J ournal of Ge ronto lo 9,": P SyCHOLOG IC AL SCI EN C ES
1 9 9 5 ,V o l . 5 0 8 , N o . I , P 3 3 - P 4 l
Coptright I995 bt The CerontokNkvl
Stxiei (,1'Aneri(d
Interrelations
of Age, Health,andSpeed
JulieL. Earlesand Timothy A. Salthouse
Georgia Institute of Technology.
Latent construct structural equation modeling of lhe relations among age, self-rated health, and speed was conducted
with two samples, each containing 372 adults betteeen18 and 87 years of age. The major resulti were confirmed in
both samples. Self-rated health, sensory-motor speed,perceptual speed, and reaction time speedall decreaied as age
increased, but health only partially mediated the relationship between age and speed. There were direct elfects of age
on all types of speed in addition to the indirect effects ofage on speed through the self-rated health measurii, and-thire
were direct effects of age on perceptual speed in addition to the indirect effects through sensory-motor speed.
THERE is growing evidencethat speedis an important
r contributorto the declinein cognitiveperformancethat
occursin many taskswith increasedage (c.f., Salthouse,
1992, 1993a).Many reports now exist indicating that the
age-related
variancein a varietyofcognitivetasks,including
some memory tasks,is greatly reducedafter statisticalcontrol ofan indexofperceptualspeed(Hertzog,1989;Lindenberger,Mayr, & Kliegl, 1993;Salthouse,1993a, 1993b;
Schaie,1989).
Although speedappearsto be importantto the relationship
betweenage and various measuresof cognition, relatively
little is yet known about the sourcesof the relationship
betweenageand speed.Healthstatusis one possiblesource,
or mediating factor, becausehealth presumably reflects
biological factorsthat affect speedof processing.Evidence
concerningthe role of healthin the relationshipbetweenage
and cognitive performancehas been mixed. Increasedage
hasbeenreportedto be associated
with declinesin self-rated
healthstatus(Perlmutter& Nyquist, 1990),and self-rated
health status has been found to be related to cognitive
performance,especiallyfor older adults(Field, Schaie,&
L e i n o , 1 9 8 8 ; H u l t s c hH, a m m e r ,& S m a l l ,1 9 9 3 ;P e r l m u t t e r
& Nyquist, 1990).Salthouse,Kausler,and Saults(1990),
however, found that statisticallycontrolling for self-rated
health statusdid not greatly attenuatethe age-relatedvariancein severalcognitivetasks.One possiblereasonfor the
inconsistencyregarding the influence of health in earlier
researchmay be that the behavioralmeasureswere at too
high a level to exhibit direct health-relatedeffects. More
pronouncedrelationsmay be evident with simpler behavioral measuressuchas thosereflectingthe speedof performing elementarytasks.The goal of the presentproject was to
examinethis hypothesisusing structuralequationmodeling
(i.e., LISREL) methods.
Salthouse(1992, 1993a,1993b,1994)distinguishes
between sensory-motorspeed,reflectingthe speedwith which
a personcan perform the sensory-motoraspectsof the task
such as registeringthe stimuli and producing simple responses,and perceptual-cognitive
speed,correspondingto
the speedwith which a personcan perform taskscontaining
elementarycognitive componentssuch as substitutionor
comparison.He found that the relationshipbetweenageand
perceptualspeedwas still significanteven after controlling
for sensory-motorspeed,and that the age-relatedvariancein
severalcognitivemeasureswasattenuatedmoreaftercontrol
of perceptualspeedthan after control of motor speed.This
pattern is consistentwith the view that perceptualspeedis
composedof sensory-motorprocessesplus cognitive processes,
andthatincreased
ageis associated
with a slowingof
both typesof processes.
Becausereactiontime tasksare frequentlyusedto assess
processingspeed, this project also involved two reaction
time measuresin additionto the motor speedand perceptual
speedmeasuresderived from paper-and-pencil
procedures.
The reactiontime measureswere expectedto be correlated
with the other speedmeasures,
but no specificdirectionof
influencewas hypothesizedbecauseof the differentmethods
(i.e., computeradministration
of assessment
of the reaction
time tasksand paper-and-penciladministrationof the other
speedtasks).
