shown in Fig 1, the presence of anonspecific sleep problem was repor-ted by roughly 10% of parents at eachtime point. Parent report of a sleepproblem was significantly associatedwith longer sleep onset latency acrossall age ranges, as well as poorer sleepmaintenance and shorter sleep dura-tion at 6 to 24 months but less stronglyat 36 months (Table 3). Nightmares/night terrors and restlessness/vocalization were significantly associ-ated with parent report of a sleepproblem from 12 to 36 months of age.Parent report of a sleep problem wassignificantly associated with snoringonly at 12 months and with the locationof a child’s sleep only at 24 months. Thefrequency of naps or daytime sleep wasnever significantly associated with pa-rental report of a sleep problem.

Stability of Sleep-Related Behaviorsand Parent-Reported SleepProblems

Table 4 presents correlations betweensleep domain scores obtained at each

time point with the equivalent domainscore collected at later time points.Medium (r = 0.30) to large (r = 0.50)effects43 were observed for nearly allcorrelations from 1 time point to thenext, and significant correlationswere evident between our 2 mostdistant measurement points (6 and36 months) in sleep onset latency, sleepduration, sleep location, restlessness/vocalization, and snoring.

Compared with those who were notreported to have an early sleep prob-lem, infants and toddlers with a repor-ted sleep problem had much higherrates of such problems at later timepoints (Figs 2, 3, and 4). Only 6% to 8%of children without a reported sleepproblem at 1 time point developed sucha problem later. In contrast, 21% to 35%of those who were reported to havea sleep problem during early childhoodshowed persistent sleep problems 1 to2 1/2 years later.

DISCUSSION

Prevalence and Patterns of SleepProblems

Our findings indicate that the overallprevalence of parent-reported sleepproblems remains stable during earlydevelopment. At each time point, 1 in10 parents reported the presence ofa sleep problem in response to a single,nonspecific screening question that

TABLE 2 Sample Demographics

Total Sample 6 mo 12 mo 24 mo 36 mo

Sample size, n 359 342 335 280 258Age, mean 6 SD, mo NA 6.4 6 0.5 12.9 6 1.2 25.1 6 1.0 37.3 6 1.5Gender, % girls 55 55 55 54 54Race, % white% African American

64 65 66** 70*** 71***31 30 28 24 24

Parity (median [25th,75th percentile])

1 (0, 1) 1 (0, 1) 1 (0, 1) 1 (0, 1) 1 (0, 1)

Maternal education at birth(median years [25th,75th percentile])

16(14, 16)

16(14, 16)*

16(14, 16)***

16(14, 16)***

16(14, 16)**

Family income at birth(median in $1000s [25th, 75thpercentile])

50 000–60 000(25–30, 80–90)

50 000–60 000(25–30, 80–90)

50 000–60 000(25–30, 80–90)**

60 000–70 000(30–40, 80–90)***

60 000–70 000(30–40, 80–90)**

Demographic differences between retained and missing subjects via x2 or Mann-Whitney U test, *P , .05, **P , .01; ***P , .001. NA, not available.

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is similar to what many physiciansuse during routine clinic visits.22–24

This falls well within the broad rangeof reported prevalence rates (2%–33%) based on cross-sectional re-search.4,25–27,30,31

There appear to be developmentalshiftsover thefirst 3 yearsof life inwhatparents mean when they report a non-specific sleep problem. Our data sug-gest that sleep onset difficulties are

considered problematic by parentsthroughout early childhood, consistentwith previous studies documentingthat this is a common complaint ofparents with young children.5,25,29,33

Our findings also suggest that nightwakings and shorter sleep durationwere perceived as sleep problems by6 months of age and then remainedparticular concerns for parents through2 years of age. In contrast, parental

endorsement of a sleep problem wasnot linked to sleep behaviors char-acteristic of partial arousal para-somnias (ie, nightmares/terrors;vocalizations/restlessness duringsleep) until 12 to 36 months of age.

Parents who reported that their childhad a sleep problem did not reportatypical snoring, sleep location, ornapping/daytime sleeping behaviorsduring early childhood. It is noteworthythat the failure of a parent to recognizeand report problems related to thesedomains could lead to errors in clinicaldecision making. For example, 12% to20% of our sample snored multiplenights per week, placing them at highrisk for OSA, a nocturnal breathingdisorder associated with medical mor-bidity and neurobehavioral deficits inchildren.44 However, parents did notseem to associate snoring with sleepproblems, and previous research hasshown that routine screening forsnoring occurs in only 25% or less ofwell-child visits.42 As a result, snoringcould be completely overlooked duringwell-child visits, despite its known riskfor morbidity. The American Academyof Pediatrics recommends that allchildren be specifically screened forsnoring and that children deemedat risk for OSA be referred for sub-specialty evaluation.44

