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Practice effects in repeated neuropsychological assessmentsRobert J. McCaffreya; Albert Ortegaa; Susan M. Orsilloa; Wendy B. Nellesa; Richard F. Haasea

a The University at Albany, State University of New York,

To cite this Article McCaffrey, Robert J. , Ortega, Albert , Orsillo, Susan M. , Nelles, Wendy B. and Haase, Richard F.(1992)'Practice effects in repeated neuropsychological assessments', The Clinical Neuropsychologist, 6: 1, 32 — 42To link to this Article: DOI: 10.1080/13854049208404115URL: http://dx.doi.org/10.1080/13854049208404115

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The Clinical Neuropsychologist 1992, Vol. 6, No. 1, pp. 32-42

092@-1637/92/0601-0032$3.00 0 Swets & Zeitlinger

CLINICAL ISSUES

Practice Effects in Repeated Neuropsychological Assessments

Robert J. McCaffrey, Albert Ortega, Susan M. Orsillo, Wendy B. Nelles, and Richard F. Haase The University at Albany, State University of New York

ABSTRACT

The magnitude of the practice effects associated with repeated administration of the same neurops ychological assessment instruments was examined. In two separate research protocols, subjects were administered their respective battery of neuropsychological instruments twice within 7 to 10 days prior to the initiation of any experimental manipulations. Factors of interest included the test-retest reliability correlation coef- ficients, the magnitude of practice effects, and the intercorrelation matrices among the instruments. In general, the test-retest reliabilities of the neuropsychological instruments were consistent with those found in the general psychological assessment literature. The magnitude of practice effects was greatest on the Logical and Figural Memory Subtests of the Wechsler Memory Scale in both protocols. The intercorrelation matrices may be useful in planning sample sizes for future studies since estimates of statistical power will require the consideration of the intercorrelations among groups of dependent variables.

Neuropsychologists working in either a clinical or research capacity may be called upon to perform serial neuropsychological assessments in order to moni- tor the progression of a disease process, to evaluate the efficacy of a therapeutic agent, or to assess the impact of a rehabilitation program. An important factor in any type of serial assessment is the variance attributable to practice effects. Repeated administration of the same assessment instrument may lead to incre- ments in a patient’s performance attributable to the effects of practice alone. In general, instruments that have a speeded component, require an infrequently

Preparation of the article was supported in part by National Institutes of Health Grants HL-35112 and NS-25006 to Robert J. McCaffrey. Reprint requests to: Robert J. McCaffrey, Department of Psychology, The University at Albany, State University of New York, 1400 Washington Avenue, Albany, NY 12222, USA.

Accepted for publication: April 2, 1991.

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PRACTICE EFFECTS 33

practiced response, or that have a single, easily conceptualized solution are likely to result in significant practice effects (Dodrill & Troupin , 1975). Among brain- injured patients, significant practice effects are reported to occur frequently, while large test to retest changes are reported not to be common among neurologically intact subjects (Lezak, 1982). The majority of the neuropsychological literature on practice effects in normals has focused on the subtests of the Wechsler Adult Intelligence Scale (Matarazzo, 1972; Matarazzo, Carmody, & Jacobs, 1980; Shatz, 1981). There is little normative information on practice effects associated with most neuropsychological instruments for the general population (Gill, Reddon, Stefanyk, & Hans, 1988; Maxwell & Niemann, 1984; Maxwell, Wise, Pepping, & Townes, 1984; Wilson, Wilson, Iacoviello, & Risucci, 1982) and very little for actual patient populations (desRosiers & Kavanagh, 1987).

