Journal of Consulting and Clinical Psychology 1977, Vol. 45, No. S, 808-814
Comparison of the Neuropsychological Key and Discriminant Analysis Approaches in Predicting Cerebral Damage and Localization Dennis P. Swiercinsky
Julia K. Warnock
Veterans Administration Hospital Topeka, Kansas
University of Kansas
The neuropsychological key approach is compared with a stepwise discriminate analysis in terms of accurate "hit" rates for predicting brain damage versus non brain damage and for predicting no brain damage, and left, right, and diffuse brain damage. Additionally, each of these methods of actuarial prediction is discussed with regard to the relative occurrence of false positives and false negatives in the classification matrix. The independent variables include those from the Halstead-Reitan Battery and from the Wechsler Adult Intelligence Scale. Several approaches to statistical or actuarial interpretation of neuropsychological test results have been developed. One relatively popular approach is the neuropsychological key (Russell, Neuringer, & Goldstein, 1970), which is patterned after the biological key species classification technique. The 1970 version predicts diagnoses of brain damage versus no brain damage; right, left, or diffuse lateralization; and static, acute, or congenital process. Swiercinsky and Hallenbeck (1975) and Swiercinsky (1976) described an initial attempt to use factor scores in a multiple regression technique to predict complex test behavior, lateralization, and process in brainimpaired persons. In other studies, attempts have been made to predict diagnostic criteria based on discriminant function analyses of test scores (e.g., Goldstein & Shelly, 1972; Wheeler, Burke, & Reitan, 1963). Other actuarial approaches have variously tried to optimize prediction of brain damage from psychological tests through computerized analyses (Wheeler, 1964; Adams, Rennick, & Rosenbaum, Note 1). The use of factor and discriminant function
analyses have proven valuable in understanding the nature of neuropsychological assessment. Since the key (Russell et al., 1970) has been relatively popular in many clinical neuropsychological settings, an examination of its efficacy of prediction in comparison with other actuarial techniques is appropriate. The present study compares the key with a discriminant function analysis using the same predictive criteria that were originally developed for the key. Goldstein and Shelly (1972) reported correct classification of brain damage versus no brain damage and lateralization by the discriminant analysis in the 60% to 70% range. Russell et al. (1970) reported correct classification for various diagnostic criteria in the 50% to 80% range using the key approach. One problem in comparing these results is that a parallel set of variables was not used in the two studies. However, there was some overlap in the subject population in these two studies. The utility of comparison lies not only in examining overall percents of correct classification but in examining relative occurrence of false positives and false negatives in the classification matrix. An advantage of discriminant function analysis when a stepwise solution is used is that This study was supported by Veterans Administration Research Grant, Topeka Veterans Administration the technique provides an optimal linear comProject 519. bination of the minimal numbers of variables Requests for reprints should be sent to Dennis necessary to classify individuals. Classification Swiercinsky, Topeka Veterans Administration Hospital, formulas may then be derived using the most Topeka, Kansas 66622. 808
PREDICTING CEREBRAL DAMAGE
809
Table 1 Independent Variable Sets Used in the Discriminant Analyses
Independent variable Perceptual disorder score (total) Tactile suppressions Right Left Auditory suppressions Right Left Visual suppressions Right Left Finger agnosia errors Right Left Fingertip writing errors Right Left Tactile dysfunction rating Right Left Auditory dysfunction rating Right Left Seashore rhythm errors Halstead category errors Halstead-Wepman Aphasia screening errors Modified Spatial Relations score Spatial Relations CrossRating score
Key variables
Key variables
For For BD/ lateralizaNBD» tion b
For For BD/ lateralizaNBD" tionb
X X X
X X
X X
X X
X X
X X
X X
X X
X X
X X X X X X
X X X
X
X
X
Independent variable Speech Sounds Perception errors Finger Tapping Dominant speed Nondominant speed Tactual Performance Test (TPT) Total time Right time Left time Memory score Location score Trials B time Trials A time WAIS Verbal IQ Similarities Digit span Vocabulary Information Comprehension Arithmetic Performance IQ Block design Object assembly Picture completion Picture Arrangement Digit Symbol Full Scale IQ Chronological age Years of education
Note. Data Set 3 consists of all independent variables. BD WAIS = Wechsler Adult Intelligence Scale.
economical set of variables to obtain classification prediction. Method Subjects Two hundred sixty patient records with complete data were available from the neuropsychology data pool at the Topeka (Kansas) Veterans Administration Hospital. These patient records had full documentation of unquestioned brain damage, location, and process of damage based on a complete neurological examination. The data pool contains almost exclusively records of male patients with diagnoses (in decreasing order of frequency) of alcoholism, cerebral trauma, cerebrovascular disorder, epilepsy, brain malformation, neoplasm,
X X
X X
X X X X X X
X X X
X X X X
X X
brain damage; NBD = non brain damage;
degenerative disease, toxic poisoning, and infectious disorder. Of the 260 patients, 182 were diagnosed as brain damaged. Among these, 17 were identified as having clearly denned right hemisphere lesions; 22, left; and the remaining, diffuse. These records came from the same pool of case records as used in the Goldstein and Shelly (1972), Swiercinsky and Hallenbeck (1975), and Swiercinsky (1976) studies.
Independent Variables All variables are from the modified Halstead-Reitan Neuropsychological Test Battery, which is normally administered at the Topeka Veterans Administration Hospital (Swiercinsky, Note 2). Scoring and rating details as used in the neuropsychological key are described in Russell et al. (1970).