If healthstatusdoescontributeto the age-speed
relations,
then it is importantto identify the factorsresponsiblefor this
influence.In two large, population-based
studies,age has
beenfoundto be associated
with an increasein hypertension
and cardiovascular
disease(Dawber, 1980; Mittelmark et
al., 1993).We, therefore,postulatedthat a major determinantofage-related
variationsin healthstatuswascardiovascularfunctioning.
Although the use of medicationto control hypertension
may reduce or eliminate the effects of hypertensionon
cognition(Farmeret al., 1990),many studieshavereported
that hypertensionand cardiovasculardiseaseare negatively
relatedto cognitivefunctioning(Elias,Robbins,Schultz,&
Pierce, 1990; Elias, Wolf, D'Agostino, Cobb, & White,
1993;Farmeret al., 1990;Franceschi,Tancredi,Smirne,
Mercinelli, & Canal, 1982;Hertzog,Schaie,& Gribbon,
1978; Schultz, Elias, Robbins, Streeten,& Blakeman,
1986), and to measuresof perceptualspeed(Boller, Vrtunski, Mack, & Kim, 1911; Light, 1978; Speirh, 1964,
1965). There is also evidencethat speedmay be more
affectedby hypertensionthan are other cognitive abilities
(Shapiro,Miller, King, Ginchereau,& Fitzgibbon,1982;
Wilkie, Eisdorfer,& Nowlin, 1976). Van Swietenet al.
(1991) presentevidencethat hypertensionin older adults
may cause brain damage that causes cognitive decline,
including declinesin speed.We, therefore,postulatedthat
P33
P34
EARLESANDSALTHOUSE
health and cardiovasculardiseasewould partially mediate
the relationbetweenage and speed.
To summarize,the goal of this projectwasto testhypothesized relationsamong age, health status,and severalmeasuresof speed.The datausedin the analyseswere originally
collectedfrom threestudiesreportedby Salthouse(in press).
Becausecompletedatawere availablefroml44 adults,two
separatesampleswere createdto cross-validatethe model
modificationprocess(Breckler,1990).
METHOD
Subjec'ts
Participants
were744 adultsage l8-87 from threeseparate studies. Two hundred and forty-six of the subjects
( 1994)and 258 participarticipated
in Study I of Salthouse
patedin Study 2 of that project. An additional240 subjects
participatedin Study I of Salthouse(in press).All participants were community-dwellingadults recruitedthrough
(requestinghealthy adults) or
newspaperadvertisements
throughcommunitycontacts.They were eachpaid $20 for a
2-3 hour sessioninvolving a battery of cognitive tests
includingthe ones discussedhere. The total data set was
dividedinto two samplesof 372 adults,eachcontaininghalf
of the participantsfrom each study. The mean age of the
i n d i v i d u a l si n S a m p l eI w a s 4 1 . 2 ( S D : 1 6 . 5 ) ,w i t h 1 4 0
subjectsbelow age 40,127 age4G-59,and 105age60 and
above.The meanage in Sample2 was 48.4 (SD : 16.8),
with 127adultsbelow age40, 129 age40-59, and I l6 age
60 and above. Women comprised63.4Voof Sample l, and
60.27oof Sample2. Participants
in SampleI had a meanof
14.4(SD : 2.5) yearsof education,and thosein Sample2
had a meanof 14.7(SD : 2.4) years.
Measures
Only those measuresused in the presentstudy will be
describedhere. (See Salthouse[994] and Salthouse[in
pressl for a completedescriptionof the other tasks.) Five
constructswere measured:self-ratedhealth, cardiovascular
disease,sensory-motorspeed,perceptualspeed,and reaction time speed.(Genderandeducationwerealsoincludedin
initial analyses,but neithervariableaffectedthe age-speed
relations, and thus results with these variablesare not reported.)The variablesare listedin Table l.
