HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): John L. Knight Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Kneebone, A. C. Articles by Knight, J. L. Search for Related Content PubMed PubMed Citation Articles by Kneebone, A. C. Articles by Knight, J. L.

Ann Thorac Surg 1998;65:1320-1325
© 1998 The Society of Thoracic Surgeons

Neuropsychologic Changes After Coronary Artery Bypass Grafting: Use of Reliable Change Indices

^a Department of Health Psychology, Flinders Medical Centre, Adelaide, South Australia, Australia
^b Department of Surgery, Flinders Medical Centre, Adelaide, South Australia, Australia

Accepted for publication December 19, 1997.

Address reprint requests to Dr Baker, Cardiac Surgical Research Group, Department of Surgery, Flinders Medical Centre, Bedford Park, SA 5042 Australia

	Abstract

Top Abstract Introduction Material and methods Results Comment Acknowledgments References

 
Background. A method of defining change in neuropsychologic test scores that accounts for test reliability and practice effects was applied to determine accurately the incidence of acquired neuropsychologic deficits after coronary artery bypass grafting.

Methods. Neuropsychologic assessment was performed on 50 patients before and at 7 days after either hypothermic or normothermic coronary artery bypass grafting. From a matched control group of 24 normal subjects who were examined twice over a similar interval, reliable change indices that controlled for measurement error and practice effects were calculated for each neuropsychologic measure. With the use of these indices, the incidence of postoperative decline among the study patients was determined. For comparison, the incidence of decline using the "one standard deviation" criterion also was calculated.

Results. Comparing the reliable change and standard deviation methods, statistically significant differences in the incidence of decline were observed in 5 of 11 neuropsychologic measures. The reliable change method identified more patients with neuropsychologic deficits on most measures.

Conclusions. The control of measurement error and practice effects can alter significantly the calculated incidence of neuropsychologic impairment after coronary artery bypass grafting.

	Introduction

Top Abstract Introduction Material and methods Results Comment Acknowledgments References

 
Numerous studies have attempted to define the incidence of acquired neuropsychologic dysfunction after cardiac operations that involve the use of cardiopulmonary bypass. The reported incidence of acquired neuropsychologic dysfunction has ranged from 13% to 79% in patients examined before hospital discharge [1, 2] and from 5% to 35% in patients examined 6 to 12 months after operation [3, 4]. Newman [5] ascribed this wide variation in incidence to various cross-study differences in patient selection criteria, technical approaches used in cardiopulmonary bypass, postsurgical follow-up times, and the sensitivity and number of neuropsychologic tests administered.

The variability in the incidence of neuropsychologic impairment also has been shown to depend on the statistical criteria used to infer that meaningful change has occurred. At present, there is no agreement as to what degree of change is indicative of neuropsychologic dysfunction. In a single sample of patients undergoing coronary artery bypass grafting (CABG), Mahanna and colleagues [6] compared the incidence of postoperative neuropsychologic dysfunction with the use of four commonly used criteria of impairment: (1) a decline of 1 standard deviation (SD) from the preoperative test score on 20% of measures, (2) a decline in test scores by at least 20% from baseline on at least 20% of measures, (3) impairment indices adjusted for age, and (4) impairment indices unadjusted for age. Depending on the criteria used, the incidence of postoperative decline ranged from 15% to 66% before hospital discharge and from 3% to 19% at 6 months’ follow-up.

Within the published literature, of more concern than the lack of uniformity in defining neuropsychologic change is the fact that the methods that have been used are based on arbitrary statistical decisions that have no theoretic underpinning. One of the most commonly used approaches to defining postoperative neuropsychologic dysfunction is the SD method, in which a patient is considered to have deteriorated if his or her change score equals or exceeds 1 SD of the group mean preoperative score on that measure. Consistent with the arbitrariness of this approach, there is little agreement as to how the criteria should be applied. Whereas some studies have used the SD method in isolation [2], other studies have used another condition that the decline of 1 SD must occur on two or more tests [7] or on 20% of tests [6].