810
DENNIS P. SWIERCINSKY AND JULIA K. WARNOCK
Three sets of independent variables were used. These are indicated in Table 1. The first set consists of raw scores used in the neuropsychological key to predict the presence or absence of brain damage. Twelve variables are averaged by the key to obtain the average impairment rating. If the average impairment rating is greater than or equal to 1.5S, a prediction of "brain damaged" is made. Nine of the ratings are based directly on nine raw score test variables: Halstead Category, Tactual Performance Test (TPT) Total Time score, TFT Memory, TPT Location, Seashore Rhythm Test, Finger Tapping for dominant hand, Trail Making Test B (Speed), Speech Sounds Perception, and the Revised Halstead-Wepman Aphasia Screening Test. For the other three ratings, conditional comparisons are made among several variables. The Digit Symbol rating is dependent on a comparison of the standard score with a generated variable consisting of Digit Symbol, Picture Arrangement, Picture Completion, and Block Design. The Spatial Relations rating is based on the crosses drawn during the Aphasia Screening Examination, except that the score is increased by 2 points if several relational comparisons among the Wechsler subscales are met. The rating for Perceptual Disorder is based on the sum of tactile, auditory, and visual double simultaneous suppressions and Finger Agnosia and Fingertip Writing errors. (These scoring formulas are described in Russell et al., 1970.) The second set of variables consists of those scores used by the neuropsychological key to determine whether or not there is a lateralized or diffuse lesion. This analysis is made by the key only if the average impairment rating is in the brain-damaged range. The third set of variables consists of a maximum set of scores combining those of Sets 1 and 2, adding the remaining Wechsler Adult Intelligence Scale subtests and adding age and years of education.
Dependent Variables Two sets of dependent variables (groupings) were used for the discriminant function analyses. The first consisted only of two groups: brain damaged and non brain damaged. The second set of groupings consisted of non-brain-damaged, left hemisphere lesion, right hemisphere lesion, and diffuse lesion patients. In all cases only those patient records were used that had a high degree of diagnostic confidence. Cases with questionable diagnoses were omitted from the study. These groupings were made on the basis of the neurologist's final report. The report is based on a physical neurological examination, and, where appropriate, on electroencephalographic, echoencephalographic, pneumoencephalographic, and arteriographic studies. All neurological evaluations were conducted by a staff neurologist or by a resident physician at the Topeka Veterans Administration Hospital.
Procedure Phase 1 consisted of a stepwise linear discriminant function analysis using Independent Variable Set 1 to
predict the presence or absence of brain damage. This analysis provides the linear combination of original predictor variables that have indicated large differences between brain-damaged and non-brain-damaged patients. The percentage of overall classification and positive and negative hits was compared to the percentages based on the neuropsychological key. A second discriminant function analysis was performed using the maximum set of variables (Set 3) against the same grouping criteria. Phase 2 consisted of a stepwise multiple linear discriminant function analysis using Independent Variable Set 2 to predict the grouping of no brain damage, left lesion, right lesion, and diffuse lesion. The percentage of hits obtained with this method is compared to the percentage of correct key predictions of these groups. A similar discriminant function was performed using the maximum set of variables (Set 3).
Statistical Treatment The discriminant function analyses were performed at the University of Kansas using the Honeywell 635 computer. The discriminant analysis program used was from the Statistical Package for the Social Sciences (Nie, Hull, Jenkins, Steinbrenner, & Bent, 1975). For all analyses, Wilks's method of stepwise variable selection was used. Variables are selected in order of largest overall multivariate F value. The minimum F-to-enter value of 1.0 (p assumed .5) was used in all analyses.
Results Table 2 presents the results of the stepwise discriminant analysis for predicting brain damage versus no brain damage. Nine of the Table 2 Results of Discriminant Analysis for Brain-Damaged and Non-Brain-Damaged Groups Utilizing Only "Key" Variables
Step
1 2 3 4 5 6 7 8 9
Variable added to previous variables WAIS Digit Symbol TPT Total Time Auditory Suppressions— Left TPT Memory Test Halstead-Wepman Aphasia Screening Fingertip Writing WAIS Object Assembly Halstead Category Test Seashore Rhythm Test
F
Approximate df
40.21 25.07
1, 258 2, 257
17.78 14.02
3, 256 4, 255
11.59 9.91 8.68
5, 6, 7, 8, 9,
7.77 7.04
254 253 252 251 250
Note. TPT = Tactual Performance Test; WAIS = Wechsler Adult Intelligence Scale.
PREDICTING CEREBRAL DAMAGE Table 3 Results of the Discriminant Analysis]or Brain-Damaged and Non-Brain-Damaged Groups Utilizing the Maximum Set of Variables
Step
Variable added to previous variables
Approximate F
df
1 WAIS Digit Symbol 40.21 2 TPT Left Time 27.51 3 Auditory Suppressions— Left 19.57 4 WAIS Vocabulary 15.54 5 WAIS Information 14.34 6 Years of education 12.68 7 WAIS Similarities 11.35
8 Tactile Dysfunction Hand and Face— Right 9 TPT Memory Test 10 WAIS Object Assembly 11 Fingertip Writing— Right 12 Fingertip Writing— Left
1, 258 2, 257 3, 4, 5, 6, 7,
256 255 254 253 252
10.28 9.S3 8.72
8, 251 9, 250 10, 249
8.03
11, 248
7.53
12, 247
Note. WAIS = Wechsler Adult Intelligence Scale; TPT = Tactual Performance Test. 25 variables contributed meaningful information in maximizing the centroid difference between the two groups. Table 3 presents the results of the same discriminant analysis when the maximum set of variables is used. The final classification prediction matrices are presented in Table 4.