Table l. Descriotionof Variables
Age
H e a l t hr a t i n g I ( l : E x c e l l e n t , 5 : P o o r )
Health rating 2 (l : Excellent,5 : Poor)
Satisfactionwith health1l : High, 5 : Low)
5 Health-relatedactivity limitations(l : High, 5 : Low)
6 Surgeryfor cardiovascularproblems(0 = No, I : Yes)
7 Medications or dietary restrictions for cardiovascular problems
(0:No, l=Yes)
8 Boxes (no. in 30 sec)
9 Digit Copy (no. in 30 sec)
l0 Letter Comparison(no. correct- no. incorrectin 30 sec)
I I PatternComparison(no. correct* no. incorrectin 30 sec)
l2 Digit Digit (reciprocal of median responsetime in msec multiplied
by 10,000)
l3 Digit Symbol (reciprocalof median responsetime in msec multiplied
by 10,000)
vascular(heartor artery)problems?" (0 : No, I : Yes);
"Are you currently taking medicationor under dietary
and
restrictionsfor high blood pressure,or haveyou beentreated
for this condition in the past?" (0 : No, I : Yes).
Sensory-motorspeed. - Sensory-motorspeedwas assessedwith measuresfrom two tests.(Seetop of Figure I for
an illustration.)The BoxesTestwas a paper-and-pencil
test
containing100open(i.e., three-sided)
boxes,with subjects
askedto draw a line to completeeachbox. The scorewas the
numberof boxescompletedwithin 30 seconds.
The Digit Copy Test was alsoa paper-and-pencil
test.The
testpagecontained100pairsof boxeswith a digit in the top
box and nothing in the bottom box. The subjectcopied the
digit in the top box into the bottom box, and the scorewas
the numberof digitscopiedin 30 seconds.
Perceptualspeed.- Perceptualspeedwas assessed
with
the two testsillustratedin the bottom of Figure I . The Letter
ComparisonTestcontained2l pairsof letterstringswith 3,
6, or 9 items in each string. If the letter strings were the
same,the subjectwasto write an S on the line betweenthem,
and if they were different (i.e., a changein the identity of
one letter in one memberof the pair), a D was to be written
on the line. Thirty secondswere allowedfor the test, and the
scorewas computedby subtractingthe numberof incorrect
Health. - Four measuresof self-ratedhealth were obresponsesfrom the numberof correctresponses,in order to
tained. A paper-and-pencildemographicsquestionnaireincorrectfor guessing.
cluded three health questions, similar to those used by
The PatternComparisonTest was similar to the Letter
Krause(1990), that were to be answeredusing a 5-point
ComparisonTest, except that the to-be-comparedstimuli
scale.Thesewere: "In general,how satisfiedare you with
were pairsof line patterns.The test pagecontained60 pairs
yourhealth'?"(I : High,5 : Low); "How would you rate
of line patternswith 3, 6, or 9 line segmentsper pattern,and
your healthat the presenttime?" ( I : Excellent,5 : Poor);
30 secondswere allowedto work on the test.The taskwas to
"How
and
muchareyour daily activitieslimited in any way
decideif the pairs were the sameor different (i.e., a change
problems?" ( I : High, 5 :
by your healthor health-related
in the identity of one line segmentin one member of the
Low). Participantsalso ratedtheir healthon a 5-point scale
pair), andto write an S (for same)or a D (for different)on the
(l : Excellent,5 : Poor)in acomputer-administeredtask. line betweenthem. The score was the number of incorrect
responsessubtractedfrom the numberof correctresponses.
CardiovascuLardisease.- The demographicsquestionnaire also includedtwo questionsabout cardiovasculardisReactiontime speed.- Two measuresof reactiontime
ease.Thesewere: "Have you ever had surgeryfor cardiospeedwerealsoobtainedfrom eachresearchparticipant.(See
AGE, HEALTH, ANDSPEED
BOXES
P35
DigitDigit
DIGITCOPYING
DigitSymbol
r f L _ i r -Er rE E E EEBHHBHBHB
EHHEHBEH
l n l l-l l
Ert
EI
f f n l IJ EEEEE
E
N
t-t LI f IJ l
l
nI
l
IJ
EEEEE
EEEEEH
*
;
NO
(zl
YES
(n
Figure 2. Illustrationof sampledisplaysin the reactiontime tasks.
