Screening Cognitive Abilities in Adults with Developmental Disabilities: Correlations of the K-BIT,...

P1: HAA/HGI P2: GLB/fzi QC: GLB

Journal of Developmental and Physical Disabilities [jodd] PP506-374605 June 20, 2002 11:4 Style file version June 18th, 2002

Journal of Developmental and Physical Disabilities, Vol. 14, No. 3, September 2002 ( C© 2002)

Screening Cognitive Abilities in Adults WithDevelopmental Disabilities: Correlations of theK-BIT, PPVT-3, WRAT-3, and CVLT

Shawn Powell,1,4 Roger Plamondon,2 and Paul Retzlaff 3

A screening battery composed of the K-BIT, PPVT-3, WRAT-3, and CVLTwas administered to a population of adults with developmental disabilitiesresiding in an intermediate care facility/mental retardation. The cognitiveareas investigated were general ability, receptive vocabulary, achievement, andverbal memory. Of primary interest were the correlations between these in-struments when administered to this population. The correlations between theK-BIT, PPVT-3, and WRAT-3 were direct and strong, ranging from .72 to.98, whereas the correlations between these tests and the CVLT were directand moderate, ranging from .45 to .69. These findings support the convergentvalidity of the K-BIT, PPVT-3, and WRAT-3, and the divergent validity of theCVLT when administered to adults with developmental disabilities.

KEY WORDS: cognitive assessment; developmental disabilities; mental abilities.

Advances in medical and behavioral treatments have resulted in longerlife span for many individuals with developmental disabilities (Braddock,1999; Miezejeski et al., 2000). Consequently, many of these individuals areliving long enough to experience declines in cognitive performance anddementia (Devenny et al., 1996). To better understand the implications oflonger life span in individuals with developmental disabilities, and to as-sist in maturational treatment planning, attention has been directed towardmeasuring the cognitive processes of adults with developmental disabilities

1United States Air Force Academy, Colorado.2Children’s Hospital, Behavioral Health, Birmingham, Alabama.3University of Northern Colorado, Greeley, Colorado.4To whom correspondence should be addressed at Dept. of Behavioral Sciences and Leadership,Cheyenne, Wyoming.

239

1056-263X/02/0900-0239/0 C© 2002 Plenum Publishing Corporation



240 Powell, Plamondon, and Retzlaff

(Burt et al., 1998). Efforts to measure the cognitive effects of habilitation forthis population as they age have also been undertaken (Lifshitz and Rand,1999) and an emerging literature suggests that some declines in cognitivefunctioning may be ameliorated (Gedye, 1998).

One rationale for conducting cognitive assessments is screening forfunctional changes (Dikmen et al., 1999). In performing individual diagnos-tic assessments, clinicians are encouraged to use information from multiplesources rather than relying on the results of a single test (Donders, 1999;Sattler, 1992). Screening batteries composed of different instruments de-signed to measure various aspects of cognitive functioning can assist clini-cians in making such determinations. Brief screening measures have beenused to assess various cognitive functions and to identify various disorders(Lovejoy et al., 1999). Additionally, in the era of managed care, economicalapproaches to treating and assessing individuals with developmental disabil-ities have been considered (Kastner et al., 1997; Walsh and Shenouda, 1999).

There are numerous benefits associated with cognitive screening.Among the benefits of screening batteries is the sampling of a variety of cog-nitive domains in a brief period of time. Second, screening batteries allow forthe economical use of resources. This permits comprehensive assessmentsto be reserved for individuals whose screening battery results suggest thepresence of serious deficits. In this way, individuals whose results suggestnormal functioning may be spared unnecessary evaluation. Third, screen-ing procedures can identify an individual’s strengths and weaknesses acrossvarious cognitive domains. This permits the results of a screening batteryto be used to formulate remedial and habilitation recommendations for thedomains measured. Fourth, a well-designed screening battery may be usedto chart longitudinal data across several cognitive domains. This can facili-tate the identification of dementia and other cognitive declines, as adequatebaseline information is available for future comparison (Albert and Cohen,1992; Gedye, 1995).

In adults with developmental disabilities, measurable aspects of cogni-tive functioning include general ability, vocabulary, academic achievement,and verbal memory. The relationships of general ability, vocabulary, andacademic achievement have been extensively explored in the literature (seeKaufman and Kaufman, 1990b; Sattler, 1992; Williams and Wang, 1997).However, the relationship of these constructs to verbal memory has not beenwidely studied. Common assessment instruments of general ability, vocab-ulary, academic achievement, and verbal memory respectively include theKaufman Brief Intelligence Test (K-BIT; Kaufman and Kaufman, 1990a),Peabody Picture Vocabulary Test – Revised (PPVT-R; Dunn and Dunn,1981), Wide Range Achievement Test – Revised (WRAT-R; Jastak andWilkinson, 1984), and the California Verbal Learning Test (CVLT; Deliset al., 1987).