811
In Phase 2, the discriminant analysis is compared with the neuropsychological key in not only making a prediction of brain damage but going beyond to predict lateralization of lesion. Table 5 presents the results of the discriminant analysis using the same variables that the neuropsychological key uses for predicting lateralization. Table 6 presents the same analysis using a maximum set of independent variables. Comparison of the analyses is summarized in Table 7. Discussion The aim of this study was to compare two actuarial methods of neuropsychological prediction. The neuropsychological key approach (Russell et al., 1970) was compared to a multiple discriminant function analysis in terms of accuracy of predicting brain damage and lateralization. The criterion for effectiveness was percentage of correct classification. The results do not support one approach as being more accurate in all situations than the other. In Phase 1, the neuropsychological key was more accurate than the discriminant analysis in predicting brain damage, with 86.8% correct classification as compared to 68.7% in the discriminant approach. However, the key only predicted correctly 48.7% of the non-braindamaged patients, as compared to 71.8% with
Table 4 Classification Predictions for Brain-Damaged Versus Non-Brain-Damaged Subjects Correctly identified
Incorrectly identified
Technique
Brain damaged
Non brain damaged
Brain damaged
Non brain damaged
Total % correctly identified
Neuropsychological keys
158 (86.8)
38 (48.7)
24 (13.2)
40 (51.3)
75.4
Key variables in a discriminant function analysis
125 (68.7)
56 (71.8)
57 (31.3)
22 (28.2)
69.6"
Maximum set of variables in a discriminant function analysis
134 (73.6)
55 (70.5)
48 (26.4)
23 (29.5)
72.7b
Note. Numbers in parentheses are percentages. Based on neurological tests, n for brain-damaged subjects = 182, n for non-brain-damaged subjects = 78. " Nine variables used out of 25. b Twelve variables used out of 44.
812
DENNIS P. SWIERCINSKY AND JULIA K. WARNOCK
Table 5
Results of Discriminant Analysis for Left, Right, Diffuse, and N on-Brain-Damaged Groups Utilizing only "Key" Variables
Step
Variable added to previous variables
F
Approximate df
1 TPT Left Time 12 .66 3, 256 2 Finger Tapping Dominant Average Speed 9.90 6, 510 3 Finger Tapping Nondominant Average Speed 9 .30 9, 618 4 Halstead-Wepman Aphasia Screening 7,,94 12, 669 S Tactile Dysfunction Hands and Face Right 6..84 15, 696 6 Auditory Suppressions— Left 5.94 18, 710 7 WAIS Vocabulary 5..31 21, 718 8 WAIS Digit Span 4.88 24, 722 9 Finger Writing— Right 4 .51 27, 725 10 Visual Suppressions— Right 4..23 30, 725 11 Tactile Dysfunction Hand 3,,95 33, 72b and Face— Left 12 Finger Agnosia— Right 3..74 36, 724
Note. TPT = Tactual Performance Test; WAIS = Wechsler Adult Intelligence Scale.
the discriminant. This finding has implication for diagnosis and rehabilitation. The neuropsychological key approach resulted in 51.3% false positives, whereas the discriminant function yielded only 28.2%. In terms of actual harm to a patient, neither the prospect of being diagnosed as brain damaged when one is not nor the failure to attain a proper diagnosis so that treatment can begin is a desirable alternative. For example, the label brain damaged may have destructive implication for the mentally ill, as Goffman (1963), Scheff (1967), and others have claimed. An individual who has been diagnosed as mildly brain damaged and for whom there is no treatment now merely has another "label" to contend with or has an excuse for his or her behavior (e.g., the former alcoholic with mild impairment in the higher mental processes). On the other hand, it is much more of a serious disservice for an individual to be diagnosed as non brain damaged when he/she does in fact have cerebral impairment for which a proper diagnosis is imperative
for proper treatment (e.g., surgery for a neoplasm, medication to control seizures, recommendation for rehabilitation programs for particular cerebral losses, etc.). In Phase 2, it is interesting to note that the discriminant analysis was more accurate in terms of "hit rates" again for the non-braindamaged (48.7% vs. 66.7%) and for the left, hemisphere-damaged group (27.3% vs. 45.5%). The two approaches are essentially the same in the classification of right hemisphere damage and diffuse damage. It is possible that these particular variables when used with different types of populations will require different approaches to diagnosis. For example, the discriminant function accurately predicted left hemisphere damage better than the key. Table 6 Results of the Discriminant Analysis for Left, Right, Diffuse, and Non-BrainDamaged Groups Utilizing the Maximum Set of Variables
Step
Variable added to previous variable
1 WAIS Digit Symbol 2 Finger Tapping Dominant
Average Speed
F
Approximate df
13.71
3, 256
9.55
6, 510
9.09 8.16 7.33
9, 618 12, 669 IS, 696
6.59 6.11 5.74 5.38 5.09
18, 21, 24, 27, 30,
710 718 722 725 726
4.84 4.64 4.40 4.19 4.00 3.66 3.53 3.44
33, 36, 39, 42, 45, 51, 54, ,57,
725 724 723 721 719 715 712 710
3.35 3.36
60, 707 60, 707
3 Finger Tapping Non4
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
dominant Average Speed TPT Left Time Trail Making A Time Tactile Dysfunction Hand and Face— Right Years education Speech Sounds Perception WAIS Vocabulary TPT Memory Score Auditory Suppression— Left WAIS Picture Completion WAIS Information WAIS Digit Span Halstead Category Test Spatial Relation Crosses Finger Agnosia— Left Finger Agnosia— Right Tactile Dysfunction Hand and Face— Left Seashore Rhythm Test Halstead Wepman Aphasia Screening
3.25 63, 705
Note. WAIS = Wechsler Adult Intelligence Scale; TPT = Tactual Performance Test.
