Developmental screen or developmental testing? Samantha Johnson * , Neil Marlow 1 Academic Division of Child Health, E Floor, East Block, Queen’s Medical Centre, Nottingham, NG7 2UH, United Kingdom Abstract Given the high risk for residual disability in preterm infants, outcome monitoring is a crucial function of neonatal care. Provision of neurodevelopmental follow-up to at least 2 years of age corrected for prematurity forms part of national recommendations for neonatal services. This should include a developmental assessment at 2 years to identify disability. Although screening tools are cost and time efficient measures, they are not diagnostic and have less utility in high-risk populations. In contrast, standardised developmental tests are ideally suited for follow-up purposes and have become widely accepted as outcome measures. We highlight the properties of standardised tests and review the most commonly used tools for assessment in infancy. We also outline a number of practical issues in the use of standardised tests with preterm infants in identifying morbidity and predicting later impairment. Parental reports are also discussed and key guidelines for developmental testing at 2 years are provided. D 2006 Elsevier Ireland Ltd. All rights reserved. 0378-3782/$ - see front matter D 2006 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.earlhumdev.2006.01.008 * Corresponding author. Tel.: +44 115 8230609; fax: +44 115 8230626. E-mail addresses: [email protected] (S. Johnson)8 [email protected] (N. Marlow). 1 Tel.: +44 115 8230605; fax: +44 115 8230626. KEYWORDS Preterm; Outcome; Developmental assessment; Standardised test; Reliability; Validity; Prediction Contents 1. Introduction......................................................... 174 2. The need for early outcome monitoring ......................................... 174 2.1. Why monitor long-term outcome? ........................................ 174 2.2. When is it optimal to assess developmental outcome? ............................. 174 2.3. How should developmental outcome be assessed? ............................... 175 3. Characteristics of standardised developmental tests .................................. 175 3.1. Test objectivity ................................................... 175 3.2. Norm-referenced scores .............................................. 175 3.3. Psychometric properties .............................................. 175 3.4. Test selection .................................................... 176 4. Standardised developmental tests for infants ...................................... 176 4.1. Commonly used tests of development in infancy ................................ 176 4.2. Mullen Scales of Early Learning (MSEL) ...................................... 176 4.3. Battelle Developmental Inventory II (BDI-II) ................................... 178 Early Human Development (2006) 82, 173—183 available at www.sciencedirect.com www.elsevier.com/locate/earlhumdev
Transcript
ava i l ab l e a t www.sc i enced i r ec t . com
www.e l sev i e r . com/ loca te /ea r l humdev
Developmental screen or developmental testing?
Samantha Johnson *, Neil Marlow 1
Academic Division of Child Health, E Floor, East Block, Queen’s Medical Centre, Nottingham, NG7 2UH, United Kingdom
0378-3782/$ - see front matter D 200doi:10.1016/j.earlhumdev.2006.01.008
1. Introduction. . . . . . . . .2. The need for early outcome
2.1. Why monitor long-ter2.2. When is it optimal to2.3. How should developm
3. Characteristics of standardis3.1. Test objectivity . . .3.2. Norm-referenced sco3.3. Psychometric propert3.4. Test selection . . . .
4. Standardised developmenta4.1. Commonly used tests4.2. Mullen Scales of Early4.3. Battelle Developmen
Abstract Given the high risk for residual disability in preterm infants, outcome monitoring is acrucial function of neonatal care. Provision of neurodevelopmental follow-up to at least 2 yearsof age corrected for prematurity forms part of national recommendations for neonatal services.This should include a developmental assessment at 2 years to identify disability. Althoughscreening tools are cost and time efficient measures, they are not diagnostic and have lessutility in high-risk populations. In contrast, standardised developmental tests are ideally suitedfor follow-up purposes and have become widely accepted as outcome measures. We highlightthe properties of standardised tests and review the most commonly used tools for assessment ininfancy. We also outline a number of practical issues in the use of standardised tests withpreterm infants in identifying morbidity and predicting later impairment. Parental reports arealso discussed and key guidelines for developmental testing at 2 years are provided.D 2006 Elsevier Ireland Ltd. All rights reserved.
Early Human Development (2006) 82, 173—183
6 Elsevier Ireland Ltd. All rights reserved.
8230609; fax: +44 115 8230626.ttingham.ac.uk (S. Johnson)8 [email protected] (N. Marlow).5 8230626.
Infants born preterm are at greater risk for developmentalimpairments than term peers. Given the high risk for residualdisability, and the poor prediction of long term outcome fromneonatal course, the monitoring of long term morbidity is acritical function of neonatal care. Standardised develop-mental assessments are ideally suited to the identification,quantification, and monitoring of children with developmen-tal difficulties. In this paper we highlight the need for earlyoutcome monitoring, review briefly the standardised assess-ment tools available for use in infancy, and highlight anumber of issues pertaining to their use in the follow-up ofpreterm infants throughout the first 2 years of life.