The psychological assessment literature contains data on the test-retest reliability of virtually all of the instruments used to assess cognitive/behavioral performance, almost without exception, however, only reliability coefficients are reported (e.g., Brown, Rourke, & Cicchetti, 1989; Matarazzo, Wiens, Matarazzo, & Manaugh, 1973; Su & Yerxa, 1984). Psychometrically, this is useful information; however, i t is meaningless in terms of evaluating practice effects. For example, a reliabil- ity coefficient of .98 could be obtained if the subjects systematically made a mild, moderate, or substantial increase (or decrease) in performance at the retest compared to the initial test but maintained their same relative rank order on the two administrations of the instrument. Statistically, Shatz (1981) has suggested that the standard error of measurement be used to set up confidence intervals around an individual patient’s score in order to partial out practice effects from other factors related to improvement in patient’s performance across assessments (e.g., recovery of function following a CVA). Another technique involves the use of equated alternate forms of the same instruments. For many neuropsychological assessments, however, these are not available. In addition, Anastasi (1988) points out the gains may also occur at retesting using parallel forms (i.e., the test sophistication effect). In general, these gains are reported to be smaller than those obtained using the same form of an instrument.

Another alternative is to administer the entire neuropsychological battery twice, in order to assess for the degree of practice effects and to obtain a baseline level of performance. The second administration of the neuropsychological bat- tery is used as a baseline for comparison against subsequent assessments. The initial administration of the neuropsychological battery then serves as a meth- odological procedure to reduce the influence of practice effects.

The present study reports on the general issue of practice effects based on two separate ongoing research projects. The selection of the instruments contained in each of the neuropsychological batteries was based on specific research questions. Despite differences between the two subject populations and the neuropsychological batteries, important information regarding test-retest reliability, the degree of practice effects and the intercorrelations among the neuropsychological instruments is presented.

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34 ROBERT J. MCCAFFREY ET AL.

METHOD

Subjects The first project involved an examination of the neuropsychological and physical side- effects of the beta-adrenergic blocker, metoprolol, using a double blind placebo control- led crossover experimental design (McCaffrey, McCoy, Haase, Ortega, & Orsillo, 1990). Twenty-five newly diagnosed, untreated, mild, essential hypertensives (DBP = 90-105 mm Hg) volunteered as subjects. There were 17 males and 8 females with an average age of 50.1 years (SD = 14.0) and 14.1 (SD = 2.9) years of education. The second project was designed to evaluate the neuropsychological sequelae of prophylactic cranial irradiation therapy in patients with small cell lung cancer who presented with no evidence of CNS metastases (McCaffrey et al., 1990). As a control for the influence of pulmonary disease in the cancer patients, the control group was comprised of chronic cigarette smokers. Thirty-three chronic cigarette smokers with a mean consumption of 1.3 packs per day (SD = 0.5) and a mean smoking history of 38.6 years (SD = 12.2) were recruited from the community and paid $50 for their participation. In the smoker group, there were 15 males and 18 females with a mean age and educational level of 59.1 (SD = 9.3) and 14.9 (SD = 3.4) years, respectively.

Apparatus and Procedure For both groups, the subjects were administered their respective neuropsychological bat- tery twice, within 7 to 10 days. The same assessor was used to evaluate the same subject at both the test and retest assessments. This procedure was employed in order to reduce the confounding influence of practice effects.

The rationale for the selection of the neuropsychological instruments was determined by the requirements of the separate research questions. The instruments in each of the neuropsychological batteries are presented in Tables I and 2 and are described in Lezak (1983), except for the following tests. The Span of Attention Test (Kay, 1982) deals with the ability to sustain focused alertness on a task which makes minimal demands on higher cognitive processes. The test consists of a single 8 1/2 x 11 inch page filled with 500 “X”s arranged in 25 rows of 20 Xs, each separated by a dash (e.g., X-X-X ...). The instructions are to circle as many Xs as possible in 400 seconds. The Math and Reading tests were obtained from the University of the State of New York, Regents High School examination, Competency Tests. The versions used were from prior forms of the Regents Competency Test. The Math test involved 20 untimed arithmetic problems. The Reading test involves a passage that is read aloud by the teacher to the students followed by 10 multiple choice questions. The test was modified by having the subjects read the passage themselves and then answer the questions without the aid of the passage. The Static Motor Steadiness Test manufactured by Lafayette Instruments Company (#30211) consisted of having the subject hold a metal stylus in each of four holes of decreasing diameter (0.3 12,O. 187, and 0.125 in.) for separate 15-second trials. The score was the total number of times the stylus came in contact with the diameter of each hole. Simple Auditory Reaction Time was obtained using a Lafayette Instruments Company Choice Reaction Time Apparatus (#63035) and a ClocWCounter (#54035) set at .001 seconds. The reaction time was the average of 30 trials following 5 practice trials.