Despite the lack of a theoretic foundation for the SD criteria of change, and the recommendation of the Statement of Consensus on Assessment of Neurobehavioural Outcomes After Cardiac Surgery [8] that practice effects [9] be considered in any analyses of change data, the SD method is still widely used [10, 11]. However, there is emerging recognition of the importance of defining "real" change in test-retest scores as opposed to "artifactual" change resulting from low test reliability and susceptibility to practice effects [12, 13]. Failure to take into account these factors, as in the arbitrary cutoff methods, has the potential to lead to significant underestimation or overestimation of the incidence of neuropsychologic dysfunction after CABG.

To define more accurately "real" change by controlling for the reliability of a test measure, Jacobson and Truax [12] proposed the use of a reliable change (RC) index. The RC index defines the range in which an individual score is likely to fluctuate because of the imprecision of the measuring instrument. Although this index controls for test-retest reliability, it makes no correction for practice effects, which are an independent source of error [9]. Subsequently, Chelune and associates [13] used the RC index method, with the addition of a correction for observed practice effects on each measure. Chelune and associates proposed that the RC method, corrected for practice effects, addresses the limitations of the traditional arbitrary cutoff techniques by providing clear-cut, statistically sound criteria that define whether an individual’s posttreatment change score exceeds the variation attributable to test reliability and practice effects.

The aim of the present study was to contrast the incidence of immediate postoperative neuropsychologic impairment obtained with the RC and SD methods to illustrate the variation produced by failure to account for measurement error and practice effects.

	Material and methods

Top Abstract Introduction Material and methods Results Comment Acknowledgments References

 
Patients
From 74 patients who underwent isolated elective CABG performed by a single surgeon (J.L.K.) between January 23, 1996, and October 21, 1996, a final sample of 50 patients were included in the study. Of the 24 patients who were excluded, 11 declined participation, 8 did not receive complete neuropsychologic examinations because of time constraints (no medical incapacity), 2 had a past history of cerebral disease, 1 had insufficient English proficiency, 1 was too ill to undergo postoperative testing (low output syndrome), and 1 died after operation (heart failure). The participating patients, after giving their written informed consent, underwent either a hypothermic or normothermic surgical procedure.

Control subjects
Twenty-four unpaid volunteers were recruited from bowling clubs, senior citizens groups, and the Flinders Medical Centre Volunteers Service. Volunteers were ineligible for inclusion in the study if they had a past history of cardiac operation, if they had a neurologic injury or disease, or if they did not speak English as their first language. The demographic and baseline neuropsychologic data for both the patients and the control subjects are presented in Table 1.

Neuropsychologic examination
Patients were tested individually by qualified examiners (A.C.K. and M.J.A.) on the day before operation and then before hospital discharge. All control subjects were tested on two occasions, 7 days apart. The same examiner always was used for the two testing sessions of a given patient or control subject. All patients and control subjects were tested individually in the examiner’s office, free of distractions. Neuropsychologic test selection was based substantially on the Statement of Consensus [8]. The test battery in order of administration was as follows: California Verbal Learning Test (CVLT) [14], Purdue Pegboard (Peg R, Peg L, Peg RL) [15], Controlled Oral Word Association Test (COWAT, initial letter verbal fluency) [16], Trail Making Test (TMT A and TMT B) [17], Wechsler Adult Intelligence Scale-Revised (WAIS-R) Digit Symbol subtest (Dig Symb) [18], Boston Naming Test (BNT) [19], and National Adult Reading Test-Revised (NART-R, administered only at baseline) [20]. All tests were administered and scored in a standardized manner.

The CVLT is able to generate numerous measures of various aspects of learning and memory. However, in the present study, we elected to analyze three measures comprising learning (Tot: the sum of the number of words recalled on trials 1 through 5) and recall (Long Free: the number of words recalled after a 20-minute delay, and Long Cued: the number of words recalled after a 20-minute delay with category cues provided). To minimize practice effects on the CVLT, alternate test forms [21] were administered at the preoperative and postoperative examinations. Every second patient or control subject was administered the alternate form first.