2. The need for early outcome monitoring
2.1. Why monitor long-term outcome?
It is increasingly well documented that preterm birth mayhave adverse effects on a child’s development. Significantdisabling conditions that are clearly associated with pretermbirth, such as severe visual and hearing impairments andcerebral palsy (CP), have been shown to range from 15% to20% at threshold viability with marked consistency over thelast decade [1,2]. However, increasing evidence suggeststhat the most common area of poor functioning is within thedomain of cognition. Compared to classmates, 41% ofextremely preterm children aged 6 years have IQ scores inthe moderate to severely impaired range (scores �2 S.D.),and a further 31% have mild cognitive impairment (scores�1 to �2 S.D.) [3]. Consistent trends also show that IQscores are inversely related to gestational age, with boys atgreater risk for impairment than girls. Preterm children arealso at greater risk for more subtle longer term deficits inattentional, perceptual-motor, and visuo-spatial abilities,which may be present in as many as 50% to 70% of VLBWchildren [4], and are more likely to have scores in theimpaired range on tests of behavioural competence [5] andeducational achievement [6]. This is mirrored in earlychildhood with developmental impairment being the mostcommon finding at 2 years [2].
The prediction of individual outcome from neonatalcourse remains extremely poor, not least because social andenvironmental factors interact to affect outcome following
discharge. Monitoring long term outcome in NICU graduates istherefore a crucial function of a neonatal service for:
! informing current clinical management,! early identification of children at risk for later difficulties,! instigating and monitoring intervention strategies,! service audit,! monitoring the prevalence of poor outcome followingperinatal care,
! evaluating the long-term efficacy of perinatalinterventions,
! identifying perinatal markers of poor longer-term func-tioning to enable early prediction of adverse problems,
! informing the ethical debate regarding the treatment ofbabies born at borderline viability.
The identification and quantification of developmentalimpairment in infancy, and the prediction of later disability,are thus important goals for neonatal follow-up services.
2.2. When is it optimal to assess developmentaloutcome?
National recommendations for standards for hospitals pro-viding neonatal services [7] advise that neurodevelopmentalfollow-up should be continued up to at least 2 years of agecorrected for prematurity, and that standardised guidelines[8] for identifying disability should be used to definefunctional health status at this age.
Although development may be monitored sequentiallyover the first 2 years, repeated testing may reveal widelydiffering scores throughout this period that representrandom variation in performance across testing sessionsrather than the elucidation of an underlying developmentaltrajectory, even in a child who has evolving disability [9].Developmental assessment tools also provide strict guide-lines as to the inter-test interval for the administration ofrepeated assessments in order to attenuate the influence ofpractice effects. Assessments administered at 2 yearscorrected age may optimise early identification of disability.A number of conditions commonly associated with pretermbirth are not evident or resolved until approximately 2 years(e.g., CP, transient dystonia) [10]. Thus it may be expedientto conduct a comprehensive developmental assessment atthis age.
Developmental screen or developmental testing? 175
2.3. How should developmental outcome beassessed?
For whole-population surveillance programmes developmen-tal screening tools are used to identify individuals who areat risk for unsuspected deviations from normal develop-ment. Although these measures are cost and time efficient,they have less utility in inherently high risk populations.Optimising the accuracy of early assessment is particularlyimportant for the identification of subtle developmentaldelays and mild impairments that may result in moreintrusive conditions at school age. Screening tools havelittle diagnostic utility, particularly for identifying suchsubtle impairments, as a result of their construction asdfirst-lineT measures to identify individuals who will requiremore detailed assessment. As prematurity is a clear medicalrisk factor for developmental impairment, preterm infantswill routinely require more thorough assessments and thusthe use of screening measures is essentially redundant insuch a population. More diagnostic and comprehensivemeasures are required to accurately assess outcome inpreterm infants. For these purposes, standardised devel-opmental tests provide detailed assessments from which weare able to accurately discriminate abnormality andquantify the extent of developmental difficulties in thispopulation.
3. Characteristics of standardised developmentaltests
3.1. Test objectivity
Standardised tests are psychometric measures designed toinventory an individual’s abilities and provide a comparisonbetween his/her performance on the test with that of thenorm (i.e., that which would be expected for a child of his orher age). Specifically, standardised developmental tests aredesigned to assess a child’s global developmental level byproviding an inventory of key developmental milestones.Additionally, in some tests, it is possible to obtain anassessment of an individual’s abilities within specificdevelopmental domains.
Standardised assessments in general comprise formaltester-administered measures in which a qualified examineradministers the test adhering to a stringent administrationand scoring protocol. To the untrained observer these testsmay seem rather rigid or harsh, but the strict administrationrules serve to optimise the objectivity of the results, somuch so that deviation from the prescribed protocolinvalidates use of the test scores. The objectivity of thesetests makes them ideal for large-scale use, such as routinefollow-up, in which multiple examiners may administer thetest and in which comparisons are made between the resultsof individuals or groups.
For clinical use an examiner may wish to test the limitsof a child’s abilities by administering items above or belowthose required for the standardised administration. Thisapproach is useful in producing a qualitative profile ofdevelopment of relative strengths and weaknesses and forinstructional planning. However, the results of such assess-ments should be reported using qualitative or descriptive
classifications or using developmental age equivalents asstandardised scores cannot be derived if the examiner hasdeviated from the standardised administration (also seeSection 5.4).