The neuropsychological instruments were administered and scored using their stand- ardized instructions, except for the following. In order to decrease the amount of uncon- trolled variance attributable to assessor differences in the administration and the scoring of the Logical Memory portions of the Wechsler Memory Scale (Wechsler, 1945). the paragraphs were tape recorded and the instructions and recorded paragraphs played to each subject. For research purposes, subjects were informed that there would be a delayed recall (Russell, 1975) of the Logical and Figural Memory Subtests of the Wechsler Memory Scale at each of the two assessments. The subject’s recall of the Logical Memory, imme-

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PRACTICE EFFECTS 35

diate and delayed, was tape recorded for subsequent verbatim transcription and scoring using Prigatano’s (1978) criteria. The Digit Span Subtest of the WAIS and the Paired- Associate Learning Subtest of the Wechsler Memory Scale were also presented via tape recordings. Since the responses to these two subtests are not as complex as those to the Logical Memory component, the responses were recorded on prepared assessment forms.

Table 1 .Test-retest reliability and practice effects associated with select neuropsychological instruments in essential hypertensives at the practice effects (PE) and baseline (BL) assessments.

Wechsler Memory Scale Logical Memory

Immediate Recall 25 .61 10.23 (3.14) Delayed Recall 25 .74 8.55 (2.65)

Figural Memory Immediate Recall 24 .63 1 1.17 (3.14) Delayed Recall 24 .74 10.08 (3.51)

Paired Associates 25 .53 10.88 (2.73)

Trail Making Test Part A 25 .80 35.75 (12.81) Part B 24 .92 91.60 (49.83)

Grooved Pegboard Test Preferred Hand 25 .85 83.32 (21.31) Nonpreferred Hand 24 .82 90.00 (20.57)

Finger Oscillation Test Preferred Hand 24 5 8 54.67 (11.55) Nonpreferred Hand 24 .82 50.35 (10.95)

Span of Attention 24 .78 320.15 (74.29)

WAIS-R Digit Span Forward 24 .78 8.44 (2.10) Backward 24 .85 7.44 (2.58)

Math Test 24 3 9 14.08 (4.31)

Reading Test 25 .87 5.12 (2.91)

12.36 (2.75) 4 . 0 3 (C.005) 11.34 (3.39) -6.12 (<.0005)

12.17 (2.18) -2.00 (c.05) 11.70 (2.37) -3.3 (<.005)

12.21 (2.39) -2.7 (C.01)

33.86 (14.98) 1.05 (c.152) 87.08 (53.03) 1.31 (<.lo)

78.91 (26.92) 1.56 (c.06) 81.59 (15.79) 3.47 (<.005)

55.94 (10.50) 4 . 6 4 (<.263) 49.78 (10.22) 0.44 (<.332)

314.53 (70.12) 0.57 (<.286)

8.70 (2.69) -0.85 (<.202) 8.13 (3.06) -1.80 (<.042)

15.17 (4.05) -2.10 (<.025)

5.56 (3.11) -1.41 (<.085)

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36 ROBERT I. MCCAFFREY ET AL.

RESULTS

The test-retest reliability ( rJ and the statistical magnitude of the practice effects are presented in Tables 1 and 2 for the qssential hypertensive and chronic smoker groups, respectively. The test-retest reliability ( rJ of each of the neuropsychological instruments was evaluated by calculating Pearson-Product Moment correlations. The correlations ranged from 0.53 to 0.92 among the sample of essential hypertensives and 0.47 to 0.89 for the chronic smokers.