PREDICTING CEREBRAL DAMAGE
813
Table 7 Classification Predictions for Non Brain Damage, Left Hemisphere, and Right Hemisphere Versus Diffuse Brain Damage Brain damage Actual diagnosis
Non brain damage
Left
Right
Diffuse
Using the neuropsychological keys" Non brain damage Brain damage Left Right Diffuse
38 (48.7)
11 (14.1)
7 ( 8.9)
22 (28.2)
3 (13.6) 4 (23.5) 17 (11.9)
6 (27.3) 2 (11.7) 30 (20.9)
7 (31.8) 6 (35.3) 35 (24.5)
6 (27.3) 5 (29.4) 61 (42.7)
Using key variables in discriminant function11 Non brain damage Brain damage Left Right Diffuse
52 (66.7)
6 ( 7.7)
7 ( 9.0)
13 (16.7)
7 (31.8) 5 (29.4) 29 (20.3)
10 (45.5) 1 ( 5.9) 19 (13.3)
1 ( 4.5) 6 (35.3) 28 (19.6)
4 (18.2) 5 (29.4) 67 (46.9)
Using a maximum battery set of variables in discriminant function 0 Non brain damage Brain damage Left Right Diffuse
51 (65.4)
4 ( 5.1)
8 (10.3)
15 (19.2)
4 (18.2) 5 (29.4) 34 (23.8)
14 (63.6) 0 13 ( 9.1)
1 ( 4.5) 9 (52.9) 22 (15.4)
3 (13.6) 3 (17.6) 74 (51.7)
Note. Numbers in parentheses are percentages. Based on neurological tests, n for non-brain-damaged subjects = 78, left hemisphere damage n = 22, right hemisphere damage n = 17, diffuse brain damage n = 143. "42.7% of cases correctly identified. b 51.9% of cases correctly identified (12 variables used out of 25). c 56.9% of cases correctly identified (21 variables used out of 44).
It is suggested that in certain circumstances, both the discriminant and the key could be used by the neuropsychologist to aid in diagnosis. It is imperative that the neuropsychologist be aware of the data base in which he or she is involved, so that actuarial improvements in terms of hit rates can be made. Thus, if within a particular neuropsychology setting the discriminant function is more accurate than the key in number of hit rates for a particular subgroup (e.g., left hemisphere damage), then the psychologist can also weigh this additional bit of information accordingly in terms of making a diagnosis. When the maximum set of variables is included, additional information could be examined for improving predictions. The aim is to consider other variables that discriminate well between the groups that may not be included among the key variables.
Comparing Tables 2 and 3, it can be seen that about half of the variables overlap between the two analyses. However, very little improvement is seen in overall classification (69.6% vs. 72.7%). The discriminant function using a maximum set of variables can predict about as consistently as the key while requiring only 12 variables instead of the 25 required by the key. Comparison of the two discriminants in the prediction of left, right, or diffuse damage, and non brain damage yields more encouraging results supporting a discriminant approach. Approximately half of the variables again overlap. Requiring only 12 of the 25 variables used by the key, discriminant function was able to improve overall classification by about 10%. Improvement was another 5% when 22 variables of the 44 in the maximum set were used.
814
DENNIS P. SWIERCINSKY AND JULIA K. WARNOCK
The discriminant function approach to classifying patients appears to have a promising future. Not only is classification better than using the key, but it is considerably more economical. Classification formulas need to be derived and used on subsequent patients to examine the stability of such formulas. Reference Notes 1. Adams, K. M., Rennick, P. M., & Rosenbaum, G. Automated clinical interpretation of the neuropsychology battery. Paper presented at the meeting of the International Ncuropsychology Society, Tampa, Florida, February 6, 1975. 2. Swiercinsky, D. Manual for adult neuropsychology testing and evaluation. Topcka, Kans.: Veterans Administration Hospital, 1975.
References Goffman, I. Stigma: Notes on the management of spoiled identity. Englewood Cliffs, N. J.: Prentice-Hall, 1963. Goldstein, G., & Shelly, C. 11. Statistical and normative studies of the Halstead-Reitan neuropsychological
test battery relevant to a neuropsychiatric setting. Perceptual and Motor Skills, 1972, 34, 603-620. Nie, N. H., Hull, C. H., Jenkins, J. G., Steinbrenner, K., & Bent, D. H. Statistical package for the social sciences (2nd ed.). New York: McGraw-Hill, 1975. Russell, E. W., Neuringer, C., & Goldstein, G. Assessment of brain damage—A neuropsychological key approach. New York: Wilcy-Interscience, 1970. Scheff, T. J. (Ed.) Mental illness and social processes. New York: Harper & Row, 1967. Swiercinsky, D. Prediction of specific brain damage location and process of the neuropsychological factor approach. Journal of Clinical Psychology, 1976, 32, 651-654. Swiercinsky, D., & Hallenbeck, C. E. A factorial approach to neuropsychological assessment. Journal of Clinical Psychology, 1975, 31, 610-618. Wheeler, L. Complex behavioral indices weighted by linear discriminant functions for the prediction of cerebral damage. Perceptual and Motor Skills, 1964, 19, 907-923. Wheeler, L., Burke, C. J., & Reitan, R. M. An application of discriminant functions to the problem of predicting brain damage using behavioral variables. Perceptual and Motor Skills, 1963, 16, 417-440.