3.2. Norm-referenced scores
During standardisation, a test is administered to a largegroup of children for whom it is designed; this group formsthe normative sample or dnormal populationT. An indivi-dual’s score obtained on the test is essentially a comparisonto this normative data and is used to determine how s/he isdeveloping in relation to the norm. Standardised tests thusyield norm-referenced or standardised scores. Standardisedscores are age-adjusted scores with a normalised distribu-tion and prescribed Mean and S.D. For developmentalmeasures, standardised scores typically have a Mean of100 and S.D. of 15, in keeping with most other psychometricassessments. Other types of standardised scores include Tscores (Mean 50, S.D. 10), Scaled scores (Mean 10, S.D. 3),and z Scores (Mean 0, S.D. 1). For test interpretation theS.D. essentially becomes the unit of measurement: thedeviation of an individual’s score from the mean of thenormative sample, in terms of standard deviation bands, isused to classify his/her developmental level. (E.g., a childwith a score �2 S.D. is typically classified as havingsignificantly delayed performance, see Section 5.2).
Standardised tests may also yield other norm-referenced scores (e.g., Percentiles, Age Equivalents),but these should be reviewed only after derivation of thestandardised scores. Although age equivalent scores areoften used to aid reporting of test results to caregiversthese can be problematic. Children with developmentalages below their chronological age may actually havedevelopment within the normal range of standardisedscores. Standardised scores should thus be the principalunit of analysis for test interpretation and classification ofdevelopmental level.
3.3. Psychometric properties
During construction, standardised tests are subject todetailed empirical analyses to assess the psychometricproperties of the scale, namely:
i. Normative sample: sample of the dnormal populationTfor which the test is designed.! Representativeness: the extent to which the norma-tive sample is an accurate reflection of the normalpopulation for whom the test is designed. This maybe maximised by systematic sampling procedures,such as stratification by age group to ensureaccurate representation of gender, ethnic group,geographical location, parental education, etc., incomparison to the national population, often de-fined using national census data.
! Size: the larger the overall sample, and at each ageband, the more accurately comparisons can be madewith the norm at all ages.
ii. Reliability: the extent to which a test yields the sameresults when administered repeatedly.
S. Johnson, N. Marlow176
! Internal consistency: the correlation between itemswithin a scale.
! Test—retest reliability (Repeatability): the correla-tion between scores obtained by the same examineradministering the test on several occasions to thesame child.
! Inter-rater reliability: the correlation betweenscores obtained by two different examiners scoringthe same test administered to the same child.
iii. Validity: the extent to which a test measures what itpurports to measure.! Content validity: whether the test contains arepresentative sample of the abilities it is designedto measure.
! Construct validity: whether the test measures theunderlying theoretical constructs or traits it isdesigned to measure.
! Concurrent validity: the correlation between scoresobtained on the test with scores obtained on anotherwell-validated bcriterion measureQ administered atthe same time.
! Predictive validity (Predictability): the correlationbetween the scores obtained on the test with scoresobtained on a criterion measure administered at alater time point. Information on predictive validitymay be less well documented given the length oftime required to collect longitudinal data.
The standardisation of a test itself does not necessitatepsychometric integrity: the reliability, validity, and rigour ofthe standardisation process can vary widely between tests.In general, the better the psychometric properties of a testthe more valid and reliable, and thus accurate, conclusionscan be drawn about an individual’s developmental level.
Additionally, the time of standardisation of a test canhave important consequences for test interpretation. TheFlynn Effect [11] refers to the upward drift in standardisedscores over time. Although originally identified as relating toIQ scores, a similar effect has been shown with standardisedscores on developmental tests illustrating that a child’sdevelopmental level may be over-estimated if older norma-tive data are applied [12]. In the EPICure Study, aprospective cohort study of outcome following extremeprematurity, 21% of 6-year-old children achieved scores inthe moderate to severely impaired range (scores �2 S.D.)compared to the norms of the IQ test published in 1981.When a more contemporary comparison was made againstscores obtained on the test by matched classmates assessedsimultaneously, the number of children classified as moder-ate to severely impaired rose to 41% [3]. The more recentlya test is developed, the more likely it is to contain test itemsthat are based on current empirical studies and methods ofassessing development, and to reflect current theories ofchild development.
3.4. Test selection
When selecting a standardised developmental test oneshould first consider whether the test applies to the agerange for which it will be used. Although a number of testsare designed for use with children aged 24 months and
above, their use in preterm infants at 2 years corrected ageis not advisable: 2 years is usually the lowest detectableperformance for such a test and establishing a basal level ofperformance or extent of delay may be difficult in impairedpopulations. Tests designed specifically for use throughoutinfancy are more applicable for the assessment of preterminfants at 2 years corrected age.
When selecting a measure one should review informationregarding its psychometric properties that is typicallyprovided in the test manual. A test with sound psychometricproperties and recent standardisation should be selected.Clinicians may use measures that have face value in theirdiscipline, and with which they have prior experience, inorder to test specific clinical hypotheses, even if such testshave less inspiring psychometric properties. It may also beexpedient to consider using tests selected by other profes-sionals to aid uniformity across services and to facilitatecross-disciplinary discourse.
Standardised developmental tests can be costly. They aretypically supplied as whole units comprising the instructionmanual, manipulatives, and record forms, and can beexpensive to purchase. The majority of publishers alsoproduce scoring software that accompanies the test butmust often be purchased at an additional cost. Thestandardised record forms must also be used as photocopy-ing is strictly prohibited, and such tests can only be used andpurchased by examiners with the relevant qualifications.However, such costs are necessary: use of the genuinestimulus materials is essential for standardisation, and thenecessarily high user qualifications serve to protect theaccurate interpretation of test results and the integrity ofthese tests.