Methods of defining postoperative neuropsychologic change
Two statistical methods for defining postoperative changes on neuropsychologic measures were used and compared directly with one another.

Reliable change indices
Using the methodology outlined by Jacobson and Truax [12], an RC index was calculated for each neuropsychologic measure using the baseline and follow-up data of the control subjects. First, the test-retest reliability coefficient (r_xx) was computed for each measure (Pearson correlation between preoperative and postoperative scores), from which the standard error of measurement (SE_m) was calculated using the formula , where SD₁ is the SD of the baseline score. The standard error of the difference (SE_diff) then was calculated using the formula . The standard error of the difference describes the spread of distribution of change scores that would be expected if no actual change had occurred [12]. To establish a 90% RC confidence interval (two-tailed prediction) in which only 5% of cases would be expected to fall above and 5% to fall below the cutoff, the SE_diff was multiplied by ±1.64 SD. A correction representing the practice effect then was added to the two-tailed cutoff points [13]. The practice effect was calculated for each variable as the mean difference between the follow-up and baseline scores. Thus, an RC 90% confidence interval was calculated from this formula for each variable:

The resulting cutoff values were rounded to the nearest whole number outside the 90% RC interval. For each neuropsychologic measure, a postoperative minus preoperative difference score was calculated for each patient. When this score fell outside the RC interval, a statistically significant change in performance on that measure was considered to have occurred.

Standard deviation method
Using the traditional SD method [5], a postoperative change on a neuropsychologic measure was considered to have occurred if a patient’s change score equaled or exceeded 1 SD of the group mean preoperative score on that measure.

Data analysis
Statistical analyses were performed using the SPSS statistical software package (SPSS Inc, Chicago, IL), with an alpha of 0.05 considered statistically significant. When comparing quantitative data, one-way analysis of variance was used, with the Bonferroni correction (alpha/number of contrasts) applied to control for multiple comparisons [22]. Categorical data were analyzed with the ² statistic. Fisher’s two-tailed exact test was used when the expected cell sizes were small. To examine practice effects, differences between a control subject’s preoperative and postoperative scores were analyzed with paired t tests. Sign tests were used to compare the number of patients who showed postoperative deficits as classified according to the RC and SD methods [23]. This study was approved by the Clinical Investigation Committee of the Flinders Medical Centre (approval number 136/94).

	Results

Top Abstract Introduction Material and methods Results Comment Acknowledgments References

 
Analysis of population demographics and preoperative neuropsychologic data revealed no statistically significant differences among the three groups. Similarly, there were no statistically significant differences between the surgical variables for the two surgical groups. The lack of any differences between the two surgical groups allowed us to collapse these groups for all further analyses.

Reliable change indices
The data obtained from control subjects that were used in calculating the RC indices are summarized in Table 2. All the measures showed acceptable test-retest reliability, with a range from 0.67 (TMT A) to 0.94 (Dig Symb). Statistically significant practice effects were observed on the CVLT Long Free, TMT A, TMT B, Dig Symb, and BNT measures. It is of interest that not all practice effects demonstrated an improvement on retesting. All three CVLT measures showed a decline from baseline to retesting, and the decline was statistically significant on the Long Free measure. To control for this learning bias, the RC indices were corrected by adding the practice effect and were rounded to the nearest whole number outside the 90% interval to obtain the RC intervals (Table 2). The practice effect on some measures was negligible; thus, the RC interval effectively did not differ from the uncorrected RC index.

	Comment

Top Abstract Introduction Material and methods Results Comment Acknowledgments References

 
The aim of this study was to clarify existing discussion regarding how to define the incidence of impairment after CABG by providing clear-cut criteria that are both psychometrically and statistically sound. The principal finding to emerge was that when measurement error and practice effects are not taken into account, the calculated incidence of neuropsychologic impairment can vary significantly. This was demonstrated for the RC and SD methods of impairment criteria, in which the different classifications yielded large, statistically significant differences in the percentage of patients undergoing CABG who showed a postoperative decline on many of the neuropsychologic measures we reported. The SD method defined fewer patients as impaired than the RC method on most of the neuropsychologic measures. This result is consistent with previous research [12, 13] that compared the RC method against standard inferential statistics (uncorrected for measurement error and practice effects), and it confirms suspicions that the traditional methods of defining neuropsychologic sequelae of CABG tend to provide a lower estimate of incidence figures [5, 6].

