Abstract

The performance of 54 patients with complicated mild–severe traumatic brain injury (TBI) was evaluated on the Attention, Executive Functions, and Memory modules of the Neuropsychological Assessment Battery (NAB) and compared with that of 54 demographically matched healthy controls. All three NAB indices demonstrated statistically significant group differences and negative covariances with the duration of coma, with large effect sizes. The Numbers and Letters and Mazes subtests had the most consistent evidence for sensitivity to brain injury. The findings provide preliminary support for the criterion validity of the NAB in the assessment of patients with complicated mild–severe TBI.

Introduction

Traumatic brain injury (TBI) is a common acquired neurological condition that affects more than 800,000 adults per year in the USA. TBI can be defined as an acute, external force to the head, with associated alteration of consciousness. Especially when it is complicated by prolonged coma and/or intracranial abnormalities on neuroimaging, it often results in cognitive impairments (for comprehensive reviews, see Hanks, Ricker, & Millis, 2004; Roebuck-Spencer, Baños, Sherer, & Novack, 2010). Among these, deficits in attention, memory, and executive functioning are particularly common and persistent (Anderson & Knight, 2010; DeJong & Donders, 2010; Draper & Ponsford, 2008). This investigation examined the performance of adults with TBI on a comprehensive assessment instrument, the Neuropsychological Assessment Battery (NAB; Stern & White, 2003).

The NAB is a battery of various tests, intended for use with adult patients, that assesses five cognitive domains: Attention, Language, Memory, Spatial, and Executive Functions. Since all the tasks were based on a single sample, using the method of continuous norming, the NAB has the distinct advantage of allowing direct comparison of a patient's performance across various domains. In addition, the norms take into account not only age but also level of education, which allows for more realistic interpretations of the data in light of the patient's premorbid history. Reliabilities for the various domain scores are good, ranging from 0.79 to 0.93 in the standardization sample. However, studies of applications of the NAB in clinical samples have been somewhat limited to date. There has been some support for specific NAB tasks in samples ranging from dementia (Gavett et al., 2009) to stroke (Stricker, Tybur, Sadek, & Haaland, 2010) to substance abuse (Grohman & Fals-Stewart, 2004). However, only one prior study has examined the performance of patients with TBI on the NAB. Zgaljardic and Temple (2010) found that the screening module of the NAB appeared to measure some of the same constructs as more conventional neuropsychological tests in a sample of patient with various forms of acquired brain injury who had been admitted to a post-acute residential rehabilitation program. However, no published study has investigated the criterion validity of the NAB in greater detail. Information of this kind is important in light of the fact that psychometric tests should be validated for the specific clinical populations with which they are used (American Educational Research Association, American Psychological Association, & National Council on Measurement in Education, 1999).

The purpose of the current investigation was to investigate the sensitivity of NAB Attention, Executive Function, and Memory scales to TBI, because those domains are most often affected by that condition. Consistent with some of the criteria used in previous research with other instruments (e.g., Strong & Donders, 2008; Strong, Tiesma, & Donders, 2011), it was decided a priori that, in order for the NAB to be clinically useful, (a) the mean performances of patients with TBI should be statistically significantly worse than those of demographically matched, neurologically healthy controls; (b) within the TBI group, NAB indexes should demonstrate statistically significant negative correlations with the length of coma; and (c) effect sizes should be at least in the moderate range (i.e., η2 ≥ 0.10 for group comparisons, and r2 ≥ 0.10 for correlations).

Methods

Participants

After receiving institutional review board approval, archival data were retrieved from a consecutive series of referred patients with TBI who were evaluated through the private practice of the second author over a period of 6 years. The 54 clinical participants met the following criteria: (1) ≥18 years and ≤70 years of age, (2) diagnosis of TBI with evidence for an acute intracranial lesion on neuroimaging; (3) neuropsychological assessment with inclusion of the NAB Attention, Executive Functions, and Memory modules, (4) no prior history of pervasive developmental disorder, progressive neurological disease, or psychosis, and (5) scoring in the valid range on an independent measure of effort and motivation; i.e., the Word Memory Test (Green, 2003). During the time period that these data were collected, these three NAB modules had been administered routinely to all adult patients with TBI who were referred for neuropsychological evaluation at the practice where this investigation was pursued, except in cases where there were complicating circumstances that would have invalidated the test results (e.g., English not being the primary language or severe uncorrected visual impairment). Only results from initial evaluations were considered.