4. Standardised developmental tests for infants
4.1. Commonly used tests of development ininfancy
The most commonly used standardised developmental testscomprise:
1. Mullen Scales of Early Learning (MSEL) [13]2. Battelle Developmental Inventory II (BDI-II) [14]3. Griffiths Mental Development Scales—Revised (Griffiths
Scales) [15]4. Bayley Scales of Infant Development II (BSID-II) [16].
The characteristics of these tests are summarised inTable 1, and a brief review of each scale is presented inSections 4.2—4.5 in order to aid test selection.
4.2. Mullen Scales of Early Learning (MSEL)
The MSEL are a combination of the original Infant MSEL andPreschool MSEL that provide a measure of the Fine Motor,Visual Reception, Receptive Language, Expressive Language,and Gross Motor skills in children from birth to 68 months. TScores, percentiles, and age equivalents are derived foreach sub-test and an Early Learning Composite (ELC)standardised score can be obtained as a measure of global
Table 1 Characteristics of the most commonly used standardised developmental tests for infants
Test Age range Administration
time
Domains assessed Standardisation
years
Sample Norm-referenced
scores
User qualifications
Mullen Scales of Early
Learning (MSEL)
Birth through
5 years 8 months
1 year olds:
15 min; 3 year
olds: 30 min
Gross Motor (V33 months)
Fine Motor
Visual Reception
Receptive Language
Expressive Language
1981—1986 and
1987—1989
1849 USA Standardised T scores (Mean
50, S.D. 10), percentiles,
and age equivalents for
each domain.
Training and/or experience
in clinical assessment of
young children.
The 4 cognitive sub-scales
combine to produce an
Early Learning Composite
(ELC) standardised score
(Mean 100, S.D. 15),
percentile, and age equivalent.
Battelle Developmental
Inventory II (BDI-II)
Birth to 8 years 1—2 h Personal—Social
Adaptive Motor
Communication Cognitive
(plus sub-domains)
2002—2003 2500 USA Standardised scores
for sub-domains (Mean
10, S.D. 3), domains
(Mean 100, S.D. 15), and
composite DQ (Mean 100,
S.D. 15), z-scores, percentiles,
and age equivalents.
Psychologists and
dParaprofessionalsT (e.g.,preschool, primary, special
needs teachers).
Griffiths Mental
Development
Scales—Baby Scales
(Griffiths Scales: 0—2)
Birth through
23 months
35—60 min Locomotor
Personal—Social
Hearing and Language
Eye and Hand Coordination
Performance
(Not stated) 665 UK Standardised scores for each
domain (Sub-quotients, SQ,
Mean 100, S.D. 16), age
equivalents, and percentiles.
Psychologists or clinicians
with training in developmental
assessment. Examiners
must undergo a 5-day
training course for
certification.
Sub-scale scores combine to
provides standardised score
(General Quotient, GQ, Mean 100,
S.D. 12), age equivalent, and
percentiles for overall functioning.
Bayley Scales of Infant
Development, 2nd
Edition (BSID-II)
1 month through
42 months
25—60 min Mental (MDI)
Psychomotor (PDI)
Test-taking behaviour (BRS)
1991—1992 1700 USA Standardised scores for MDI and PDI
(Mean 100, S.D. 15), percentiles
and age equivalents.
Professional qualification
in individual assessment;
experience in testing
young children.Percentiles only for BRS.
Deve
lopmental
screenordeve
lopmental
testin
g?177
S. Johnson, N. Marlow178
cognitive functioning. It is quick to administer in comparisonto other instruments and requires examiners to haveprofessional training in developmental assessment. It pro-vides a good profile of a child’s strengths and weaknesseswithin the domain of cognition.
Whilst the psychometric properties of the scale areadequate, the normative data, having been standardisedsome 15 and 23 years ago, are now outdated in comparisonto other tests. Whilst the test also provides a detailedassessment of a child’s early cognitive abilities, the ELC doesnot reflect gross motor functioning and the Fine Motor sub-test is based on a small number of items. The test thus hasless utility for preterm infants in whom significant motorimpairment might be expected. This test is rarely used as acontemporary outcome measure in this population.
4.3. Battelle Developmental Inventory II (BDI-II)
The BDI-II, a revision and re-standardisation of the originalBDI, became available for purchase at the time of prepara-tion of this paper. This second edition retains the structureof the first edition providing an assessment of developmentin the domains of Personal—Social, Adaptive, Motor, Com-munication, and Cognition, in children from birth through8 years. User qualifications of the BDI-II are lower than othertests. It can be administered by individuals without profes-sional training in developmental assessment thus extendingthe range of health professionals who may administer thetest. Interpretation of results should, however, be carriedout by trained professionals. The full kit can be purchasedwithout the manipulatives required for test administration.However, whilst this reduces the cost of the test itintroduces a potential source of bias.
The test yields scaled scores, percentiles, and ageequivalents for sub-domains, and additional standardisedscores for domains and for overall functioning (DQ: Mean100, S.D. 15). It provides a profile of development and istherefore particularly useful for instructional planning andmonitoring intervention efficacy. In contrast to other tests,the BDI-II contains guidelines for adaptations to testadministration for individuals with physical, visual, orhearing impairments that can be applied without compro-mising the normative value of the test.
