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Discrepancies between the California Verbal Learning Test: Children's version and the Children's Category Test after pediatric traumatic brain injury
Published online by Cambridge University Press: 01 July 2005
Abstract
One hundred 9–16-year-old children with traumatic brain injury (TBI) completed the California Verbal Learning Test–Children's Version (CVLT–C) and the Children's Category Test (CCT) within 1 year after injury. Performance contrasts between these two instruments that were unusually large (> 16 T score points) were about as common in this clinical sample as in the standardization sample of both instruments. However, relatively poor performance on the CVLT–C as compared to the CCT was associated with prolonged coma and lower scores on the Processing Speed index of the Wechsler Intelligence Scale for Children–Third Edition. It is concluded that a relative weakness on the CVLT–C is more likely to reflect cerebral compromise after pediatric TBI than is a relative weakness on the CCT. (JINS, 2005, 11, 386–391.)
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- Research Article
- Information
- Journal of the International Neuropsychological Society , Volume 11 , Issue 4 , July 2005 , pp. 386 - 391
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- © 2005 The International Neuropsychological Society
INTRODUCTION
Traumatic brain injury (TBI) is a common condition where cerebral compromise is incurred as the direct or indirect result of an acute external force to the skull. Children with TBI often do well on tests of routinized or overlearned skills whereas they tend to have significant difficulties with learning of, and problem solving with, novel or complex information (for reviews see Donders & Kuldanek, 1998; Yeates, 2000). The introduction of the California Verbal Learning Test–Children's Version (CVLT–C; Delis et al., 1994) and the Children's Category Test (CCT; Boll, 1993) in the mid-1990s provided the opportunity for contrasting measures of, respectively, verbal learning and problem solving with visual materials. These two instruments were standardized and normed on the same sample and also offered reliable age-corrected standard scores, which allowed for direct comparisons of respective performances. The purpose of the current investigation was to determine the frequency of occurrence of unusually large discrepancies between the results from both tests in a large sample of children with TBI, and to determine if the direction of such discrepancies was meaningfully related to injury variables.
There has been considerable research demonstrating the criterion validity of the CVLT–C when applied to children with TBI. This test is sensitive to severity of injury (Levin et al., 2000; Roman et al., 1998), is strongly predictive of educational outcome two years postinjury (Miller & Donders, 2003), and shows only partial recovery at even more extended follow-up (Yeates et al., 2002). There is less extensive research with the CCT but there is some evidence that it too is affected by severity of pediatric TBI (Hoffman et al., 2000). To our knowledge, no previous study has explored specifically performance discrepancies between the CVLT–C and the CCT in clinical samples. This is regrettable because clinicians are prone to underestimate the base rates of differences in test scores (Schinka et al., 1998). Research with the standardization sample of these instruments has suggested that seemingly large and statistically significant discrepancies between the respective T scores of these two instruments are fairly common (Donders, 1998). In that study, it was recommended on the basis of base rate analyses that in children between the ages of 9 and 16 years, only discrepancies greater than 16 T-score points should be interpreted in clinical practice. Specifically, CVLT–C T scores that exceeded the CCT T score by 17 or more points occurred in only 9.83% of the standardization sample, whereas 10.67% of that same sample had a discrepancy of that magnitude in the opposite direction. In the current exploratory investigation, we planned to investigate how often such unusually large discrepancies occurred in children with TBI, and whether the direction of those discrepancies was related to injury characteristics.
Performance contrasts between tests of memory and problem solving like the CVLT–C and CCT are of interest not only for pragmatic or psychometric reasons but also from a theoretical perspective. A number of recent studies have reported impaired performance on other tests of memory (Catroppa & Anderson, 2002; Lowther & Mayfield, 2004) or problem solving (Mangeot et al., 2002; Slomine et al., 2002) after pediatric TBI but rarely have the reasons for doing well or poorly in one domain versus the other been explored. A recent factor analysis study found that measures of memory and problem solving loaded on different latent constructs (Brookshire et al., 2004). Many tests of memory, including the CVLT–C, make significant demands on speed of information processing, which is often affected after pediatric TBI (Catroppa & Anderson, 2003; Donders & Warschausky, 1997), whereas many tests of problem solving like the CCT are not only free of time constraints but also provide frequent feedback. It has been suggested that the extensive supports built into many of these kinds of problem-solving tasks may actually help the child compensate for any executive impairment that he/she has, thereby limiting ecological validity of the instruments (Silver, 2000). For all of these reasons, an investigation of the frequency and correlates of unusually large discrepancies between the CVLT–C and the CCT in a clinical sample of children with TBI appeared to be warranted.