The final clinical sample was comprised of 37 men (69%) and 17 women (31%), with a mean age of 29.96 years (SD = 13.41) and a mean level of education of 11.61 years (SD = 2.11). The majority of patients in the sample were Caucasian (n = 44; 81%), with the remainder being Aboriginal (n = 10, 19%). The vast majority (n = 51; 94%) of these participants sustained their injuries as the result of a motor vehicle accident, with the remainder including falls and assaults. The median time since injury was 11 months (M = 18.76, SD = 17.47, range 3–81). Persons with prior histories of outpatient treatment for either substance abuse (n = 10, 19%) or non-psychotic emotional adjustment problems (n = 5, 9%) or both (n = 3, 6%) were not excluded from this investigation because it was planned to investigate the impact of such comorbidities on NAB performance. However, persons with prior significant medical/neurological histories (e.g., meningitis, epilepsy) were excluded, consistent with procedures used for the NAB standardization sample (Stern & White, 2003). There was active disputed financial compensation-seeking pending in three cases (6%).

Since an inclusion criterion for this study was that there had to be neuroimaging evidence for an intracranial lesion, there were no persons with uncomplicated mild TBI in the final sample. Eleven patients (20%) required emergent craniotomy, most often because of diffuse edema and/or significant midline shift associated with epidural hematoma. Other intracranial findings ranged from focal hemorrhagic contusions to diffuse axonal injury. The lowest post-resuscitation Glasgow Coma Scale (GCS) scores ranged from 3 to 15, with a median of 7. There were 40 patients (74%) with GCS scores in the severe range (3–8), 7 (13%) with GCS scores in the moderate range (9–12), and 7 patients with GCS scores in the mild range (13–15). The median duration of coma, defined as the number of days until there was a reliable response to verbal commands, was 2.5 days (M = 7.09, SD = 9.29, range = 0–31 days). More than half of the sample (n = 32, 59%) had coma ≥24 h, whereas about a quarter of the sample (n = 15, 28%) had coma ≤30 min.

A comparison group of 54 persons from the standardization sample was subsequently requested from the publisher of the NAB. These control participants were closely matched to clinical patients on the basis of age, gender, ethnicity (dichotomized as Caucasian vs. others) and level of education. Post hoc comparisons of the two groups confirmed that there were no meaningful differences between them on any of these demographic variables (all p's > .50).

Measures

Three modules from the NAB were included in this investigation. Only measures for which interval-level normative scores were available were included in the analyses. All NAB subtests yield age-, education-, and gender-corrected T scores (M = 50, SD = 10), with higher scores reflecting better performance. Domain-specific subtest T scores can also be combined into, respectively, Attention, Executive Functions, and Memory indices, expressed as standard scores (M = 100, SD = 15), with higher scores again reflecting better performance.

Procedure

The NAB was administered to clinical patients in a standardized manner, on an outpatient basis, when they were medically stable and could recall meaningful information from day to day. Hierarchical linear regression was used to determine to what extent performance on any of the NAB index scores could be predicted by demographic background variables (i.e., age, gender, ethnicity, education, prior substance abuse history, prior psychiatric history, compensation-seeking status, and time since injury). Since none of those variables were statistically significant predictors of performance on any of the three NAB indices, they were not included as covariates in any further analyses. Group mean differences on the NAB index scores were evaluated with a multivariate analysis of variance. Within the TBI group, the Spearman correlations were used to determine the relationship between the duration of coma and the NAB variables.