Reported limitations of the first edition include a lack ofinformation regarding the psychometric properties of thescale, particularly at the sub-domain level, concern re-garding the small number of items in some sub-domains,the relatively small normative sample, and the possibilityof floor effects with standardised scores extending onlydown to 65, this latter limitation being a particularproblem for use in high risk populations. The BDI-IIaddresses these limitations. The number of items in thesub-domains has been expanded at all ages and the rangeof standardised scores for domains and for the DQ has beenextended to 40—160. The psychometric properties of thetest have reportedly been improved in order to meet orexceed standards for psychometric scales. Crucially, theBDI-II has been very recently standardised on a largernormative sample (n =2500) closely matching the 2000 UScensus, thus providing representative contemporary refer-ence data.
Despite the provision of a comprehensive profile ofdevelopment, and improvements in this recent revision,the utility of the BDI-II as a contemporary outcomemeasure may be limited. Clinicians and researchers maycontinue to use a tool they are familiar with and that haspreviously become established as a conventional measure.It is unlikely to supersede more commonly used measuresfor neonatal follow-up, particularly as revisions of otherpopular tests are also currently available (Sections 4.4and 4.5).
4.4. Griffiths Mental Development Scales—Revised(Griffiths Scales)
The Griffiths Scales comprise the bBaby ScalesQ for childrenfrom birth through 23 months, and the bExtended ScalesQ forchildren from 24 months to 8 years. Here we review theBaby Scales as that most applicable for use throughout thefirst 2 years.
The Baby Scales require approximately 45 min toadminister and provide an assessment of functioning infive domains: Locomotor, Personal—Social, Hearing andLanguage, Eye and Hand Coordination, and Performance.The test yields standardised scores (Mean 100, S.D. 16) foreach domain and a composite General Quotient (Mean 100,S.D. 12). Like the BDI-II, this scale provides a profile ofdevelopment and analysis of strengths and weaknesses.The test may only be administered by professionals withexperience in developmental assessment and examinercertification requires attendance at a 5-day trainingcourse. The test can be purchased in the UK from the TestAgency and is the least costly of the measures reviewedhere.
Notably, the Griffiths Scales is the only test standardisedin the UK. The Baby Scales have also undergone a necessaryand timely revision and re-standardisation. Whilst thenormative sample is large for an infant test, with 665children aged 0—24 months, the standardisation itself is lessimpressive and lacks methodological rigour. The samplelacks detailed comparison to UK census statistics, and maynot be wholly representative of the population from which itis drawn. The scale’s psychometric properties are alsopoorly detailed. Test—retest reliability is particularly poorfor the first year, and information regarding inter-scorerreliability and validity is not provided.
A less considered difficulty with the Griffiths Scales liesin their use at 2 years—the crucial age for follow-up. Whilstthe Baby Scales are designed for use with children 0—2years, and the Extended Scales for children from 2 to8 years, they are not directly comparable not having beenco-normed. The extended scales include a sixth sub-scale(Practical Reasoning), and either scale must be usedseparately as both produce separate GQs based on differentnormative data sets. One is left with the question ofpotential problems establishing a basal performance onthe extended scales, particularly for preterm children whoperform below population means, and encountering ceilingeffects for high achievers assessed after 2 years of age usingthe Baby Scales.
Despite these limitations the Griffiths Scales remain oneof the most popular developmental tests for follow-up and
Developmental screen or developmental testing? 179
research purposes, particularly in the UK and Europe. As therevised scales are yet in their infancy, a body of evidenceregarding their psychometric properties should naturallyevolve and may serve to strengthen their utility as anoutcome measure.
4.5. Bayley Scales of Infant Development II (BSID-II)
The BSID-II is the most widely used standardised develop-mental test, in particular for research purposes both in theUK and the US. It is designed to assess Mental (Cognitive;MDI) and Psychomotor (PDI) development in infants aged 1to 42 months. A third bBehaviour Rating ScaleQ (BRS) isincluded on which the examiner rates qualitative aspects ofthe child’s test taking behaviour. The BRS is rarely usedexperimentally, but can be useful in facilitating theinterpretation of test results. The test can be lengthy toadminister, particularly for children with disordered ordelayed development, and requires that examiners haveprofessional training and experience in assessment. It can bepurchased from Harcourt Assessment and is one of the mostcostly of the tests outlined here.
The BSID-II yields standardised Index scores and ageequivalents for the MDI and PDI. Developmental ages mayalso be derived post-hoc for 4 sub-scales or dfacetsT.However, these are infrequently used in practice and therehas been much criticism of the BSID-II for its lack of sub-scale standardised scores and for the construction and theinclusion of few items in its facets. In contrast, thestandardisation of the BSID-II is the most impressive of thetests. The normative sample is large (1300 children aged 0through 24 months alone), representative of the USpopulation, and rigorously sampled with stratification byage. Psychometric properties of the scale are also adequate,with moderate to high correlations for various measures ofreliability and criterion-referenced validity, although thetest may further benefit from additional informationregarding predictive validity.