Both the RC method and fixed cutoff methods (ie, the SD method) serve as statistical conventions for defining change [5, 12]. However, the latter approaches fail to take into account a test instrument’s susceptibility to practice effects and its test-retest reliability. The potential for serious misclassification brought about by failure to control for these factors is well illustrated on the Dig Symb subtest of the WAIS-R. Using the SD method, no patient was classified as showing a postoperative decline on this measure; using the RC method with correction for practice, 36% of the patients were so classified. If the RC method were used with no correction for practice effects, the percentage of patients classified as impaired would fall to 8%. Because the Dig Symb subtest was highly reliable over a 6-day test-retest interval (r = 0.94), the range of measurement error was narrow. If the reliability of the test were more modest (eg, r = 0.75), the range of measurement error would be broadened, and no patients would have exceeded the cutoff for impairment.

The preceding example supports concerns raised by several investigators [8, 12, 13] that meaningful change can be obscured by any data analysis methods that fail to control appropriately for practice effects and test reliability. Although a recent study attempted to revise the traditional SD method to incorporate practice effects [11], and others have raised the issue of the influence of test-retest reliability [2], the RC method is unique in that it considers the influence of practice effects and test-retest reliability for each measure in an approach that is both psychometrically sound and statistically valid [12, 13]. It is important that both test-retest reliability and practice effects be considered because they have independent effects on the analysis of change data. Test-retest reliability coefficients are based on relative rank ordering on the two administrations of the test. Therefore, a high reliability coefficient could be obtained if all subjects systematically made a mild, moderate, or substantial improvement (or decline) at retesting compared with baseline testing, but maintained their same relative rank ordering at both testing times.

With the use of the RC method, the highest incidences of decline were observed on timed tests of visuomotor speed and attention (TMT B, Dig Symb) and manual dexterity (Pegs R). Deficits in these domains are consistent with the findings of most studies that have investigated the incidence of neuropsychologic impairment after cardiac operations [7, 8].

In the present study, one finding that requires further discussion is the negative practice effects displayed by control subjects on the CVLT. We elected to use the CVLT as a list learning task instead of the Rey Auditory Verbal Learning Test as recommended by the Consensus [8]. The CVLT has equal or superior alternate form test-retest reliability on key measures [21, 24, 25] and it measures many more parameters of learning and memory that can be analyzed to define specific subtypes of impairment [14]. The three CVLT measures used in this study were selected on the basis of their robust test-retest reliability coefficients [21]. Although the negative practice effects in the control subjects were not consistent with the positive practice effects displayed on the other neuropsychologic measures, the alternate form of the CVLT was designed specifically such that practice effects would be minimized [21]. Therefore, because the control subjects were not expected to show any improvement on their retest scores, the small decline experienced by the group falls within the overall expectations of the test. Another finding unique to the CVLT measures was the trend for the SD method to classify more patients as declined than the RC method. This tendency is related in part to the negative practice effects displayed by the control subjects.

One aspect of our study limits its comparison with other studies [1–4, 6]: we have not proposed a single overall incidence value for neuropsychologic impairment after CABG. Although such single figures superficially provide a convenient summation of the extent of acquired impairment, it must be recognized that they are calculated by imposing another arbitrary statistical decision on individual test measures. As such, overall incidence data will vary according to which statistical criteria are used [6], as well as with the sensitivity of the tests, the number of tests used, and the range of cognitive domains they assess [8]. Notwithstanding concerns about the accuracy of overall impairment data, any approach that essentially dichotomizes patients as "impaired" or "unimpaired" promotes a one-dimensional view of brain dysfunction [26].