Results

The performance of the two groups on the NAB index scores is presented in Table 1. A multivariate analysis of variance with groups (n = 2) as the independent variable and the three NAB index scores as the dependent variables yielded a statistically significant main effect of groups, F (3, 104) = 14.16, p < .0001, with the patients with TBI performing worse than the demographically matched controls. The group differences were statistically significant for all NAB indices, with effect sizes in the large range for Attention and Memory and in the moderate range for Executive Functions. All indexes demonstrated statistically significant correlations with the length of coma, with the amount of variance explained ranging from 10% (Memory) to 24% (Executive Functions).

Table 1.

Performance (in standard scores) on the NAB

 Index TBI (n = 54)
 
Control (n = 54)
 
η2 (95% CI) d (95% CI) r with coma r2 
 M SD M SD     
Attention 82.83 16.05 98.21 12.71 0.22 (0.10–0.35) 1.07 (−1.63–3.77) −.43 (p < .002) .19 
Memory 86.61 14.87 101.89 12.55 0.24 (0.11–0.36) 1.12 (−1.46–3.68) −.32 (p < .017) .10 
Executive Functions 92.56 15.47 103.52 12.88 0.13 (0.04–0.25) 0.77 (−1.88–3.44) −.49 (p < .001) .24 
 Index TBI (n = 54)
 
Control (n = 54)
 
η2 (95% CI) d (95% CI) r with coma r2 
 M SD M SD     
Attention 82.83 16.05 98.21 12.71 0.22 (0.10–0.35) 1.07 (−1.63–3.77) −.43 (p < .002) .19 
Memory 86.61 14.87 101.89 12.55 0.24 (0.11–0.36) 1.12 (−1.46–3.68) −.32 (p < .017) .10 
Executive Functions 92.56 15.47 103.52 12.88 0.13 (0.04–0.25) 0.77 (−1.88–3.44) −.49 (p < .001) .24 

Notes: TBI = traumatic brain injury; CI = confidence interval. The control group selected from the standardization data from the Neuropsychological Assessment Battery by R. A. Stern and T. White. © 2003 by Psychological Assessment Resources, Inc. (PAR), Lutz, FL. Used by special permission. All rights reserved. Further reproduction prohibited without permission from PAR, Inc.

Because group averages can obscure relative frequencies of impairment, we also evaluated how often the patients with TBI and the controls obtained NAB index standard scores below 80. This would represent a level of performance below the 10th percentile, a commonly used cut-off for consideration of impairment. Patients with TBI were more than seven times more likely (n = 23, 43%) to have Attention scores <80 than controls (n = 5, 9%), χ2 (n = 108) = 15.62, p < .0001, OR = 7.27 (90% CI = 2.97–17.80). Similarly, these patients were more than eight times more likely (n = 18, 33%) to have Memory scores <80 than controls (n = 3, 6%), χ2 (n = 108) = 13.39, p < .0003, OR = 8.50 (90% CI = 2.87–25.19). Finally, patients with TBI were also more than four times more likely (n = 8, 15%) to have Executive Functions scores <80 than controls (n = 2, 4%), χ2 (n = 108) = 3.97, p < .05, OR = 4.52 (90% CI = 1.18–17.31).

Finally, we performed post hoc analyses of the NAB subtests. We were particularly interested in those subtests that showed both a statistically significant mean difference between the two groups and a statistically significant correlation with the length of coma. To balance the risk of Type I and Type II errors with so many comparisons, α was set at 0.01 and a minimum effect size of 0.10 was maintained. Only Numbers and Letters A, Numbers and Letters C, and Mazes met these criteria (Table 2).

Table 2.