METHOD
Research Participants
The 100 participants for this investigation were selected from a consecutive series of original referrals to a regional Midwestern rehabilitation hospital. Patient selection continued for approximately 7½ years until there were 100 children who met all of the following criteria: (1) diagnosis of TBI, defined as an external blunt force to the head with associated alteration of consciousness; (2) age between 9 and 16 years at the time of psychometric assessment; (3) absence of a premorbid neurological, psychiatric, personal abuse, or special education history (as ascertained from both parent report and review of medical and academic records); and (4) assessment with the CVLT–C and CCT within 1 year after injury. Over the time period that these data were collected, these two tests were administered routinely to all referred children at the organization where this study was completed, except in cases where there were confounding factors (e.g., non-English language background, severe uncorrected visual impairment) that could have invalidated the child's performance. The relative influences of demographic and neurological variables on performance on, respectively, the CVLT–C and CCT in this sample have been described in a separate investigation (Donders & Nesbit-Greene, 2004). Performance contrasts between the two instruments were not addressed in that study.
The final sample included 57 boys and 43 girls. Ethnicities, based on parent designation, included Caucasian (n = 78), Latino (n = 10), African-American (n = 6), and Asian-American (n = 6). Parental occupations were coded according to the primary wage earner in the household and included professional (n = 19), clerical (n = 28), skilled labor (n = 40), and unskilled labor or homemaker (n = 13). On average, children were seen for neuropsychological assessment at 83.00 days after injury (SD = 60.79, Median = 61.50, range = 14–330), at an age of 14.15 years (SD = 2.32, Median = 14.69, range = 9.00–16.75). Most of the participants had been injured in motor vehicle collisions, as passengers (n = 45), pedestrians (n = 15), cyclists (n = 7), or drivers (n = 10). Other injury circumstances included falls (n = 11), recreational accidents (n = 8), and other (n = 4). Injury severity was defined on the basis of length of coma (i.e., time until there was a meaningful response to verbal commands) and results from neuroimaging of the brain in acute care. Children with mild TBI (n = 35) had length of coma < 24 hr and no evidence for an acute intracranial lesion on computed tomography (CT) or magnetic resonance imaging (MRI) scan. Children with moderate-severe TBI (n = 65) had either coma of at least 24 hr (n = 32) or evidence for an intracranial lesion on neuroimaging (n = 63) or both. In the latter group, mean length of coma was 2.90 days (SD = 5.18, Median = 0.50, range = 0–25).
Materials
The CVLT–C is an individually administered test of a child's ability to learn and remember a shopping list containing five items from each of three semantic categories. Although numerous indexes can be obtained from the CVLT–C, the main variable of interest for the current investigation was the summary T score (M = 50, SD = 10), reflecting a global index of immediate free recall over successive trials, with higher scores reflecting better performance. In the complete sample, the mean composite T score on the CVLT–C was 47.18 (SD = 12.82, Median = 50.00, range 20–70) and 21% had results in the impaired range, defined as scores at or below the 10th percentile (T ≤ 37).
The CCT is an individually administered test of a child's ability to solve problems on the basis of corrective feedback (“right”/“wrong”) about each attempt at identifying the conceptual rule underlying visually presented test items. The total number of errors on this task can be converted into a T score (M = 50, SD = 10), with higher scores reflecting better performance. In the complete sample, the mean composite T score on the CCT was 46.81 (SD = 9.75, Median = 47.00, range 22–70) and 17% scored at or below the 10th percentile (T ≤ 37).
Procedure
The CVLT–C and CCT were administered in a standardized manner as part of neuropsychological evaluations that were requested in the context of rehabilitation, most often (84%) on an outpatient basis. The CCT was administered routinely during the interval between the short-delay cued recall and long-delay free recall trials of the CVLT–C. Evaluations were performed only when the children were medically stable and could recall meaningful information from day to day. A performance contrast was calculated by subtracting the CCT T score from the CVLT–C T score.
RESULTS
In the complete sample, the median difference between the CVLT–C and CCT T scores was .50 points, with a range from −44 to 33. There were 11 children who had a CVLT–C T score that was more than 16 points lower than their CCT T score (High CCT group), and also 11 children who had a discrepancy of that magnitude in the opposite direction (High CVLT–C group). Figure 1 presents the respective performances of these two groups. It should be realized the term “High” is used here only to reflect relative performance on one test as compared to the other, and not to indicate any classification based on age-based norms.