Due to the recognition of the BSID-II as a valuableoutcome measure and clinical tool, a body of evidence hasaccumulated regarding the utility of the scale since itspublication in 1993. This has resulted in a large literatureexamining the limitations of the scale. Such reportedlimitations include the lack of separate standardisedscores for non-verbal performance, particularly whentesting children with specific language or hearing impair-ments. A particular criticism lies in the unconventionalstructure of the test. Age-related sets of test items areadministered in which basal and ceiling limits (lower andupper limits on a child’s performance) are satisfied by theachievement of a cumulative (rather than the convention-al consecutive) number of item passes and fails. This isbased on the assumption that development proceeds in anordinal sequence. However, when assessing populations inwhom development may be delayed or disordered theiruse can be problematic, particularly given the compre-hensive nature of the two scales (i.e., the MDI failing toprovide separate assessments of non-verbal and languageabilities, and the PDI comprising both gross and fine motormeasures). For example, a child with advanced languagemay achieve a ceiling on non-verbal items and thus obtain
an MDI that does not reflect his/her linguistic skills.Similarly, a child with spastic diplegia (CP) may satisfy abasal limit on fine motor items and thus receive a PDIwithin the normal range that does not reflect his or hergross motor disability.
More specific to the present population, concerns havebeen levelled at the use of corrected age and thecorresponding selection of item sets and norm tables forchildren born preterm. This is because testing and inter-pretation based on chronological and corrected age canresult in different index scores [17]. Although this continuesto be a contentious issue, when assessing preterm infants achild’s corrected age should be used to determine both thetest entry point and the corresponding norm table. Relatedcriticisms have also been levelled at the use of the itemsets. As the test requires entry at the child’s chronologicalage, establishing the basal and ceiling limits for a child withdevelopmental delays can result in the administration of alarge number of items ultimately drawn from beyond thestarting item set. However, if testing begins at a moreappropriate estimated developmental age for children withimpairments, this may ultimately result in an under-estimation of ability and differing index scores for item setsfrom the starting one to that corresponding to the child’schronological age [18].
These shortcomings may seem numerous, but theirquantity is a consequence of the test’s widespread useand popularity as a sound outcome measure. Such criti-cisms do not necessarily compromise the test if one isaware of such limitations when administering and, partic-ularly, when interpreting the test. The BSID-II remains amost popular choice as an outcome measure and itswidespread use has enabled meta-analyses and cross-disciplinary discourse, an essential element of outcomeassessment.
Importantly, a timely and much anticipated revision andre-standardisation of the scales (the Bayley Scales of Infantand Toddler Development III, Bayley-III) was released at thetime of preparation of this paper and is available fromHarcourt Assessment from November 2005. The publishersreport that the test will provide a more comprehensiveassessment of children aged 1 to 42 months. It will comprisefive sub-scales to assess cognition, language, motor skills,social—emotional, and adaptive behaviour that will yieldScaled scores, and composite standardised Index scores.This may thus ameliorate problems associated with the lackof standardised scores for cognitive vs. language skills, andgross vs. fine motor skills. The test will also benefit fromextended floors and ceilings thus permitting an assessmentof development at lower functioning levels and for moreimpaired children and populations. The manual will also beexpanded to contain data on clinical populations. Thepsychometric properties and standardisation of the test alsoclaim to be as impressive as the BSID-II with good validityand reliability and a large representative normative sample.Interestingly, the publishers suggest that the Bayley-III willultimately be standardised in the UK for the first time. Therevision of this popular test may address some of thelimitations and reported problems of the BSID-II, and studieswill undoubtedly ensue in the upcoming years to investigatethe utility of the test with children with both typical andatypical development.
S. Johnson, N. Marlow180
5. Practical issues in assessment of preterm infants
5.1. Corrected age
There has previously been debate regarding the use ofcorrected age in assessing the development of preterminfants, largely due to the potential for over estimatingdevelopmental level when it is applied. However, theconsensus today is to correct for prematurity when assessingchildren born b32 weeks, or of VLBW, particularly duringinfancy when the effects of preterm birth are more signifi-cant. Although there is less agreement about the age at whichto cease correction, it is recommended that correction beapplied up to at least 2 years of age [8]. This may be extendedfor children born extremely preterm (or of ELBW) as adevelopmental quotient obtained through assessments basedon chronological and corrected age may produce a clinicallysignificant difference up to 3 years of age.
5.2. Classification of abnormality
The classification of abnormality should be defined usingstandardised scores. Specifically, the deviation of an indivi-dual’s score from that of the normative mean is used toclassify developmental impairment:
! scores within 1 S.D. of the mean are classified as withinnormal limits
! scores �1 S.D. to �2 S.D. are classified as having mildimpairment
! scores more than 2 S.D. below the mean (typically scoresb70) are classified as having moderate (�2 to �3 S.D.) tosevere (b�3 S.D.) impairment.
To date, this has certainly been the consensus foridentifying children with impairment. However, a consensusstatement has suggested that a cut-off of �3 S.D. may bemore predictive of later poor performance—see Section 5.5.
5.3. Quantifying severe developmental impairment
Standardised scores typically range from 50 to 150. This maypresent a problem in quantifying the extent of impairmentin children whose development is significantly impaired ordelayed. If an individual child’s score falls outside the rangeof the test, the presence of impairment can be ascertainedbut the extent of this impairment cannot be quantified. Thiscan be problematic in cases in which group mean scores arerequired, as floor effects may be encountered when usingthe test in high risk populations. For clinical purposes this isalso problematic for the monitoring of developmentalprogress or the efficacy of intervention efforts as smallgrowth increments cannot be detected within this range.