Correlations of the K-BIT, PPVT-3, WRAT-3, and CVLT 241

Correlations between these measures for individuals with and withouthandicapping conditions have been reported. For example, Childers et al.(1994) found a correlation of .75 between the K-BIT Composite score andthe PPVT-R for a group of preschool students. Smith et al. (1991) reportedthat correlations between the PPVT-R and the WRAT-R ranged from .33 to.42 for a sample of school children referred for academic difficulties. Correla-tions between the K-BIT Composite score and the subtests of the WRAT-Rranged from .34 to .69 for various adult groups (Kaufman and Kaufman,1990b).

Although research on the K-BIT, PPVT-R, and WRAT-R is readilyavailable in the literature, reports on the relationship of these tests to theCVLT is sparse. Verbal memory appears to operate relatively independentlyof other cognitive processes and does not typically correlate highly withother cognitive measures, such as general ability, vocabulary, and academics(Boone et al., 1998). The assessment of verbal memory can yield uniqueinformation about an individual (McIntosh et al., 1997). Thus, as a construct,verbal memory appears to be an important and unique cognitive processwarranting assessment (Dikmen et al., 1999; Paniak et al., 1998) and hasbeen investigated in individuals with mental retardation (McDaniel et al.,1998).

As a population’s variance and covariance can largely impact a test’scharacteristics, research into the characteristics of tests for specific popula-tions has been called for (Dikmen et al., 1999; Golden et al., 1999; Holland andOliver, 1995). Toward this end, this investigation examined the relationshipsof the K-BIT, PPVT-3 (Dunn & Dunn, 1997), WRAT-3 (Wilkinson, 1993),and CVLT when used to assess adults with developmental disabilities.

METHODS

Participants

Participants were 30 adults with developmental disabilities residing ina state-operated intermediate care facility/mental retardation. The sampleincluded 10 females and 20 males ranging in age from 18 to 49 years(M = 36 years, Mdn = 37 years). This group included individuals from thefollowing racial and ethnic groups: African American (1), Caucasians (27),Hispanic (1), and Native American (1). In terms of mental retardation clas-sifications 2 participants were within the borderline range, 19 were withinthe mild range, 6 were within the moderate range, 2 were within the severerange, and 1 was in the profound range. The participants’ cognitive func-tioning levels were taken from the latest psychological reports contained intheir individual files.




Measures

The screening instruments used in this study were four brief measuresof cognitive functioning. The domains measured, and tests administeredwere (a) intellectual ability—K-BIT, (b) receptive vocabulary—PPVT-3,(c) academic achievement—WRAT-3, and (d) verbal memory—CVLT. Theevaluators were two psychology doctoral level candidates completing theirinternships.

Procedure

To safeguard the participants’ rights the institution’s human rights com-mittee reviewed and approved the proposed study prior to participant con-tact. The following inclusion criteria were established: (a) age 50 or less,(b) no diagnosis of dementia, (c) no sensory impairments, and (d) adequatevisual, verbal, and motor functions to complete the tests. Parents or guardiansof the facility’s residents who met these criteria were sent a letter describingthe study and requesting their consent for participation. After written con-sent was obtained from parents or guardians, the participants gave writtenassent to take part in the study, which was explained in developmentallyappropriate terms. The first 30 individuals who met the inclusion criteria,and for whom consent and assent for the study was obtained, served asparticipants.

After participants provided their written assent to take part in thestudy, they completed the screening battery in a single session. To controlfor order effects, the four tests were given in counterbalanced sequence.All testing procedures were administered in a standardized fashion withoutmodification.

Results from the screening battery were correlated using the PearsonProduct–Moment Correlation Coefficient formula. For the K-BIT, PPVT-3,and WRAT-3 total raw scores were used. For the CVLT the total number ofwords recalled on the first five trials was the score used for the correlations.