The magnitude of practice effects were examined by computing one-tailed, dependent group, t tests for each of the instruments. The use of the t tests was to document the magnitude of the practice effects. The p values presented in Table 1 and 2 indicate the magnitude of the obtained practice effects.

Table 2.Test-retest reliability and practice effects associated with select neuropsychological instruments in chronic smokers at the practice effects (PE) and baseline (BL) assessments.

Chronic Smokers

Wechsler Memory Scale Logical Memory Immediate Recall 33 .47 9.68 (3.38) 11.12 (3.26)-2.42 (C.025) Delayed Recall 32 .68 8.09 (2.93) 10.55 (2.98)-5.93 (<.0005)

Figural Memory Immediate Recall 32 .53 9.70 (2.94) 11.19 (2.87)-2.98 (<.001) Delayed Recall 32 .69 8.94 (3.50) 11.03 (2.95)-4.43 (<.0005)

Trail Making Test Part B 32 .49 88.95 (24.52) 74.77 (23.21) 3.27 (c.005)

Grooved Pegboard Test Preferred Hand 32 3 0 82.03 (14.87) 79.66 (14.70) 1.58 (<.06) Nonpreferred Hand 32 .69 88.00 (24.07) 83.44 (15.99) 1.68 (<.05)

Symbol Digit Modulities Test 33 .70 46.88 (9.40) 47.88 (10.96) -.72 (<.24)

Motor Steadiness Test Preferred Hand 33 .59 8.55 (6.63) 7.94 (6.90) .59 (<.28) Nonpreferred Hand 33 3 9 10.71 (9.31) 10.30 (9.68) .54 (<.30)

Speech Sounds Perception Test 33 .83 54.76 (3.03) 55.06 (2.84) -1.01 (c.16)

Seashore Rhythm Test 33 .64 26.42 (3.14) 26.24 (3.25) .39 (<.35)

Simple Reaction Time 33 .62 .37 (.08) .35 (.08) 2.23 (<.025)

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Tabl

e 3.

Inte

rcor

rela

tiona

l m

atrix

of t

he n

euro

psyc

holo

gica

l in

stru

men

ts u

sed

in th

e es

sent

ial h

yper

tens

ive

popu

latio

n at

the

prac

tice

effe

cts/

ba

selin

e as

sess

men

ts.

Inst

rum

ents

~ ~

~ ~

~

LM

I L

MD

FM

I FM

D

PA

TMTA

TM

TB

GPP

G

PN

FOT

P FO

TK

SOA

D

SF

DSB

M

T R

T

Wec

hsle

r M

emor

y Sc

ale

Log

ical

Mem

ory

Imm

edia

te R

ecal

l (L

MI)

-

Del

ayed

Rec

all

(LM

D)

,821

.81

-

Imm

edia

te R

ecal

l (F

MI)

.2

7/ .I

3 .1

8/ 2

5

- D

elay

ed R

ecal

l (F

MD

) .3

5/-.0

6 .1

7/ .I

1 ,7

51.8

4 -

Figu

ral

Mem

ory

Paire

d A

ssac

iatc

r (P

A)

.39/

.11

.24/

.17

.27/

.32

.l8/

.24

-

Tra

il M

akin

g Te

st

Part

A

(TM

TA

) -.1

1/-.0

3 .0

9/ .0

7 -.4

8/-.2

4 -3

-.2

3

-.09/

-.03

- Pa

rt B

(T

MT

B)

-.31/

-.15

-.09/

-.I2

-.47/

-23

-.74/

-.24

-.06/

-.21

.77/

30

-

Cro

ovcd

Peg

booi

d T

est

Pref

erre

d H

and

(GPP

) -.0

6/-.0

9 .1

5/-.I

7 -.0

3/-.I

6 -.3

2/-.0

3 -.2

6/-.O

O

.33/

.47

.55/

51

N

onpr

efm

ed Hand

(GPN

) -.G

9/-.2

5 .0

8/-.2

0 -.2

8/-.3

5 -.5

0/-.3

1 -.2

2/-.I

9 ,4

81.6

4 ,6

51 .6

3

Fing

er O

scill

aiio

n Te

st

- 91

/ .57

-

Pref

errc

dHan

d (F

OT

P)

.24/

32

.0

5/ .