For statistical analyses, it is imperative to distinguishbetween a score obtained at the lowest range of scores(e.g., 50 in BSID-II) and one that should represent lowerlevels of functioning below the range of the test (typicallyscores �3 S.D.). For these purposes, scores below the rangeof a test can be assigned a nominal value (e.g., 39) to reflecta score obtained more than 3 S.D. below the Mean. Specific
to the BSID-II, it is possible to derive standardised indexscores within the range of 30 to 50 using extrapolated norms[19], although caution should be observed when usingextrapolated scores as these are statistically rather thanempirically derived. It is also possible to calculate adevelopmental quotient (DQ) to facilitate statistical analy-ses and clinical interpretation of test results.
5.4. Assessing children with disabilities
Assessing children with perceptual or physical disabilitiescan be problematic when using standardised tests. Makingadaptations to the test stimuli (e.g., using larger blocks tofacilitate grasping in a child with CP), to the administrationof test items (e.g., allowing additional response time ontimed items), or to the scoring procedures (e.g., acceptingcaregiver report as a substitute for direct observation) inorder to minimise the impact of a child’s disability on his/her performance may be useful for assessing the limits of achild’s abilities and for developing intervention. However, inthe vast majority of tests, such adaptations are notpermitted: if adaptations are made these compromise thenormative value of the test and, as such, the norm-referenced and standardised scores should not be derived.
With exception, the BDI-II provides guidelines for adapta-tions of the test for use with children with disabilities thatcan be made without forfeiting application of the testnorms. For children with hearing or language impairments,it may also be expedient to use a test that provides separatestandardised scores for verbal and non-verbal sub-tests(e.g., Griffiths Scales, BDI-II), rather than the BSID-II whichis particularly problematic for testing children with lan-guage impairments given the lack of a separate non-verbalscore.
Similar problems may be encountered when using astandardised test with children in whom English is not afirst language. Such children will have low scores onstandardised tests, particularly on language items on whichthe examiner cannot directly translate instructions orresponses his or herself. In cases in which the examiner isunable to communicate directly in the child’s language,whether it be a different spoken language or a signedlanguage, permitting caregiver translations introduces apotential source of bias in testing. Again, it may beexpedient to use a test that provides separate verbal andnon-verbal scores with non-English speaking children.
Ultimately, the administration of a standardised test witha child with a perceptual or physical disability should behypothesis driven. For the purposes of obtaining standar-dised scores in order to compare developmental levelbetween individuals and groups, the test should be admin-istered in the standardised manner, even if this may seemcumbersome or harsh. In order to assess an individual child’sabilities and test the limits of their performance to provide amore qualitative profile of development, the test may beadapted, but standardised scores should not be derived.
5.5. Predictive validity
Whilst the central focus of developmental follow-up lies inthe accurate assessment of outcome, the ultimate goal is
Developmental screen or developmental testing? 181
the elucidation of early predictors of later disability. Thepredictability of infant tests is of particular importance.
It is well accepted that developmental tests havegenerally poor predictive validity for later IQ, and academicachievement. The predictive validity of neonatal examina-tions and early infant tests are notoriously poor, particularlyin normally developing populations. Reasons for this lack ofpredictability have centred around measurement errorinherent in infant tests, the differences between the skillsassessed by early developmental tests and later measures ofIQ/information processing and educational outcome, intra-individual change in cognitive function over time, and theinteraction of medical, environmental, and social factors inchildhood that may influence development. The predictivevalidity of infant tests is better in clinical populations,particularly for children with significant neurological im-pairment and those with developmental delays. The predic-tive validity of developmental tests may be increased by adecreasing inter-test interval and by assessment after2 years during which time self-righting processes in infancyare attenuated and the effects of the environment haveincreasing influence [20].
More recently, researchers have turned their attentionto developing tests that focus on specific areas ofinformation processing in infancy (e.g., the Fagan Testof Infant Intelligence) to improve continuity with skillsassessed in later IQ measures, and these tests may resultin improved prediction from tests administered in infancy.However, these measures are typically experimental innature and have rarely been subjected to the rigorouspsychometric assessments of conventional standardisedmeasures.
A standardised developmental score less than 2 S.D.below the mean is conventionally used to classify disability(Section 5.2). In a recent study of ELBW children assessedwith the BSID-II at 20 months and the Kaufman AssessmentBattery for Children (K-ABC) [21] at 8 years of age, theapplication of a cut-off b70 resulted in a reduction in theprevalence of disability over time [22]. Eighty percent ofchildren without neurosensory abnormalities who scoredb70 on the BSID-II achieved scores in a higher classificationon the K-ABC at 8 years, resulting in a very poor positivepredictive value. The positive predictive validity of a scoreb70 was improved for children with neurosensory abnor-malities, indicating greater stability in cognitive scores forthis severely impaired group. The vast majority of ELBWchildren with scores N70 at 20 months also achieved higherscores on the K-ABC, thus resulting in a high negativepredictive value. It should be noted, however, that althoughthe majority of children with scores b70 at 20 months haveimproved scores at 8 years, many may still have significantimpairment with scores remaining below the normal range.Thus whilst a BSID-II score b70 may not accurately catego-rise later severe abnormality, it should be recognised as arisk factor for later impaired functioning, perhaps mostnotably for more subtle impairments that may exacerbateschool failure.