RESULTS

The participants’ K-BIT Composite IQ scores ranged from 40 to 84(M = 50.23, SD= 11.73). Their PPVT-3 standard scores ranged from 40 to88 (M = 54.66, SD= 18.74). The participants obtained the following stan-dard scores on the WRAT-3: Reading scores ranged from 45 to 84 (M =51.73, SD= 11.37); Spelling scores ranged from 45 to 78 (M = 52.73,




SD= 11.77); and Arithmetic scores ranged from 45 to 67 (M = 49.93, SD=7.7). The sample’s CVLT raw scores ranged from 0 to 41 (M = 15.56, SD=10.11). These descriptive measures reflect a restricted sample range associ-ated with the participants’ level of developmental disability.

Correlations between the K-BIT, PPVT-3, WRAT-3, and CVLT arepresented in Table I. With one exception, all correlations were significant atthe .01 level. Correlations between the K-BIT, PPVT-3, and WRAT-3 werestrong, ranging from .72 to .98. Correlations between the CVLT and theother three measures were moderate, ranging from .45 to .69.

DISCUSSION

In comparing the four tests that comprised this screening battery, therelationships between the K-BIT, PPVT-3, and WRAT-3 were direct, strong,and significant at the .01 level. The strongest correlation was between theK-BIT Vocabulary and the K-BIT Composite, which supports the conceptthat vocabulary is the strongest predictor of overall cognitive ability (Sattler,1992). The correlation between the K-BIT Composite and the PPVT-3 wasstrong, supporting the convergent validity of these two instruments, whichis consistent with previous research (Childers et al., 1994).

Correlations between the K-BIT and WRAT-3 were higher than thosereported by Kaufman and Kaufman (1990b), which provides evidence oftheir convergent validity. The correlations between the PPVT-3 and WRAT-3were higher than those reported by Smith et al. (1991), which support theconvergent validity of these two tests. Further, the Spelling and Reading sub-tests of the WRAT-3 correlated strongly, supporting the direct relationshipof these two academic domains (Sattler, 1992).

The CVLT’s moderate correlations with the other three measures sup-port Boone et al.’s contention that verbal memory is a relatively separateentity when compared to other cognitive processes (Boone et. al., 1998).This is noteworthy, given the verbal nature of these tasks and supports thediscriminant validity of the CVLT as a distinct cognitive measure.

Another implication of this study concerns the development of normsfor the instruments included in this study for individuals with severe deficits.For example, on the K-BIT, 25- to 44-year-old individuals who obtain rawscores of 40 or below receive a standard score of 40. This suggests the K-BITfails to make meaningful discriminations between individuals with low levelsof cognitive functioning. Development of norms for the measures includedin this study for individuals in the severe and profound ranges of mental re-tardation could aid practitioners who assess individuals with developmentaldisabilities.




Tabl

eI.

Cor

rela

tion

sof

the

K-B

IT,P

PV

T-3,

WR

AT-

3,an

dC

VLT

From

aPo

pula

tion

ofA

dult

sW

ith

Dev

elop

men

talD

isab

iliti

es

K-B

ITK

-BIT

K-B

ITW

RA

T-3

WR

AT-

3W

RA

T-3

Voc

abul

ary

Mat

rice

sC

ompo

site

PP

VT-

3R

eadi

ngSp

ellin

gA

rthm

etic

CV

LT

K-B

ITV

ocab

ular

y1.

00K

-BIT

Mat

rice

s.8

4∗1.

00K

-BIT

Com

posi

te.9

8∗.9

3∗1.

00P

PV

T-3

.90∗

.86∗

.92∗

1.00

WR

AT-

3R

eadi

ng.8

1∗.8

5∗.8

6∗.8

1∗1.

00W

RA

T-3

Spel

ling

.76∗

.80∗

.80∗

.72∗

.95∗

1.00

WR

AT-

3A

rith

met

ic.8

4∗.8

7∗.8

8∗.8

6∗.9

1∗.8

5∗1.

00C

VLT

.68∗

.57∗

.67∗

.69∗

.48∗

.45

.55∗

1.00

∗ p<.0

1.




Weaknesses of this study include the representativeness of the sample,which may limit the generalizability of the results. Only participants whoseguardians granted consent and who assented to participate in study were in-cluded. However, participants ranged from 18 to 49 years of age and includedindividuals from borderline intellectual ability to profound levels of mentalretardation. Because of the range of participant age, cognitive functioninglevel, and residence (i.e., all live in a state-operated facility), the sample maybe representative of adults with developmental disabilities residing in an in-termediate care facility/mental retardation. Based upon the current results,future studies evaluating the clinical applicability of this screening batteryappear warranted.

ACKNOWLEDGMENTS

The authors express appreciation to Drs Lynn Bogart, Audrey Courtney,Tom Korn, and Ken Maguire for their support of this project. We also thankKim Wilkins for proofreading this manuscript.

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