PATTERNCOMPARISON
M_tr
tr_tr
tr_tr
tr_tr
w_g
LETTER
COMPARISON
Bl(\/
BKP
DRSPQ- DRSPQ
MJDWPL-
MJDSWPL
JWS-JXS
XFLKM- XFLKM
QWZPLNV QWZPLNV
Figure l. Samplesof paper-and-pencilspeed tasks. The top two tests
were postulatedto assesssensory-motorspeed,and the bottom two tests
perceptualspeed.
Figure2 for an illustrationof a sampledisplayin eachtask.)
In the Digit Digit Test, a redundantcode table conraining
pairsof identicaldrgitswas presented
at the top of the screen,
and a probestimuluscontaininga pair of digits was presented
in the middleof the screen.The subjectpressedthe "i " key if
thedigits matchedandthe "2" key if thedigitsdid not march.
Eighteenpracticetrials were followed by 90 experimental
trials(i.e., I 0 with eachdigit).Because
average
accuracywas
over95Vo,the dependentvariablein both reactiontime tasks
wasthe medianresponse
time in msec.
In the Digit SymbolTest,thecodetablecontainedpairsof
digitsandsymbols,andtheprobestimuluscontaineda digitsymbol pair. If the digit and symbol matchedaccordingto
the code table, the subjectpressedthe "/" key, and if they
did not matchaccordingto the code table then the "2" key
was pressed.As in the Digit Digit task, l8 practicetrials
precededthe 90 experimentaltrials.
Procedure
Participantswere tested in a single sessionat mutually
convenientlocationssuch as a college campus, churches,
or homes.The order of presentationfor the tasksconsidered
in the presentanalysiswas: Questionnaire,
Boxes, Letter
Comparison,PatternComparison,Digit Copy, Digit Digit,
Digit Symbol.
Rr,sulrs
The mean,standard
deviation,kurtosis,andskewforeach
variablein eachsamplearepresentedin Table 2, andthe correlationmatricesarecontainedin Table3. Kurtosisandskew
valuesare reportedto test the assumptionof multivariate
normality.Kurtosisestimateswerebetween-1 .03 and2.14
for all measuresexcept the cardiovasculardiseasesurgery
measure,Digit Digit, andDigit Symbol.The Digit Digit and
Digit Symbol reactiontime variableswere transformedby
takingthe reciprocaland multiplyingby 10,000in orderto
decreasethe kurtosis and skew of the measures.therefore
increasingnormalityof the distributions.After the transfbrmation,the Digit Digit variablehad a kurtosisof -.09 and a
skewof -.46 for SampleI anda kurtosisof -. l4 andskewof
-.25 for Sample2. The Digit Symbolvariablehada kurtosis
of .46 and a skew of .45 for SampleI and a kurtosisof .01
and skew of .34 for Sample2. Becausethe measuresof
cardiovascular
diseaseweredichotomousand had high kurtosis,this constructwas not usedin the initial model.
Estimatesof the reliabilitiesof the speedmeasuresare
containedin Table4. The immediatereliabilitieswerebased
on conelationsbetweenalternateformsof the testsadministeredin the samesessionfor the 240 adultsbetweenl8 and
82 yearsof age in Study I of Salthouse
(in press).The twomonthreliabilitieswerebasedon a sampleof 39 olderadults
(58 to 80 yearsof age) who were re-administeredthe same
testsapproximatelytwo monthsafter the original testing.
Age Relations
In orderto illustratethe agetrendsfor the speedmeasures,
all measureswere convertedto z-scoresand plotted as a
function of age decadein Figure 3. Nonlinear age effects
were examinedin multiple regressionequationswith quadratic Age and cubic Age terms enteredafter the linear Age
term. Noneof the nonlineareffectsweresignificant(p < .01)
for any of the measuresin Sample l, but the quadraticAge
term was significant(andpositivein direction)for the Boxes,
Digit Copy, and Letter Comparisonmeasuresin Sample2.
Becausethe higher-ordereffects were restrictedto a few
measuresin one sample, and were associatedwith rather
smallincrements
in variance(i.e., l.5Vofor Boxes,5.4Vofor
Digit Copy, and 3.37o for Letter Comparison),only linear
ageeffectswere consideredin subsequent
analyses.
P36
EARLESANDSALTHOUSE
Table2. Summary
Statistics
Sample I
Variable
Mean
SD
l.
2.
3.
4.
5.
6.