Received June 14, 1976 •
Comparison of the Neuropsychological Key and Discriminant Analysis Approaches in Predicting Cerebral Damage and Localization Dennis P. Swiercinsky
Julia K. Warnock
Veterans Administration Hospital Topeka, Kansas
University of Kansas
The neuropsychological key approach is compared with a stepwise discriminate analysis in terms of accurate "hit" rates for predicting brain damage versus non brain damage and for predicting no brain damage, and left, right, and diffuse brain damage. Additionally, each of these methods of actuarial prediction is discussed with regard to the relative occurrence of false positives and false negatives in the classification matrix. The independent variables include those from the Halstead-Reitan Battery and from the Wechsler Adult Intelligence Scale. Several approaches to statistical or actuarial interpretation of neuropsychological test results have been developed. One relatively popular approach is the neuropsychological key (Russell, Neuringer, & Goldstein, 1970), which is patterned after the biological key species classification technique. The 1970 version predicts diagnoses of brain damage versus no brain damage; right, left, or diffuse lateralization; and static, acute, or congenital process. Swiercinsky and Hallenbeck (1975) and Swiercinsky (1976) described an initial attempt to use factor scores in a multiple regression technique to predict complex test behavior, lateralization, and process in brainimpaired persons. In other studies, attempts have been made to predict diagnostic criteria based on discriminant function analyses of test scores (e.g., Goldstein & Shelly, 1972; Wheeler, Burke, & Reitan, 1963). Other actuarial approaches have variously tried to optimize prediction of brain damage from psychological tests through computerized analyses (Wheeler, 1964; Adams, Rennick, & Rosenbaum, Note 1). The use of factor and discriminant function
analyses have proven valuable in understanding the nature of neuropsychological assessment. Since the key (Russell et al., 1970) has been relatively popular in many clinical neuropsychological settings, an examination of its efficacy of prediction in comparison with other actuarial techniques is appropriate. The present study compares the key with a discriminant function analysis using the same predictive criteria that were originally developed for the key. Goldstein and Shelly (1972) reported correct classification of brain damage versus no brain damage and lateralization by the discriminant analysis in the 60% to 70% range. Russell et al. (1970) reported correct classification for various diagnostic criteria in the 50% to 80% range using the key approach. One problem in comparing these results is that a parallel set of variables was not used in the two studies. However, there was some overlap in the subject population in these two studies. The utility of comparison lies not only in examining overall percents of correct classification but in examining relative occurrence of false positives and false negatives in the classification matrix. An advantage of discriminant function analysis when a stepwise solution is used is that This study was supported by Veterans Administration Research Grant, Topeka Veterans Administration the technique provides an optimal linear comProject 519. bination of the minimal numbers of variables Requests for reprints should be sent to Dennis necessary to classify individuals. Classification Swiercinsky, Topeka Veterans Administration Hospital, formulas may then be derived using the most Topeka, Kansas 66622. 808
PREDICTING CEREBRAL DAMAGE
809
Table 1 Independent Variable Sets Used in the Discriminant Analyses
Independent variable Perceptual disorder score (total) Tactile suppressions Right Left Auditory suppressions Right Left Visual suppressions Right Left Finger agnosia errors Right Left Fingertip writing errors Right Left Tactile dysfunction rating Right Left Auditory dysfunction rating Right Left Seashore rhythm errors Halstead category errors Halstead-Wepman Aphasia screening errors Modified Spatial Relations score Spatial Relations CrossRating score
Key variables
Key variables
For For BD/ lateralizaNBD» tion b
For For BD/ lateralizaNBD" tionb
X X X
X X
X X
X X
X X
X X
X X
X X
X X
X X X X X X
X X X
X
X
X
Independent variable Speech Sounds Perception errors Finger Tapping Dominant speed Nondominant speed Tactual Performance Test (TPT) Total time Right time Left time Memory score Location score Trials B time Trials A time WAIS Verbal IQ Similarities Digit span Vocabulary Information Comprehension Arithmetic Performance IQ Block design Object assembly Picture completion Picture Arrangement Digit Symbol Full Scale IQ Chronological age Years of education
Note. Data Set 3 consists of all independent variables. BD WAIS = Wechsler Adult Intelligence Scale.
economical set of variables to obtain classification prediction. Method Subjects Two hundred sixty patient records with complete data were available from the neuropsychology data pool at the Topeka (Kansas) Veterans Administration Hospital. These patient records had full documentation of unquestioned brain damage, location, and process of damage based on a complete neurological examination. The data pool contains almost exclusively records of male patients with diagnoses (in decreasing order of frequency) of alcoholism, cerebral trauma, cerebrovascular disorder, epilepsy, brain malformation, neoplasm,
X X
X X
X X X X X X
X X X
X X X X
X X
brain damage; NBD = non brain damage;
degenerative disease, toxic poisoning, and infectious disorder. Of the 260 patients, 182 were diagnosed as brain damaged. Among these, 17 were identified as having clearly denned right hemisphere lesions; 22, left; and the remaining, diffuse. These records came from the same pool of case records as used in the Goldstein and Shelly (1972), Swiercinsky and Hallenbeck (1975), and Swiercinsky (1976) studies.
Independent Variables All variables are from the modified Halstead-Reitan Neuropsychological Test Battery, which is normally administered at the Topeka Veterans Administration Hospital (Swiercinsky, Note 2). Scoring and rating details as used in the neuropsychological key are described in Russell et al. (1970).