I6 -.OW S

O

,041

.40

.21/

.22

-.20/

-.26

-.14/

-.21

-.35/

-.I6

-.37/

-36

-

Non

prcf

ared

Han

d (F

OT

K)

.24/

.34

.O I/

.I2

,041

.44

.16/

.27

.25/

.27

-.28/

-.32

-. 15

/-.2

1 -.3

4/-.2

3 -.3

4/-.3

5 ,7

61.8

4 -

(TM

TA)

$ 2

(TM

TB)

(FO

TP)

(FO

TN)

Span

ofA

tlenr

ion

(SO

A)

,071

.04

,121

.I7

-331

-.28-

.52/

-.13

.17/

.13

.52/

.41

.52/

34

.4

0/ .2

5 .5

6/ .4

9 -.4

3/-.4

1 -.2

51-3

6 -

(SO

N

WA

IS-R

Dig

it Sp

an

Forw

ard

(DSF

) .2

2/ .I

6 .0

5/ .3

2 .3

7/ .2

8 39

1.3

1 .0

8/ .

19 -.

SO/-.

59

-.55/

-.59

-. 4 w

.29

-.56/

-.45

.28/

30

.1

5/ 2

8 -

.38/

-.22

-

Bac

kwar

d (D

SB)

.26/

.16

.10/

.25

.24/

39

,2

91 3

0

,271

.21

-3-.

53

-.5

3/-.5

7 -.4

1/-.3

4 -.4

8/-3

6 ,4

71.2

4 ,5

01.4

5 -.2

1/-.2

4 ,6

91.6

9 -

Mat

h T

csl

(MT

) .2

0/ .LO

-.08/

2

3

.62/

.53

.49/

.52

.42/

.a -.6

1/-3

6 -.5

6/-.5

5 -.3

7/-2

8 -.4

7/-.4

2 ,1

71 3

4

,381

.29

-.20/

-.05

.55/

.54

,571

.51

- (M

T)

Ren

ding

Tcs

r (R

T)

,041

.04

.07/

.22

.181

.05

.33/

.12 -.09/.04 -.

Lo/

-.M

-.41/

-.44

-.29/

-.35

-.36

/-si

-.2

11-.1

7 -.

ia/-

.u

-.w/-.

o4

.i7/

.07

-.06/

-.07

.121

.18

- (R

T)

Not

e: T

he fi

rst c

orrc

latio

n is

the

prac

tice

effe

cts

corr

elat

ion

for borh

inst

rum

ents

and

lhe

second

Cor

rela

tion

IS rh

e co

rrel

atio

n fo

r bo

th in

stru

men

ts a

t bas

elin

e.

w

4

Downloaded At: 13:33 17 November 2010

Tabl

e 4.

Int

erco

rrel

atio

n m

atrix

of t

he n

euro

psyc

holo

gica

l ins

trum

ents

use

d in

the

chro

nic s

mok

er p

opul

atio

n at

the

prac

tice

effe

ctsh

asel

ine

asse

ssm

ents

.

Inst

rum

ents

~

LMI

LMD

FM

I FM

D

TM

TB

G

PP

GPN

SD

MT

MSP

M

SN

SSPT

SR

T R

T

Wec

hler

Mem

ory

Scal

e Lo

gica

l Mem

ory

Imm

edia

te R

ecal

l &

MI)

D

elay

ed R

ecal

l (L

MD

) .9

4/.6

5 -

-

Figu

ral M

emor

y Im

med

iate

Rec

all

(FM

I)

,551

.24

.58/

.31

-

Del

ayed

Rec

all

(FM

D)

,441

.I7

.52/

.22

.84/

.74

-

Trai

l Mak

ing

Test

Pa

rt B

(TM

TB)