Performance of children with unusually large contrasts on the California Verbal Learning Test–Children's Version (CVLT–C) and Children's Category Test (CCT).
There were no statistically significant differences between the High CCT and High CVLT–C groups in terms of ethnicity (dichotomized as Caucasian vs. Other), parental occupational status (dichotomized as professional or clerical vs. skilled or unskilled/homemaker), age, or time since injury (p > .10 for all variables). However, the High CCT group was composed exclusively of boys whereas only 4/11 children in the High CVLT–C group were boys, Fisher's Exact Test p < .01. In addition, only 1 child in the High CVLT–C group had a duration of coma of 1 day (with all others having coma < 30 min) whereas length of coma equaled or exceeded 24 hr in 7/11 children in the High CCT group, Fisher's Exact Test p < .05, Odds Ratio = 17.50 (90% confidence interval = 2.35–130.57).
In order to determine if the apparent disparity in distribution of coma among the High CVLT–C and High CCT groups reflected a more general difference between the two tests in sensitivity to injury severity, Spearman correlations were calculated between the T scores from the respective tests and length of coma in the complete sample (n = 100). The correlation with length of coma was greater for the CVLT–C (r = −.53, p < .0001) than for the CCT (r = −.28, p < .01). This difference was statistically significant, t = 2.46, p < .05. We also compared the groups with moderate-severe (n = 65) and mild (n = 35) TBI on these two psychometric variables. There was a relatively more robust contrast in favor of the mild TBI group on the CVLT–C, F(1,98) = 11.06, p < .001, η2 = .10, than on the CCT, F(1,98) = 4.47, p < .05, η2 = .04, but this difference fell short of statistical significance, z = 1.50, p < .10.
Results from the Wechsler Intelligence Scale for Children–Third Edition (WISC–III; Wechsler, 1991) were also available for all participants in the two contrast groups. These findings are presented in Figure 2. A multivariate analysis of variance with groups (n = 2) as the independent variable and WISC–III factor index scores (n = 4) as the dependent variables yielded a statistically significant main effect, F(4,17) = 3.15, p < .05. Post hoc analyses indicated that this was accounted for exclusively by Processing Speed, with the High CCT group performing worse than the High CVLT–C group, F(1,21) = 12.74, p < .01. This was associated with a large univariate effect size, η2 = 38.91.
Performance of children with unusually large contrasts on the Wechsler Intelligence Scale for Children–Third Edition. CVLT–C = California Verbal Learning Test–Children's Version. CCT = Children's Category Test. VC = Verbal Comprehension. PO = Perceptual Organization. FD = Freedom from Distractibility. PS = Processing Speed.
Finally, we wanted to determine which factors affected the magnitude of the discrepancy between the CVLT–C and the CCT in the complete sample because an exclusive focus on two groups at the extreme ends of a spectrum can sometimes be misleading. For this reason, we performed a multiple regression analysis with the discrepancy score as the dependent variable and the following independent variables, entered as a single block: gender, parental occupational status, ethnicity, presence or absence of an intracranial lesion on neuroimaging, length of coma, time since injury, and the four WISC–III factor index scores. Because of the restricted age range of this sample and the fact that both CVLT–C and CCT T scores are age-corrected, we did not include age at assessment in this analysis. The resulting findings are presented in Table 1. Consistent with previous recommendations (Harrell, 2001; Millis, 2003), it was decided a priori to leave both statistically significant and nonsignificant variables in the model in order to allow the reader to determine independently the relative contribution of all variables in concert.
Regression model for discrepancy score between CVLT–C and CCT in 100 children with traumatic brain injury
The regression model for the discrepancy between the CVLT–C and the CCT was statistically significant, F(10,89) = 3.20, p < .01, adjusted R2 = .18, and multicollinearity diagnostics were unremarkable. Inspection of Table 1 suggests that larger positive discrepancies between the two instruments (i.e., CVLT–C T score being higher than the CCT T score) were associated with female gender, shorter length of coma, and better performance on the WISC–III Verbal Comprehension index. None of the other variables were statistically significant predictors of the discrepancy score.
DISCUSSION
The frequencies of unusually large (> 16 points) discrepancies between the T scores from, respectively, the CVLT–C and the CCT in this investigation were almost identical to those reported previously for the standardization sample (Donders, 1998). Thus, pediatric TBI is not associated with an atypical rate of discrepancies between indexes of learning and problem solving, as assessed by these instruments. However, the direction of the discrepancy was meaningfully related to external criterion variables. Children who did relatively poorly on the CVLT–C as compared to the CCT were all boys and were much more likely to have been in coma for at least 24 hr.