810
DENNIS P. SWIERCINSKY AND JULIA K. WARNOCK
Three sets of independent variables were used. These are indicated in Table 1. The first set consists of raw scores used in the neuropsychological key to predict the presence or absence of brain damage. Twelve variables are averaged by the key to obtain the average impairment rating. If the average impairment rating is greater than or equal to 1.5S, a prediction of "brain damaged" is made. Nine of the ratings are based directly on nine raw score test variables: Halstead Category, Tactual Performance Test (TPT) Total Time score, TFT Memory, TPT Location, Seashore Rhythm Test, Finger Tapping for dominant hand, Trail Making Test B (Speed), Speech Sounds Perception, and the Revised Halstead-Wepman Aphasia Screening Test. For the other three ratings, conditional comparisons are made among several variables. The Digit Symbol rating is dependent on a comparison of the standard score with a generated variable consisting of Digit Symbol, Picture Arrangement, Picture Completion, and Block Design. The Spatial Relations rating is based on the crosses drawn during the Aphasia Screening Examination, except that the score is increased by 2 points if several relational comparisons among the Wechsler subscales are met. The rating for Perceptual Disorder is based on the sum of tactile, auditory, and visual double simultaneous suppressions and Finger Agnosia and Fingertip Writing errors. (These scoring formulas are described in Russell et al., 1970.) The second set of variables consists of those scores used by the neuropsychological key to determine whether or not there is a lateralized or diffuse lesion. This analysis is made by the key only if the average impairment rating is in the brain-damaged range. The third set of variables consists of a maximum set of scores combining those of Sets 1 and 2, adding the remaining Wechsler Adult Intelligence Scale subtests and adding age and years of education.
Dependent Variables Two sets of dependent variables (groupings) were used for the discriminant function analyses. The first consisted only of two groups: brain damaged and non brain damaged. The second set of groupings consisted of non-brain-damaged, left hemisphere lesion, right hemisphere lesion, and diffuse lesion patients. In all cases only those patient records were used that had a high degree of diagnostic confidence. Cases with questionable diagnoses were omitted from the study. These groupings were made on the basis of the neurologist's final report. The report is based on a physical neurological examination, and, where appropriate, on electroencephalographic, echoencephalographic, pneumoencephalographic, and arteriographic studies. All neurological evaluations were conducted by a staff neurologist or by a resident physician at the Topeka Veterans Administration Hospital.
Procedure Phase 1 consisted of a stepwise linear discriminant function analysis using Independent Variable Set 1 to
predict the presence or absence of brain damage. This analysis provides the linear combination of original predictor variables that have indicated large differences between brain-damaged and non-brain-damaged patients. The percentage of overall classification and positive and negative hits was compared to the percentages based on the neuropsychological key. A second discriminant function analysis was performed using the maximum set of variables (Set 3) against the same grouping criteria. Phase 2 consisted of a stepwise multiple linear discriminant function analysis using Independent Variable Set 2 to predict the grouping of no brain damage, left lesion, right lesion, and diffuse lesion. The percentage of hits obtained with this method is compared to the percentage of correct key predictions of these groups. A similar discriminant function was performed using the maximum set of variables (Set 3).
Statistical Treatment The discriminant function analyses were performed at the University of Kansas using the Honeywell 635 computer. The discriminant analysis program used was from the Statistical Package for the Social Sciences (Nie, Hull, Jenkins, Steinbrenner, & Bent, 1975). For all analyses, Wilks's method of stepwise variable selection was used. Variables are selected in order of largest overall multivariate F value. The minimum F-to-enter value of 1.0 (p assumed .5) was used in all analyses.
Results Table 2 presents the results of the stepwise discriminant analysis for predicting brain damage versus no brain damage. Nine of the Table 2 Results of Discriminant Analysis for Brain-Damaged and Non-Brain-Damaged Groups Utilizing Only "Key" Variables
Step
1 2 3 4 5 6 7 8 9
Variable added to previous variables WAIS Digit Symbol TPT Total Time Auditory Suppressions— Left TPT Memory Test Halstead-Wepman Aphasia Screening Fingertip Writing WAIS Object Assembly Halstead Category Test Seashore Rhythm Test
F
Approximate df
40.21 25.07
1, 258 2, 257
17.78 14.02
3, 256 4, 255
11.59 9.91 8.68
5, 6, 7, 8, 9,
7.77 7.04
254 253 252 251 250
Note. TPT = Tactual Performance Test; WAIS = Wechsler Adult Intelligence Scale.
PREDICTING CEREBRAL DAMAGE Table 3 Results of the Discriminant Analysis]or Brain-Damaged and Non-Brain-Damaged Groups Utilizing the Maximum Set of Variables
Step
Variable added to previous variables
Approximate F
df
1 WAIS Digit Symbol 40.21 2 TPT Left Time 27.51 3 Auditory Suppressions— Left 19.57 4 WAIS Vocabulary 15.54 5 WAIS Information 14.34 6 Years of education 12.68 7 WAIS Similarities 11.35
8 Tactile Dysfunction Hand and Face— Right 9 TPT Memory Test 10 WAIS Object Assembly 11 Fingertip Writing— Right 12 Fingertip Writing— Left
1, 258 2, 257 3, 4, 5, 6, 7,
256 255 254 253 252
10.28 9.S3 8.72
8, 251 9, 250 10, 249
8.03
11, 248
7.53
12, 247
Note. WAIS = Wechsler Adult Intelligence Scale; TPT = Tactual Performance Test. 25 variables contributed meaningful information in maximizing the centroid difference between the two groups. Table 3 presents the results of the same discriminant analysis when the maximum set of variables is used. The final classification prediction matrices are presented in Table 4.