-.33/

.06

-.4

5/-.2

9 -.3

2/-.4

1 -.4

1/-.4

3 -

Gro

oved

Peg

boar

d Te

st

Pref

erre

d H

and

(GPP

) -.3

6/-.2

3 -.4

4/-.3

2 -.3

6/-.3

2 -.4

0/-.4

0 ,3

41.3

2 -

Non

pref

emed

Han

d (G

PN)

-.33/

-.20

-.38/

-.34

-SO

/-.39

-.4

51-.4

3 .2

7/ .3

6 .7

3/ .6

9 -

Sym

bol D

igit

Mod

alif

ies T

est

(SD

MT)

-.34

/-.03

,3

31.1

3 .3

2/ .09

,341

.32

-.31/

-33

-.44/

-.41

-.36/

-.56

-

Mot

or S

tead

ines

s Te

st

Ref

erre

d H

and

(MSP

) -.

09/.2

9 -.0

4/.2

9 -.3

1/.0

9 -.3

41.1

0 -.o

O/-.

oO

,171

-.I4

,171

.14

-.27/

-.33

- N

onpr

efem

ed H

and

(MSN

) .0

7/ .2

6 .1

2/ .2

9 -.

lo/

.02

-.04/

.02

-.2

0/-.0

6 .0

4/ .0

2 -.0

2/ .

I5 -

.18/

-.25

.71/

.79

-

Spee

ch S

ound

s Pe

rcep

tion

Test

(S

SPT)

,2

61.2

5 ,3

71.4

8 .1

9/-.0

2 .2

9/ .1

8 -.4

4/-.2

9 -.3

6/-.3

3 -.1

3/-.4

0 -.2

4/ .

53 -.MI .01

.14/

.03

-

..

!a

(TM

TB)

Seas

hore

Rhy

thm

Tes

t (S

RT)

.3

3/ .1

7 ,3

51.4

5 ,5

21.1

3 .5

8/ .2

5 -.2

1/-.I

8

-.38/

-.12

-.23/

-.37

.46/

.32

-.40/

-.03

-.13/

.06

.2

3/ .3

8 -

(SR

T)

Sim

ple

Rea

ctio

n Ti

me

(RT)

.0

5/-.I

8 ,1

21.0

3 .2

8/-.0

9 -.2

8/-.2

4 -.2

8/-.1

8 -.O

W

.34

.09/ .0

5 -.0

2/-.1

9 -.2

1/ .

03 -.

091

.29 -.09/ .

04

-.30/

.09

- (

RT)

Not

e: T

he fi

rst c

omel

atio

n is

the p

ract

ice

effe

cts c

orre

latio

n fo

r bot

h in

stru

men

ts an

d th

e se

cond

corr

elat

ion

is th

e co

rrel

atio

n fo

r bot

h in

stru

men

ts a

t bas

elin

e.

Downloaded At: 13:33 17 November 2010

PRACTICE EFFECTS 39

The intercorrelation matrices for each of the neuropsychological batteries are presented in Tables 3 and 4 rounded to two decimal places.

In addition to providing useful information about the intercorrelations among the neuropsychological variables, these intercorrelations may prove useful to investigators who anticipate their use in future research as a multivariate set of

Table 5. Test-retest reliability of select neuropsychological instruments from the clinical literature.

Instrument Subjects r,, Test-retest Interval Source

Wechsler Memory Scale Logical Memory

Immediate Recall

Delayed Recall

Figural Memory Immediate Recall

Delayed Recall

Paired Associates

Halstead-Reitan Battery

Trail Making Test Part A

Part R

Finger Oscillation Test

5 1 elderly males .93 26 elderly females .77 30 normals and .a8 75 brain-damaged subjects