The current findings suggest that relatively poor performance on the CVLT–C was more likely to be reflective of cerebral compromise (as reflected in length of coma) than relatively poor performance on the CCT. The former pattern was also associated with poor performance on WISC–III Processing Speed, a variable that was strongly correlated with length of coma (r = −.63, p < .0001). The gender differences between the two contrasting groups are consistent with the fact that a female advantage on the CVLT–C has also been described in the standardization sample (Kramer et al., 1997). In a previous study with the current participants, it was demonstrated that coma and gender explained incremental (i.e., additive) variance in performance on the CVLT–C in the complete sample, with no evidence for a moderating effect and no evidence for a gender effect on the CCT (Donders & Nesbit-Greene, 2004).
In the complete sample, performance on the WISC–III Verbal Comprehension index also contributed to prediction of the discrepancy between the CVLT–C and the CCT, above and beyond the effects of gender and length of coma. Verbal Comprehension is a variable that was largely unaffected by severity of TBI, as reflected in its very low correlation with length of coma (r = .09, p > .10). These findings suggest that the general magnitude of the performance contrast between the CVLT–C and the CCT after pediatric TBI is related to both premorbid verbal ability level and injury severity. However, premorbid verbal strengths do not appear to play much of a role in the emergence of performance contrasts that are, by base rate standards, unusually large.
The findings from this investigation are limited by the utilization of a referred convenience sample and the relatively small sizes of the contrasting groups. However, a broad range of injury severities was represented and the participants had been screened carefully for possible confounding factors. In order to have data from the same test with all children, we also limited this investigation to the older children's version (9–16 years) of the CCT and replication with the younger children's version (5–8 years; Boll, 1993) is still needed. Although most children in this sample had also received other tests of memory and problem solving, these tended to differ with the age of the children and over the course of the 7½ years of this study, so we were unable to compare systematically the groups with large performance discrepancies on such other tests.
With these reservations in mind, the results are consistent with a broader literature supporting the criterion validity of the CVLT–C with regard to pediatric TBI (Levin et al., 2000; Roman et al., 1998; Yeates et al., 2002) whereas selective impairment on the CCT may not necessarily be reflective of acquired deficits. This finding cannot be explained by differences in ranges of scores because these spanned about 5 standard deviations for both instruments in this sample. Part of the problem with the CCT may be that the component subtests differ considerably in sensitivity to injury severity, with subtest III being especially problematic, which may distort the composite T score (Nesbit-Greene & Donders, 2002). The CCT also provides a considerable degree of structure and redirection to the child, which is a problem with many purported tests of executive functioning (Silver, 2000), whereas the format of the CVLT–C puts the burden squarely on the examinee to organize the information in the most efficient manner. Another factor may be that the CCT does not make any demands on speed of performance whereas the CVLT–C involves presentation of stimuli at a fairly rapid rate, and speed of information processing is commonly impaired after pediatric TBI (Donders & Warschausky, 1997; Tremont et al., 1999). In fact, there is evidence that speed of information processing may mediate the effect of injury severity on performance on the CVLT–C (Donders & Nesbit-Greene, 2004).
The fact that the CVLT–C and CCT were standardized and age-normed on the same large, representative, national sample had potential appeal because of the allowance for direct comparisons between the composite indexes from both instruments. However, these two tests do not have equivalent sensitivity to severity of TBI, with criterion validity being much more convincing for the CVLT–C. Exclusive reliance on the CCT as a measure of novel problem solving in neuropsychological evaluations of children with TBI may be ill-advised and supplementation with other measures that also include a speed component (e.g., Tower of London; Shum & Griffith, 2000) might be considered. A goal for future research is the exploration of performance contrasts between the CVLT–C and CCT in other clinical samples.
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Performance of children with unusually large contrasts on the California Verbal Learning Test–Children's Version (CVLT–C) and Children's Category Test (CCT).
Performance of children with unusually large contrasts on the Wechsler Intelligence Scale for Children–Third Edition. CVLT–C = California Verbal Learning Test–Children's Version. CCT = Children's Category Test. VC = Verbal Comprehension. PO = Perceptual Organization. FD = Freedom from Distractibility. PS = Processing Speed.
Regression model for discrepancy score between CVLT–C and CCT in 100 children with traumatic brain injury
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