Sleeping arrangements, particularlyinfant sleep location, has receivedconsiderable attention in the pediatricliterature.45–49 Cosleeping is on the risein North America and other indus-trialized countries and is an acceptedand common practice in many ethnicgroups.46–48 In our study, data for sleeplocation were collapsed to examinesolitary sleeping versus sleeping inother contexts (eg, parent’s/sibling’sbed). Across all time points, the ma-jority of children (62.5%–81.9%) weresleeping in their own bed; infants andtoddlers 16.6% and 17.2%, respec-tively, were sleeping with a parent. Our

FIGURE 1Prevalence of parent-reported sleep problems. Percent of children reported by their parent to havea sleep problem at 6, 12, 24, and 36 months of age.

TABLE 3 Associations between Parental Endorsement of an Overall Sleep Problem and SleepDomain Scores

6 mo 12 mo 24 mo 36 mo

Sleep onset latency 20.23*** 20.22*** 20.20** 20.31***Sleep maintenance 20.27*** 20.29*** 20.31*** 20.15*24-h sleep duration 20.16** 20.17** 20.23*** 20.13*Naps/daytime sleep 20.01 0.03 20.04 20.04Sleep location 20.06 20.03 20.18** 20.11Restlessness/vocalization 20.07 20.13* 20.24*** 20.24***Nightmares/night terrors 20.07 20.20*** 20.31*** 20.21**Snoring 20.09 20.15** 20.04 20.08

Two-tailed point-biserial correlation significance: *P , .05, **P , .01, ***P , .001.

TABLE 4 Correlations of Sleep Domain Data Collected at 6, 12, and 24 Months With the SameDomain at Later Time Point(s)

Correlation of Data at 6 MoWith That Collected Later at…

Correlation of 12-MoData With Data Collected at…

Correlation of 24-MoData With Data From

…12 mo …24 mo …36 mo …24 mo …36 mo …36 moSleep onset latency 0.35*** 0.17** 0.19** 0.39*** 0.24*** 0.41***Sleep maintenance 0.34*** 0.13* 0.11 0.16** 0.17** 0.20**24-h sleep duration 0.44*** 0.30*** 0.29*** 0.35*** 0.20** 0.37***Naps 0.17** 20.09 0.00 0.07 0.20** 0.33***Sleep location 0.50*** 0.33*** 0.29*** 0.55*** 0.42*** 0.66***Restlessness andvocalization

0.34*** 0.23*** 0.19** 0.32*** 0.27*** 0.32***

Nightmares/nightterrors

0.10 0.12 0.09 0.22*** 0.03 0.18*

Snoring 0.37*** 0.19** 0.23*** 0.31*** 0.23*** 0.29***

Two-tailed significance values for Spearman rank-order correlations: *P , .05, **P , .01, ***P , .001.

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findings suggest that parents do notsystematically consider the sleep loca-tion of their 6- to 36-month-old child tobe, in and of itself, a problem. Sleep lo-cation may be more relevant in the

context of specific sleep symptoms/behaviors. For example, night wakingsmay be considered more problematicto parents if they cosleep with theirchild. Future research examining sleep

location in the context of prevalence andpersistence of pediatric sleep problemsshould consider more refined analysesof specific sleep symptoms/behaviors(eg, breastfeeding; smoking exposure)that were not a focus of this study.

Finally, our study findings contrast withanecdotal evidence indicating that pa-rents of young children struggle withnap issues (eg, irregular nap sched-ule).45 Our data show that parents ofinfants and toddlers do not systemati-cally relate napping behavior to thepresence of a sleep problem; if a clini-cian is interested in learning about nap-ping, specific queries are necessary.

Stability of Sleep Problems andSleep Behaviors

Our findings provide guidance topediatricians about the persistence ofsleepproblems in youngchildren.Whencomparedwithnonproblemsleepers atthe same age, children reported bytheir parents to have a sleepproblematany time point in early childhood hada three- to fivefold greater risk for latersleep problems. In our data, 23% to 35%of children who were reported to havea sleepproblemat 6, 12, or 24months ofage went on to also have a similarproblem at later measurement points.These observations are generally con-sistent with other longitudinal studiesthat have documented the persistenceof infant onset sleep problems in 30% to40% of children through 36 months ofage.4,25,26 Thus, although the majority ofinfants and toddlers identified as hav-ing a sleep problem at any given timeare not identified as having such aproblem later, a significant minoritycontinue to have problems over spansof months to years.