Although properties of the tests used may have contrib-uted to the improvement in scores over time, othercontemporary data provides evidence to suggest that alower cut-off might be appropriate for the prediction ofdisability. A consensus statement has suggested that scores
b3 S.D. may be more appropriate [8] for classification ofsevere disability. There is also evidence that such aclassification may be more predictive of a later disability.In the EPICure Study, a national cohort study of theoutcomes of birth b26 weeks, BSID-II MDI scores �3 S.D.were highly predictive of moderate to severe cognitiveimpairment (K-ABC scores b70) at 6 years of age [3].
The classification of severe disability in infancy using acut-off score �3 S.D. may be optimal for predicting latersevere disability and impaired IQ. However, children withscores in the range �2 S.D. to �3 S.D. should also beidentified as being at-risk for later learning difficulties andpoor outcome. Given the generally poor predictivevalidity for individual outcome, prediction might beoptimised for clinical management by considering envi-ronmental and social risk, and by sustained follow-upthrough childhood, particularly for those with mildlydelayed performance in infancy who may be susceptibleto later subtle impairments.
6. Parental measures of development
Standardised developmental tests can be costly and timeconsuming, particularly for large scale follow-up. A poten-tial alternative lies in the use of parental reports. Parentalquestionnaires are quick and easy to complete, are cost andtime efficient, and require little time to score and interpret.Although there is concern regarding the use of parentalreports, these may provide relatively accurate assessmentsif a measure is well constructed with proven reliability andvalidity.
Parent report questionnaires more commonly used withpreterm infants include:
! Ages and Stages Questionnaires (ASQ) [23]! Parents’ Evaluation of Developmental Status (PEDS) [24]! Minnesota Child Development Inventory (MCDI) [25]! Kent Inventory of Developmental Skills (KIDS) [26]! Parent Report of Children’s Abilities Revised for PretermInfants (PARCA-R) [27].
Parent reports are typically screening measures designedto identify children in need of further diagnostic assessmentand, as a result, primarily yield cut-off scores or norm-referenced scores such as age equivalents or DQ’s. Withexception, the KIDS yields standardised scores for fivedevelopmental domains and for overall functioning.
The Parent Report of Children’s Abilities (PARCA) [28] is aparental assessment of cognitive and language developmentin 2-year-olds. We have recently modified and validated thisquestionnaire—PARCA-R—for particular use as an outcomemeasure for very preterm infants (b30 weeks) [27]. This hasgood concurrent validity and diagnostic utility for predictionof an MDI score b70. This has proven a useful tool forassessing cognitive development at 2 years for very pretermchildren; it is currently used in several large national andinternational randomised trials, and is included in theplanning for a range of new studies.
Caution should be observed when using parental mea-sures. These can be useful when time and costs are limited,for example, in large scale epidemiological studies and
S. Johnson, N. Marlow182
randomised trials, and are useful in promoting parent—professional discourse. However, parent reports should notreplace a formal developmental assessment which should beused whenever possible.
7. Conclusion
Long-term neurodevelopmental follow-up of preterminfants is of critical importance for neonatal services.Assessing developmental outcome at 2 years of agecorrected for prematurity seems to be the optimalcompromise for the accurate identification of impairmentand for routine outcome monitoring in infancy. Althoughscreening tests would provide a cost and time efficientmethod of assessing development in clinics, these onlyidentify children in need of further assessment and arethus less useful for impaired populations a large propor-tion of whom will need more detailed diagnosticassessment.
Although costly and time consuming, standardised devel-opmental tests are the Gold Standard for outcome assess-ment. These provide objective, valid, and reliableassessments of an infant’s development in comparison tothe norm, and standardised scores from which classificationsof developmental level can be made. The Griffiths Scalesand the BSID-II are the most commonly used standardiseddevelopmental tests in infancy and recent revisions of thesescales may serve to further strengthen their popularity.Whilst professionals may use other tests for assessingspecific hypotheses, or parent reports as a cost and timeefficient alternative, a well constructed standardised testwith sound psychometric properties should be used wher-ever feasible.
Given the poor predictive validity of infant tests, longerterm follow-up should ideally be instigated. Whilst studieshave shown that scores �3 S.D. may be more predictive ofsignificant disability, children with mild impairments shouldalso be considered at risk for later difficulties. Thesechildren may suffer subtle deficits that might result in moreintrusive conditions in later childhood and contribute to theimpaired scholastic performance often observed in childrenborn preterm.
8. Key guidelines
! Neurodevelopmental follow-up over the first 2 years oflife should include a developmental assessment tomonitor outcome in preterm infants.
! Assessments administered at 2 years of age corrected forprematurity optimise the accuracy of identification ofimpairment in infancy.
! Standardised developmental tests are the Gold Standard,from which standardised scores are used to classifydevelopmental impairment.
! Griffiths Scales and BSID-II are the most popular standar-dised infant tests.
! Parental report measures can be useful alternatives, butshould only be used where a standardised test is notfeasible.
! Given the poor predictive validity of infant tests longer-term follow-up would be ideal.
9. Research directions
! The ultimate goal of developmental follow-up remainsthe elucidation of early predictors of later disability.
! To further assess the predictive validity of infantdevelopmental test scores for later intellectual andeducational functioning.
! To develop focused measures of infants’ abilities thathave good predictive validity for later intellectualfunctioning.
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