The main concern regarding the use and application of the RC method in this clinical population is the requirement that the indices be derived from an appropriate control group. There is much debate regarding the most appropriate control group for comparison with patients undergoing CABG [5]. The use of a nonsurgical control group enabled us to assess practice effects and the reliability of the measures. Nonsurgical control subjects have been reported previously in the literature [27, 28] and represent an improvement over the single-group incidence study protocol. However, this strategy does not account for the potentially dramatic short-term effects of major operations. The difficulty in using a surgical control group lies with matching the control group to the patients undergoing extracorporeal circulation.

In conclusion, we believe the RC method is a more valid and theoretically sound statistical approach to defining neuropsychologic change after CABG than the traditionally used fixed, arbitrary cutoff methods, which fail to control for test reliability and practice effects. We propose the use of the RC method as a standardized approach to defining acquired neuropsychologic deficits after cardiac operations.

	Acknowledgments

Top Abstract Introduction Material and methods Results Comment Acknowledgments References

 
This work was supported by grants from the National Heart Foundation and the Royal Australian College of Surgeons. We thank members of the Marion Bowling Club, the Marion Probus Club, and the Flinders Medical Centre Volunteers Service for participating as control subjects. We also thank Associate Professor John R. Crawford for early assistance in this study.

	References

Top Abstract Introduction Material and methods Results Comment Acknowledgments References

 

1. Nevin M., Colchester A.C.F., Adams S., Pepper J.R. Evidence for involvement of hypocapnia and hypoperfusion in aetiology of neurological deficit after cardiopulmonary bypass. Lancet 1987;2:1493-1495.[Medline]
2. Shaw P.J., Bates D., Cartlidge N.E.F. Early intellectual dysfunction following coronary bypass surgery. Q J Med 1986;58:59-68.
3. Jenkins C.D., Stanton B.-A., Savageau J.A., Denlinger P., Klein M.D. Coronary artery bypass surgery: physical, psychological, social, and economic outcomes six months later. JAMA 1983;250:782-788.[Abstract/Free Full Text]
4. Newman S., Smith P., Treasure T., Joseph P., Ell P., Harrison M. Acute neuropsychological consequences of coronary artery bypass surgery. Curr Psychol Res Rev 1987;6:115-124.
5. Newman S.P. Analysis and interpretation of neuropsychologic tests in cardiac surgery. Ann Thorac Surg 1995;59:1351-1355.[Abstract/Free Full Text]
6. Mahanna E.P., Blumenthal J.A., White W.D., et al. Defining neuropsychological dysfunction after coronary artery bypass grafting. Ann Thorac Surg 1996;61:1342-1347.[Abstract/Free Full Text]
7. Newman S.P. The incidence and nature of neuropsychological morbidity following cardiac surgery. Perfusion 1989;4:93-100.
8. Murkin J.M., Newman S.P., Stump D.A., Blumenthal J.A. Statement of consensus on assessment of neurobehavioral outcomes after cardiac surgery. Ann Thorac Surg 1995;59:1289-1295.[Free Full Text]
9. McCaffrey R.J., Ortega A., Orsillo S.M., Nelles W.B., Haase R.F. Practice effects in repeated neuropsychological assessments. Clin Neuropsychol 1992;6:32-42.
10. Mills S.A., Prough D.S. Neuropsychiatric complications following cardiac surgery. Semin Thorac Cardiovasc Surg 1991;3:39-46.[Medline]
11. McKhann G.M., Goldsborough M.A., Borowicz L.M., et al. Cognitive outcome after coronary artery bypass: a one-year prospective study. Ann Thorac Surg 1997;63:510-515.[Abstract/Free Full Text]
12. Jacobson N.S., Truax P. Clinical significance: a statistical approach to defining meaningful change in psychotherapy research. J Consult Clin Psychol 1991;59:12-19.[Medline]
13. Chelune G.J., Naugle R.I., Luders H., Sedlak J., Awad I.A. Individual change after epilepsy surgery: practice effects and base-rate information. Neuropsychology 1993;7:41-52.
14. Delis D.C., Kramer J.H., Kaplan E., Ober B.A. California Verbal Learning Test: manual. San Antonio: Psychological Corporation, 1987.
15. Tiffin J. Purdue Pegboard examiner’s manual. Rosemont, IL: London House, 1968.
16. Borkowski J.G., Benton A.L., Spreen O. Word fluency and brain damage. Neuropsychologia 1967;5:135-140.
17. Armitage S.G. An analysis of certain psychological tests used for the evaluation of brain injury. Psych Monographs 1946;60:277.
18. Wechsler D. Wechsler Adult Intelligence Scale-Revised: manual. New York: Psychological Corporation, 1981.
19. Kaplan E.P., Goodglass H., Weintraub S. The Boston Naming Test, 2nd ed. Philadelphia: Lea & Febiger, 1983.
20. Crawford J.R. Current and premorbid intelligence measures in neuropsychological assessment. In: Crawford J.R., Parker D.M., McKinlay W., eds. A handbook of neuropsychological assessment. London: Erlbaum, 1992:267-291.
21. Delis D.C., McKee R., Massman P.J., Kramer J.H., Kaplan E., Gettman D. Alternate form of the California Verbal Learning Test: development and reliability. Clin Neuropsychol 1991;5:154-162.
22. Rosenthal R., Rosnow R.L. Contrast analysis: focused comparisons in the analysis of variance. Cambridge: Cambridge University Press, 1985:45-46.
23. Siegel S., Castellan N.J. Nonparametric statistics for the behavioral sciences, 2nd ed. New York: McGraw-Hill, 1988.
24. Geffen G.M., Butterworth P., Geffen L.B. Test-retest reliability of a new form of the Auditory Verbal Learning Test (AVLT). Arch Clin Neuropsychol 1994;9:303-316.[Medline]
25. Ryan J.J., Geisser M.E., Randall D.M., Georgemiller R.J. Alternate form reliability and equivalency of the Rey Auditory Verbal Learning Test. J Clin Exp Neuropsychol 1986;8:611-616.[Medline]
26. Lezak M.D. Neuropsychological assessment, 3rd ed. New York: Oxford University Press, 1995.
27. O’Brien D.J., Bauer R.M., Yarandi H., Knauf D.G., Bramblett P., Alexander J.A. Patient memory before and after cardiac operations. J Thorac Cardiovasc Surg 1992;104:1116-1124.[Abstract]
28. Townes B.D., Bashein G., Hornbein T.F., et al. Neurobehavioural outcomes in cardiac operations: a prospective controlled trial. J Thorac Cardiovasc Surg 1989;98:774-782.[Abstract]