We also examined the stability of morespecific domains of sleep behavior (eg,sleepduration, sleep location, snoring),allowing for3broad inferences. First, asmightbeexpected, sleepdomainscoresmeasured closer in time correlated

FIGURE 2Persistence of parent-reported sleep problems. Percent of childrenwith a sleep problemat 6months ofage (open bars) versus without a sleep problem at 6 months (black bars) who went on to have a sleepproblem at later time points. OR, odds ratio. Significance values from Fisher’s exact test: *P, .05, **P,.01, ***P , .001.

FIGURE 3Persistence of parent-reported sleepproblems. Percentof childrenwith asleepproblemat 12monthsofage (open bars) versus without a sleep problem at 12 months (black bars) who went on to have a sleepproblem at later time points. OR, odds ratio. Significance values from Fisher’s exact test: *P, .05, **P,.01, ***P , .001.

FIGURE 4Persistence of parent-reported sleepproblems. Percentof childrenwith asleepproblemat 24monthsofage (open bars) versus without a sleep problem at 24 months (black bars) who went on to have a sleepproblemat 36months of age. OR, odds ratio. Significance values from Fisher’s exact test: *P, .05, **P,.01, ***P , .001.

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more strongly than those collected overlonger time spans, suggesting partic-ular stability in sleep behaviors across6- to 12-month time spans. Second,there was generally moderate stabilityin sleep behaviors over time, with thegreatest stability in sleep behaviorstending to be in the domains of sleeponset latency, sleep duration, sleep lo-cation, restlessness/vocalization, andsnoring. Thus, parent-report in theseareas cannot be expected to changemarkedly across the infant and pre-school years. In contrast, daytimesleep/naps, nightmares/terrors, andnocturnal arousals were less stableover time. Finally, significant corre-lations between our 2 most distantmeasurement points (6 and 36months) in sleep onset latency, sleepduration, sleep location, restlessness/vocalization, and snoring suggest thatthese sleep behaviors, or at leastparent-report of these behaviors, mayestablish themselves quite early indevelopment.

Study Limitations

There are several study limitations thatshould be considered when interpret-ing our results. First, sampling errormay have influenced prevalence esti-mates of sleep problems; approxi-mately one third of eligible respondentscompleted baseline study proceduresand approximately one fourth of theoriginal sample was lost to attrition bythe final follow-up interval. Additionally,in light of the sampling methodologyinvolving recruitment from prenatalclinics in metropolitan Cincinnati, Ohio,results may not be applicable to the

general population of children acrossNorth America. Second, all sleep mea-sures were based on parent-report,and although this is likely to be theprimary source of information in theclinic, rater bias cannot be ruled out.Third, since there is no single validatedinstrument for assessing sleep prob-lems inchildrenaged6 to36months,wewere required to pool data from 2 in-dependent sleep questionnaires. Wetook steps in our statistical analyses toensurecomparability of data, and itwasreassuring that the correlations be-tween behavior domain scores col-lected at 12 and 24 months (spanningthe infant and preschool question-naires) were similar to those between6 and 12 months or between 24 and 36months (within a given questionnaire).Nevertheless, measurement impreci-sion could have been introduced by thelack of parallel measures at all as-sessment points. Fourth, because thesleep problem and behavioral domainsthat were the focus of this study areculturally defined to varying degrees,the potential impact of cultural differ-ences in defining sleep problems mustbe considered. Our analyses indicatedthere were differences between themajority and minority groups with re-spect to several domains of sleepbehaviors. However, there were nodifferences in the prevalence and per-sistence of sleep problems betweengroups and thus the cultural differ-ences did not appear to havemateriallyinfluenced our study findings. Finally,this descriptive study did not pro-pose nor examine potential mecha-nisms underlying sleep problems.

Consequently, we did not consider po-tential confounding variables duringdata analysis. Future investigationsexamining the persistence of sleepproblems should consider underlyingmechanisms and potential confoundingvariables.

CONCLUSIONS

Parent interpretation and report ofa sleep problem during early childhoodmay be inconsistent with clinical cri-teria for diagnosing pediatric sleepdisorders, especially when assessedvia a nonspecific query. To clarify pa-rental concerns about sleep duringearly development and ensure thatclinically relevant sleep issues are notoverlooked, we recommend that sleepproblems be screened by using a flexi-ble family-centered approach whileaddressing specific sleep behaviorsand symptoms that have known clinicalsignificance. Owens and Dalzell50 havedeveloped a tool that has proven utilityin the clinic setting, facilitates briefsleep screening, is developmentallysensitive, and is behavior/symptomspecific. Although we did not directlytest the utility of that tool, the currentstudy confirms the importance of fo-cused screening for sleep problemsduring infancy and early childhood thatgoes further than merely asking if thechild has problems sleeping.

ACKNOWLEDGMENTThis work was partially supported bygrants from the National Institute of En-vironmental Health Sciences (R01ES015517-01A1, P01 ES11261).

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