51 elderly males .90 26 elderly females .67 30 normals and .51 75 brain-damaged

subjects

51 elderly males .90 26 elderly females .93

29 normal, young males .46 16 elderly patients with .78

diffuse cerebrovascular disease

29 normal. young males .44 16 elderly patients with .67

diffuse cerebrovascular disease

2 4

Speech Sounds Perception Test 29 normal, young males .49

16 elderly patients with .67 diffuse cerebrovascular disease

Seashore Rhythm Test 29 normal, young males .37 16 elderly patienu with .58

diffuse cerebrovascular disease

W N S - R Digif Span 40-80 normals .83

Symbol Digit Modalities Test 80 adults

1 day 1 day reliability determined via Russell (1975) internal consistency method

Meer & Raker (1967)

1 day 1 day reliability determined via Russell (1975) internal consistency method

Mccr & Raker (1975)

1 day 1 day

20 weeks 12.4 weeks

20 weeks 12.4 weeks

20 weeks

20 weeks 12.4 weeks

20 weeks 12.4 weeks

Meer & Baker (1967)

Matarazm et al. (1974)

Matarazzn et al. (1974)

Matarazm et al. (1974)

Matarazm et al. (1974)

Matarazm et al. (1974)

1 to 7 weeks Wechsler (198 1)

4 weeks Smith (1982)

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40 ROBERT 1. MCCAFFREY ET AL.

dependent variables, and who wish to conduct prospective, multivariate power analysis (Cohen, 1988). An estimate of the matrix of intercorrelations among the dependent variables is required for these power computations and the data pro- vided here provide a useful empirical estimate.

Other investigators have examined the test-retest reliability coefficients of several of the neuropsychological assessment instruments included in the present report. These data are summarized in Table 5. As shown in Table 5, the charac- teristics of the samples and the test-retest interval varied considerably among the studies.

DISCUSSION

The values of the test-retest reliability correlation coefficients for the neuro- psychological instrument obtained with the essential hypertensive and chronic smoker samples are consistent with those reported in the general psychological assessment literature (Anastasi, 1986). In both samples, the magnitude of practice effects, as indexed by one-tailed t tests, were greatest for the Logical and Figural Memory subtests of the Wechsler Memory Scale. Among the essential hypertensives considerable practice effects were also obtained on the Paired-Associate Subtest of the Wechsler Memory Scale, the Grooved Pegboard Test-nonpreferred hand, the WAIS-R Digit Span-Backwards and the Math Test. Practice effects for the chronic smokers were observed on the Trail Making Test - Part B, the Grooved Pegboard Test-nonpreferred hand, and the Simple Auditory Reaction Time Test. In both samples, the magnitude of practice effects among the remaining instruments was minimal.

The magnitude of the test-retest correlation coefficients among the chronic smokers were generally lower than those obtained on the same instruments in the sample of essential hypertensives. There are at least three factors which may have contributed to these discrepant findings despite comparable methodologies. First, the chronic smokers were paid volunteers whose primary motivation was financial while the essential hypertensives were unpaid subjects whose motivation focused on knowing the potential impact of their medication on cognitive func- tioning. The second factor is that the chronic smokers’ pulmonary functioning may have been compromised relative to the essential hypertensives. Third, the chronic smokers were significantly older ( t (60) = 9.27, p < .Ol) than the essential hypertensives. Thus, the differences obtained between the two samples may have been due to any one or a combination of these factors.

The test-retest reliability measures of both research samples and those re- ported from various normative data sources in the neuropsychological literature vary considerably reflecting different populations, sampling procedures and test- retest intervals. As such, clinical neuropsychologists must take these factors into consideration when attempting to interpret the data from individual patients.

The primary goal of this report was to acknowledge the differences in test-

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PRACTICE EFFECTS 41

retest reliability across different populations, evaluate the extent of practice ef- fects, and report on the intercorrelations matr ices of a select g roup o f neuropsychological instruments. The latter goal was t o provide data that would b e useful t o investigators planning multivariate studies. Clearly, clinical neuropsychologists need t o expand to the existing data base on the factors noted above. In the interim, both the scientist and practitioner should exercise caution when attempting t o interpret the significance o f practice effects and test-retest reliability coefficients i n repeated neuropsychological assessments.

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