Performance (in T scores) on subtests of the NAB

Subtest TBI (n = 54)
 
Control (n = 54)
 
η2 (95% CI) d (95% CI) R with coma r2 
 M SD M SD     
Digits Forward 43.41 8.07 52.35 8.77 0.23 (0.10–0.35) 1.06 (−0.50–2.65) −.07 (p > .10) .01 
Digits Backward 45.65 8.18 49.98 9.01 0.06 (0.01–0.16) 0.50 (−1.10–2.12) −.01 (p > .10) .00 
Dots 47.17 10.84 49.33 9.95 0.01 (0.00–0.08) 0.21 (−1.73–2.15) −.35 (p < .01) .12 
Numbers and Letters A 36.48 12.95 46.83 8.77 0.18 (0.07–0.31) 0.94 (−1.12–3.01) −.44 (p < .001) .19 
Numbers and Letters B 41.87 9.89 47.98 10.87 0.08 (0.01–0.19) 0.59 (−1.35–2.54) −.53 (p < .0001) .28 
Numbers and Letters C 43.39 7.23 49.72 9.19 0.13 (0.03–0.25) 0.77 (−0.77–2.32) −.33 (p < .02) .11 
Numbers and Letters D 39.78 10.66 48.15 9.89 0.14 (0.04–0.27) 0.81 (−1.11–2.75) −.28 (p < .05) .08 
Driving Scenes 46.83 10.28 50.67 8.51 0.04 (0.00–0.13) 0.41 (−1.35–2.17) −.24 (p < .08) .06 
List Learning A IR 39.46 10.57 52.13 9.02 0.30 (0.16–0.42) 1.29 (−0.53–3.14) −.22 (p > .10) .05 
List Learning B IR 44.91 9.04 50.87 10.23 0.09 (0.01–0.20) 0.62 (−1.18–2.43) −.05 (p > .10) .00 
List Learning A SDR 38.76 12.07 50.93 8.59 0.26 (0.12–0.38) 1.16 (−0.79–3.13) −.07 (p > .10) .01 
List Learning A LDR 39.13 11.93 50.41 8.03 0.24 (0.11–0.36) 1.11 (−0.78–3.02) −.24 (p < .08) .06 
Shape Learning IRC 48.91 10.65 51.82 9.59 0.02 (0.00–0.10) 0.29 (−1.64–2.18) −.52 (p < .0001) .27 
Shape Learning DRC 45.78 11.30 51.41 9.42 0.07 (0.01–0.18) 0.54 (−1.40–2.49) −.39 (p < .004) .15 
Story Learning IR 45.04 9.87 50.83 9.91 0.08 (0.01–0.19) 0.59 (−1.26–2.44) −.19 (p > .10) .04 
Story Learning DR 44.94 9.08 50.00 9.81 0.07 (0.01–0.17) 0.54 (−1.23–2.31) −.32 (p < .02) .10 
Daily Living IR 44.35 8.64 50.07 8.43 0.10 (0.02–0.22) 0.67 (−0.92–2.27) −.19 (p > .10) .04 
Daily Living DR 46.39 12.61 52.78 6.33 0.10 (0.02–0.21) 0.64 (−1.22–2.51) −.07 (p > .10) .01 
Mazes 44.94 11.91 52.94 9.71 0.12 (0.03–0.24) 0.74 (−1.29–2.77) −.57 (p < .0001) .33 
Judgment 49.20 12.05 50.93 9.84 0.01 (0.00–0.07) 0.16 (−1.90–2.21) −.23 (p < .10) .05 
Categories 47.35 10.62 51.93 10.31 0.05 (0.00–0.14) 0.44 (−1.51–2.40) −.52 (p < .0001) .27 
Word Generation 45.39 8.43 51.04 9.90 0.09 (0.01–0.20) 0.62 (−1.10–2.34) −.04 (p > .10) .00 
Subtest TBI (n = 54)
 
Control (n = 54)
 