811
In Phase 2, the discriminant analysis is compared with the neuropsychological key in not only making a prediction of brain damage but going beyond to predict lateralization of lesion. Table 5 presents the results of the discriminant analysis using the same variables that the neuropsychological key uses for predicting lateralization. Table 6 presents the same analysis using a maximum set of independent variables. Comparison of the analyses is summarized in Table 7. Discussion The aim of this study was to compare two actuarial methods of neuropsychological prediction. The neuropsychological key approach (Russell et al., 1970) was compared to a multiple discriminant function analysis in terms of accuracy of predicting brain damage and lateralization. The criterion for effectiveness was percentage of correct classification. The results do not support one approach as being more accurate in all situations than the other. In Phase 1, the neuropsychological key was more accurate than the discriminant analysis in predicting brain damage, with 86.8% correct classification as compared to 68.7% in the discriminant approach. However, the key only predicted correctly 48.7% of the non-braindamaged patients, as compared to 71.8% with
Table 4 Classification Predictions for Brain-Damaged Versus Non-Brain-Damaged Subjects Correctly identified
Incorrectly identified
Technique
Brain damaged
Non brain damaged
Brain damaged
Non brain damaged
Total % correctly identified
Neuropsychological keys
158 (86.8)
38 (48.7)
24 (13.2)
40 (51.3)
75.4
Key variables in a discriminant function analysis
125 (68.7)
56 (71.8)
57 (31.3)
22 (28.2)
69.6"
Maximum set of variables in a discriminant function analysis
134 (73.6)
55 (70.5)
48 (26.4)
23 (29.5)
72.7b
Note. Numbers in parentheses are percentages. Based on neurological tests, n for brain-damaged subjects = 182, n for non-brain-damaged subjects = 78. " Nine variables used out of 25. b Twelve variables used out of 44.
812
DENNIS P. SWIERCINSKY AND JULIA K. WARNOCK
Table 5
Results of Discriminant Analysis for Left, Right, Diffuse, and N on-Brain-Damaged Groups Utilizing only "Key" Variables
Step
Variable added to previous variables
F
Approximate df
1 TPT Left Time 12 .66 3, 256 2 Finger Tapping Dominant Average Speed 9.90 6, 510 3 Finger Tapping Nondominant Average Speed 9 .30 9, 618 4 Halstead-Wepman Aphasia Screening 7,,94 12, 669 S Tactile Dysfunction Hands and Face Right 6..84 15, 696 6 Auditory Suppressions— Left 5.94 18, 710 7 WAIS Vocabulary 5..31 21, 718 8 WAIS Digit Span 4.88 24, 722 9 Finger Writing— Right 4 .51 27, 725 10 Visual Suppressions— Right 4..23 30, 725 11 Tactile Dysfunction Hand 3,,95 33, 72b and Face— Left 12 Finger Agnosia— Right 3..74 36, 724
Note. TPT = Tactual Performance Test; WAIS = Wechsler Adult Intelligence Scale.
the discriminant. This finding has implication for diagnosis and rehabilitation. The neuropsychological key approach resulted in 51.3% false positives, whereas the discriminant function yielded only 28.2%. In terms of actual harm to a patient, neither the prospect of being diagnosed as brain damaged when one is not nor the failure to attain a proper diagnosis so that treatment can begin is a desirable alternative. For example, the label brain damaged may have destructive implication for the mentally ill, as Goffman (1963), Scheff (1967), and others have claimed. An individual who has been diagnosed as mildly brain damaged and for whom there is no treatment now merely has another "label" to contend with or has an excuse for his or her behavior (e.g., the former alcoholic with mild impairment in the higher mental processes). On the other hand, it is much more of a serious disservice for an individual to be diagnosed as non brain damaged when he/she does in fact have cerebral impairment for which a proper diagnosis is imperative
for proper treatment (e.g., surgery for a neoplasm, medication to control seizures, recommendation for rehabilitation programs for particular cerebral losses, etc.). In Phase 2, it is interesting to note that the discriminant analysis was more accurate in terms of "hit rates" again for the non-braindamaged (48.7% vs. 66.7%) and for the left, hemisphere-damaged group (27.3% vs. 45.5%). The two approaches are essentially the same in the classification of right hemisphere damage and diffuse damage. It is possible that these particular variables when used with different types of populations will require different approaches to diagnosis. For example, the discriminant function accurately predicted left hemisphere damage better than the key. Table 6 Results of the Discriminant Analysis for Left, Right, Diffuse, and Non-BrainDamaged Groups Utilizing the Maximum Set of Variables
Step
Variable added to previous variable
1 WAIS Digit Symbol 2 Finger Tapping Dominant
Average Speed
F
Approximate df
13.71
3, 256
9.55
6, 510
9.09 8.16 7.33
9, 618 12, 669 IS, 696
6.59 6.11 5.74 5.38 5.09
18, 21, 24, 27, 30,
710 718 722 725 726
4.84 4.64 4.40 4.19 4.00 3.66 3.53 3.44
33, 36, 39, 42, 45, 51, 54, ,57,
725 724 723 721 719 715 712 710
3.35 3.36
60, 707 60, 707
3 Finger Tapping Non4
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
dominant Average Speed TPT Left Time Trail Making A Time Tactile Dysfunction Hand and Face— Right Years education Speech Sounds Perception WAIS Vocabulary TPT Memory Score Auditory Suppression— Left WAIS Picture Completion WAIS Information WAIS Digit Span Halstead Category Test Spatial Relation Crosses Finger Agnosia— Left Finger Agnosia— Right Tactile Dysfunction Hand and Face— Left Seashore Rhythm Test Halstead Wepman Aphasia Screening
3.25 63, 705
Note. WAIS = Wechsler Adult Intelligence Scale; TPT = Tactual Performance Test.