This article has been cited by other articles:

				P. J. Tully, R. A. Baker, J. L. Knight, D. A. Turnbull, and H. R. Winefield Neuropsychological Function 5 Years after Cardiac Surgery and the Effect of Psychological Distress Arch Clin Neuropsychol, October 29, 2009; (2009) acp082v1. [Abstract] [Full Text] [PDF]

				P. A. Barber, S. Hach, L. J. Tippett, L. Ross, A. F. Merry, and P. Milsom Cerebral Ischemic Lesions on Diffusion-Weighted Imaging Are Associated With Neurocognitive Decline After Cardiac Surgery Stroke, May 1, 2008; 39(5): 1427 - 1433. [Abstract] [Full Text] [PDF]

				F. D. Rubens, M. Boodhwani, and H. Nathan Interpreting studies of cognitive function following cardiac surgery: a guide for surgical teams Perfusion, May 1, 2007; 22(3): 185 - 192. [Abstract] [PDF]

				P. D Raymond, M. Radel, M. J Ray, A. D Hinton-Bayre, and N. A Marsh Investigation of factors relating to neuropsychological change following cardiac surgery Perfusion, January 1, 2007; 22(1): 27 - 33. [Abstract] [PDF]

				E. Farag, G. J. Chelune, A. Schubert, and E. J. Mascha Is depth of anesthesia, as assessed by the bispectral index, related to postoperative cognitive dysfunction and recovery? Anesth. Analg., September 1, 2006; 103(3): 633 - 640. [Abstract] [Full Text] [PDF]