η2 (95% CI) d (95% CI) R with coma r2 
 M SD M SD     
Digits Forward 43.41 8.07 52.35 8.77 0.23 (0.10–0.35) 1.06 (−0.50–2.65) −.07 (p > .10) .01 
Digits Backward 45.65 8.18 49.98 9.01 0.06 (0.01–0.16) 0.50 (−1.10–2.12) −.01 (p > .10) .00 
Dots 47.17 10.84 49.33 9.95 0.01 (0.00–0.08) 0.21 (−1.73–2.15) −.35 (p < .01) .12 
Numbers and Letters A 36.48 12.95 46.83 8.77 0.18 (0.07–0.31) 0.94 (−1.12–3.01) −.44 (p < .001) .19 
Numbers and Letters B 41.87 9.89 47.98 10.87 0.08 (0.01–0.19) 0.59 (−1.35–2.54) −.53 (p < .0001) .28 
Numbers and Letters C 43.39 7.23 49.72 9.19 0.13 (0.03–0.25) 0.77 (−0.77–2.32) −.33 (p < .02) .11 
Numbers and Letters D 39.78 10.66 48.15 9.89 0.14 (0.04–0.27) 0.81 (−1.11–2.75) −.28 (p < .05) .08 
Driving Scenes 46.83 10.28 50.67 8.51 0.04 (0.00–0.13) 0.41 (−1.35–2.17) −.24 (p < .08) .06 
List Learning A IR 39.46 10.57 52.13 9.02 0.30 (0.16–0.42) 1.29 (−0.53–3.14) −.22 (p > .10) .05 
List Learning B IR 44.91 9.04 50.87 10.23 0.09 (0.01–0.20) 0.62 (−1.18–2.43) −.05 (p > .10) .00 
List Learning A SDR 38.76 12.07 50.93 8.59 0.26 (0.12–0.38) 1.16 (−0.79–3.13) −.07 (p > .10) .01 
List Learning A LDR 39.13 11.93 50.41 8.03 0.24 (0.11–0.36) 1.11 (−0.78–3.02) −.24 (p < .08) .06 
Shape Learning IRC 48.91 10.65 51.82 9.59 0.02 (0.00–0.10) 0.29 (−1.64–2.18) −.52 (p < .0001) .27 
Shape Learning DRC 45.78 11.30 51.41 9.42 0.07 (0.01–0.18) 0.54 (−1.40–2.49) −.39 (p < .004) .15 
Story Learning IR 45.04 9.87 50.83 9.91 0.08 (0.01–0.19) 0.59 (−1.26–2.44) −.19 (p > .10) .04 
Story Learning DR 44.94 9.08 50.00 9.81 0.07 (0.01–0.17) 0.54 (−1.23–2.31) −.32 (p < .02) .10 
Daily Living IR 44.35 8.64 50.07 8.43 0.10 (0.02–0.22) 0.67 (−0.92–2.27) −.19 (p > .10) .04 
Daily Living DR 46.39 12.61 52.78 6.33 0.10 (0.02–0.21) 0.64 (−1.22–2.51) −.07 (p > .10) .01 
Mazes 44.94 11.91 52.94 9.71 0.12 (0.03–0.24) 0.74 (−1.29–2.77) −.57 (p < .0001) .33 
Judgment 49.20 12.05 50.93 9.84 0.01 (0.00–0.07) 0.16 (−1.90–2.21) −.23 (p < .10) .05 
Categories 47.35 10.62 51.93 10.31 0.05 (0.00–0.14) 0.44 (−1.51–2.40) −.52 (p < .0001) .27 
Word Generation 45.39 8.43 51.04 9.90 0.09 (0.01–0.20) 0.62 (−1.10–2.34) −.04 (p > .10) .00 

Notes: TBI = traumatic brain injury; IR = Immediate Recall; DR = Delayed Recall; SDR = Short Delayed Recall; LDR = Long Delayed Recall; IRC = Immediate Recognition; DRC = Delayed Recognition. The control group selected from the standardization data from the Neuropsychological Assessment Battery by R. A. Stern and T. White. © 2003 by Psychological Assessment Resources, Inc. (PAR), Lutz, FL. Used by special permission. All rights reserved. Further reproduction prohibited without permission from PAR.