PREDICTING CEREBRAL DAMAGE
813
Table 7 Classification Predictions for Non Brain Damage, Left Hemisphere, and Right Hemisphere Versus Diffuse Brain Damage Brain damage Actual diagnosis
Non brain damage
Left
Right
Diffuse
Using the neuropsychological keys" Non brain damage Brain damage Left Right Diffuse
38 (48.7)
11 (14.1)
7 ( 8.9)
22 (28.2)
3 (13.6) 4 (23.5) 17 (11.9)
6 (27.3) 2 (11.7) 30 (20.9)
7 (31.8) 6 (35.3) 35 (24.5)
6 (27.3) 5 (29.4) 61 (42.7)
Using key variables in discriminant function11 Non brain damage Brain damage Left Right Diffuse
52 (66.7)
6 ( 7.7)
7 ( 9.0)
13 (16.7)
7 (31.8) 5 (29.4) 29 (20.3)
10 (45.5) 1 ( 5.9) 19 (13.3)
1 ( 4.5) 6 (35.3) 28 (19.6)
4 (18.2) 5 (29.4) 67 (46.9)
Using a maximum battery set of variables in discriminant function 0 Non brain damage Brain damage Left Right Diffuse
51 (65.4)
4 ( 5.1)
8 (10.3)
15 (19.2)
4 (18.2) 5 (29.4) 34 (23.8)
14 (63.6) 0 13 ( 9.1)
1 ( 4.5) 9 (52.9) 22 (15.4)
3 (13.6) 3 (17.6) 74 (51.7)
Note. Numbers in parentheses are percentages. Based on neurological tests, n for non-brain-damaged subjects = 78, left hemisphere damage n = 22, right hemisphere damage n = 17, diffuse brain damage n = 143. "42.7% of cases correctly identified. b 51.9% of cases correctly identified (12 variables used out of 25). c 56.9% of cases correctly identified (21 variables used out of 44).
It is suggested that in certain circumstances, both the discriminant and the key could be used by the neuropsychologist to aid in diagnosis. It is imperative that the neuropsychologist be aware of the data base in which he or she is involved, so that actuarial improvements in terms of hit rates can be made. Thus, if within a particular neuropsychology setting the discriminant function is more accurate than the key in number of hit rates for a particular subgroup (e.g., left hemisphere damage), then the psychologist can also weigh this additional bit of information accordingly in terms of making a diagnosis. When the maximum set of variables is included, additional information could be examined for improving predictions. The aim is to consider other variables that discriminate well between the groups that may not be included among the key variables.
Comparing Tables 2 and 3, it can be seen that about half of the variables overlap between the two analyses. However, very little improvement is seen in overall classification (69.6% vs. 72.7%). The discriminant function using a maximum set of variables can predict about as consistently as the key while requiring only 12 variables instead of the 25 required by the key. Comparison of the two discriminants in the prediction of left, right, or diffuse damage, and non brain damage yields more encouraging results supporting a discriminant approach. Approximately half of the variables again overlap. Requiring only 12 of the 25 variables used by the key, discriminant function was able to improve overall classification by about 10%. Improvement was another 5% when 22 variables of the 44 in the maximum set were used.
814
DENNIS P. SWIERCINSKY AND JULIA K. WARNOCK
The discriminant function approach to classifying patients appears to have a promising future. Not only is classification better than using the key, but it is considerably more economical. Classification formulas need to be derived and used on subsequent patients to examine the stability of such formulas. Reference Notes 1. Adams, K. M., Rennick, P. M., & Rosenbaum, G. Automated clinical interpretation of the neuropsychology battery. Paper presented at the meeting of the International Ncuropsychology Society, Tampa, Florida, February 6, 1975. 2. Swiercinsky, D. Manual for adult neuropsychology testing and evaluation. Topcka, Kans.: Veterans Administration Hospital, 1975.
References Goffman, I. Stigma: Notes on the management of spoiled identity. Englewood Cliffs, N. J.: Prentice-Hall, 1963. Goldstein, G., & Shelly, C. 11. Statistical and normative studies of the Halstead-Reitan neuropsychological
test battery relevant to a neuropsychiatric setting. Perceptual and Motor Skills, 1972, 34, 603-620. Nie, N. H., Hull, C. H., Jenkins, J. G., Steinbrenner, K., & Bent, D. H. Statistical package for the social sciences (2nd ed.). New York: McGraw-Hill, 1975. Russell, E. W., Neuringer, C., & Goldstein, G. Assessment of brain damage—A neuropsychological key approach. New York: Wilcy-Interscience, 1970. Scheff, T. J. (Ed.) Mental illness and social processes. New York: Harper & Row, 1967. Swiercinsky, D. Prediction of specific brain damage location and process of the neuropsychological factor approach. Journal of Clinical Psychology, 1976, 32, 651-654. Swiercinsky, D., & Hallenbeck, C. E. A factorial approach to neuropsychological assessment. Journal of Clinical Psychology, 1975, 31, 610-618. Wheeler, L. Complex behavioral indices weighted by linear discriminant functions for the prediction of cerebral damage. Perceptual and Motor Skills, 1964, 19, 907-923. Wheeler, L., Burke, C. J., & Reitan, R. M. An application of discriminant functions to the problem of predicting brain damage using behavioral variables. Perceptual and Motor Skills, 1963, 16, 417-440.
Received June 14, 1976 •