				M. S. Lewis, P. Maruff, B. S. Silbert, L. A. Evered, and D. A. Scott Detection of Postoperative Cognitive Decline After Coronary Artery Bypass Graft Surgery is Affected by the Number of Neuropsychological Tests in the Assessment Battery Ann. Thorac. Surg., June 1, 2006; 81(6): 2097 - 2104. [Abstract] [Full Text] [PDF]

				S. K. Bhudia, D. M. Cosgrove, R. I. Naugle, J. Rajeswaran, B.-K. Lam, E. Walton, J. Petrich, R. C. Palumbo, A. M. Gillinov, C. Apperson-Hansen, et al. Magnesium as a neuroprotectant in cardiac surgery: A randomized clinical trial J. Thorac. Cardiovasc. Surg., April 1, 2006; 131(4): 853 - 861. [Abstract] [Full Text] [PDF]

				P. D. Raymond, A. D. Hinton-Bayre, M. Radel, M. J. Ray, and N. A. Marsh Assessment of statistical change criteria used to define significant change in neuropsychological test performance following cardiac surgery Eur. J. Cardiothorac. Surg., January 1, 2006; 29(1): 82 - 88. [Abstract] [Full Text] [PDF]

				A Collie, P Maruff, M Makdissi, M McStephen, D G Darby, and P McCrory Statistical procedures for determining the extent of cognitive change following concussion Br. J. Sports Med., June 1, 2004; 38(3): 273 - 278. [Abstract] [Full Text] [PDF]

				B. S. Silbert, P. Maruff, L. A. Evered, D. A. Scott, M. Kalpokas, K. J. Martin, M. S. Lewis, and P. S. Myles Detection of cognitive decline after coronary surgery: a comparison of computerized and conventional tests Br. J. Anaesth., June 1, 2004; 92(6): 814 - 820. [Abstract] [Full Text] [PDF]

				O. A. Selnes, M. A. Grega, L. M. Borowicz Jr, R. M. Royall, G. M. McKhann, and W. A. Baumgartner Cognitive changes with coronary artery disease: a prospective study of coronary artery bypass graft patients and nonsurgical controls Ann. Thorac. Surg., May 1, 2003; 75(5): 1377 - 1386. [Abstract] [Full Text] [PDF]

				D. Whitaker The use of Z scores in assessing neuropsychological change after cardiac operations Ann. Thorac. Surg., March 1, 2003; 75(3): 1066 - 1066. [Full Text] [PDF]

				A. Collie, D. G. Darby, M. G. Falleti, B. S. Silbert, and P. Maruff Determining the extent of cognitive change after coronary surgery: a review of statistical procedures Ann. Thorac. Surg., June 1, 2002; 73(6): 2005 - 2011. [Abstract] [Full Text] [PDF]

				D. van Dijk, A. M. A. Keizer, J. C. Diephuis, C. Durand, L. J. Vos, and R. Hijman Neurocognitive dysfunction after coronary artery bypass surgery: A systematic review J. Thorac. Cardiovasc. Surg., October 1, 2000; 120(4): 632 - 639. [Abstract] [Full Text] [PDF]

				E. F. Bruggemans, F. J.R. van de Vijver, and H. A. Huysmans Defining neuropsychological deterioration after cardiac surgery Ann. Thorac. Surg., January 1, 1999; 67(1): 297 - 297. [Full Text] [PDF]

				A. C. Kneebone, M. J. Andrew, R. A. Baker, and J. L. Knight Reply Ann. Thorac. Surg., January 1, 1999; 67(1): 297 - 298. [Full Text] [PDF]

				M. J. Andrew, R. A. Baker, A. C. Kneebone, and J. L. Knight Neuropsychological dysfunction after minimally invasive direct coronary artery bypass grafting Ann. Thorac. Surg., November 1, 1998; 66(5): 1611 - 1617. [Abstract] [Full Text] [PDF]

This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): John L. Knight Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Kneebone, A. C. Articles by Knight, J. L. Search for Related Content PubMed PubMed Citation Articles by Kneebone, A. C. Articles by Knight, J. L.