Discussion

Patients with TBI obtained the mean scores that were statistically significantly lower than those of demographically matched healthy controls on all of the three NAB indices. In addition, all three indices had statistically significant negative correlations with the length of coma. The strong sensitivity of the Numbers and Letters (A and C) and Mazes subtests to TBI in this investigation may be explained at least in part by deficits in speed of information processing, because these tasks are either timed or present stimuli at a fairly rapid pace. Slowness of processing speed is common in patients with TBI (Donders, Tulsky, & Zhu, 2001). Several other studies have reported that a reduction in processing speed was a major factor in lowering the performance of patients with TBI on various cognitive tasks (Ríos, Periáñez, & Muñoz-Céspedes, 2004; Willmott, Ponsford, Hocking, & Schönberger, 2009). A goal for future research is the application of functional neuroimaging to get a better understanding of the regional areas of activation during Numbers and Letters and Mazes in both patients with TBI and neurologically healthy participants.

It should be noted that the a priori criteria for clinical utility in this investigation were fairly stringent, emphasizing not only statistical significance but also two kinds of effect size: one for the proportion of the variance that was accounted for in mean group differences and one for the proportion of a dose–response relationship (i.e., covariance with coma) that could be explained by NAB measures. This decision was made because it would allow identification of those tasks that had the most consistent evidence of criterion validity. There were several NAB subtests that showed some promise but fell short of these conservative criteria. For example, several of the List Learning subtests demonstrated considerable group differences but did not have convincing covariance with the length of coma. The current findings should not be misconstrued as suggesting that such other subtests have no potential clinical utility whatsoever; they just did not meet the high bar that was set a priori for purposes of the current exploratory investigation. Future research should determine the potential sensitivity of such subtests in conditions with circumscribed focal lesions (e.g., left medial temporal involvement in patients with intractable epilepsy).

Some limitations of this study must also be considered. First of all, we used a referred convenience sample of patients with complicated mild–severe TBI. Consequently, these results should not be generalized to mild, uncomplicated TBI, which is typically not associated with persistent cognitive impairment (Iverson, 2005; Schretlen & Shapiro, 2003). Second, we had to rely on radiologists' reports for the neuroimaging data, and we were consequently not able to do volumetric analyses of cerebral lesion volume, or fractional anisotropy based on diffusion tensor data, and the covariance of such variables with NAB performance. Third, we had to dichotomize ethnicity, and further investigation of the validity of the NAB in specific minority groups with neurological impairment is still needed, particularly since the non-Caucasian individuals in our clinical group were Aboriginal, for which there are no equivalent ethnic counterparts in the NAB standardization sample. Fourth, our clinical group consisted of Canadian citizens, whereas the NAB norms are based on a U.S. sample, which may not be completely equivalent in educational attainment and test performance.

It must also be realized that this investigation addressed only the sensitivity of the NAB to TBI; we cannot make statement on the basis of these findings as to whether the NAB subtests actually measure the specific cognitive domains that are purportedly examined with them. Evaluation of construct validity through confirmatory factor analysis, and of concurrent validity through the exploration of correlation with other tests of attention, memory, and executive functioning, is another goal for future research. Such future studies should also included comparisons with clinical but non-TBI (e.g., orthopedic) controls.

With these reservations in mind, we conclude that the findings provide preliminary support for the NAB Attention, Memory, and Executive Function composite indices, as well as the Numbers and Letters and Mazes subtests, as having sufficient criterion validity and potential “added value” in the assessment of complicated mild–severe TBI. Of course, no NAB subtest should ever be used in isolation, or even as the only measure of attention or executive functioning in a neuropsychological assessment. A specific goal for future research is investigation of the utility of NAB tasks to predict longer-term psychosocial outcomes (e.g., community integration or quality of life) after complicated mild–severe TBI.

Funding

There was no source of financial support for this research.

Conflict of Interest

None of the authors have any conflict of interest to declare.

Acknowledgements

The assistance of Jonathan Fugelsang with database management was appreciated. The authors also thank Psychological Assessment Resources, the publisher of the NAB, for allowing access to the standardization sample for control participants (© 2003 by Psychological Assessment Resources, Inc. [PAR], Lutz, FL. Used by special permission. All rights reserved. Further reproduction prohibited without permission from PAR, Inc.).

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