7.
8.
9.
10.
I l.
12.
13.
/1
r6 . 5
0.97
0.88
0.84
0.87
0 .l 8
0.39
13.8
lt.4
3.3
4.0
281
446
Age
Health Rating I
Health Rating 2
Health Satisfaction
Health Limit
Surgery
Medications
Boxes
Digit Copy
Letter Comparison
PatternComparison
Digit Digir
Digit Symbol"
1
2.09
2.31
2.34
1.56
0.03
0 .r 9
48.8
51.2
9.9
15.5
822
I 636
Sample2
Kurtosis
Skew
Mean
- 1.03
-0.32
-0.26
0.65
2.t4
26.4
0.64
0.41
-0.02
t.ll
0.51
6.88
t.34
0.29
0.62
0.30
0.51
I.61
5.32
t.62
0.22
-0.21
-0.29
0.47
2.30
r.06
48.4
2.07
2.27
a
1A
1.59
0.05
0 .l 5
48.3
52.0
l0.l
15.6
791
l6t2
- 1.03
- 0 .l 3
-0.30
0.66
1.78
I3 . 8 6
I .75
0.02
0.66
0.79
- 0 .l 6
5.98
t.37
16.8
0.96
0.90
0 . 8l
0.86
0.23
0.36
1 3 I.
10.5
3.4
4.3
235
442
0.05
0.65
0.32
0.50
1.48
3.97
1.93
0.06
-0.43
-0.06
o.42
2.08
1.08
Nrle. Skew and Kurtosiswere computedusing SAS.
"ValuesreDo(ed are for medianreactiontimes in msecbeforethe transformationdescribedin Table I
Table 3. CorrelationMatricesfor Sample I (abovediagonal)and Sample2 (below diagonal)
l0
I
2
3
4
5
6
l
8
9
IO
I I
t2
l3
.19
.09
.t2
.o7
.21
.25
.29
^<
-.45
- .38
-.56
-.49
-.58
.20
.12
.15
.69
.79
. )-J
_):)
t1
.zJ
-.19
-.t5
-.08
-.09
-.14
-.t2
.22
.28
-.18
-.09
ta
ta
-.15
.t4
.65
.80
.54
.15
.21
-.16
-.09
-.02
-.04
- . 1I
-.10
1^
.51
.55
.54
.22
.26
_.15
_ .t 5
-.I8
-. L-)
1a
1^
.06
.01
.02
.00
.02
.29
.24
. z-t
.t7
.16
.l l
.30
-.t4
-.21
-.t4
-.08
-.14
-.t7
_10
*.26
-.28
t l
aa
.01
-.24
-.18
t l
-.20
-.25
-.26
11
-.47
-.29
- .30
ta
a1
.65
.o/
.J:)
.50
.45
.44
.46
.55
ll
*.45
aa
-.25
_.19
-.I8
-.03
11
.45
.56
.50
.36
.47
- ./-)
l2
t3
< )
57
1t
11
a l
-.13
-.24
-.09
a2
.49
.51
.59
5l
60
l)
f1
-.20
-.07
-.27
.31
.39
.50
.54
-.22
-.04
-.29
.38
.42
.59
.61
11
.72
ly'ote:Numbersofvariables correspondto thosein Table l. All correlationswith an absolutevalue greaterthan. l3 were signiticantly(p < .01) different
from zero.
Table 4. Reliabilitiesof SpeedMeasures
lmmediate
Boxes
Digit Copy
Letter Comparison
Pattern Comparison
Digit Digit Time
Digit Symbol Time
.86
.86
.58
.61
.93
2-Month
measureof overall fit that takes into account the degreesof
residualis basedon the
freedom, and the root-mean-square
averageof the unexplainedresiduals.
.t-,
.70
.71
.64
.85
Nole.' Immediatereliabilities are correlationsbetweenalternateforms.
Two-month reliabilitiesare test-retestreliabilities.
CovarianceStucture M odeling
The varianceicovariance
matrix was analyzedusing the
LISREL VII maximumlikelihoodestimationprocedure.For
each model the chi-squarevalue, degreesof freedom, pvalue,adjustedgoodness-of-fitindex, androot-mean-square
residualare reportedas suggestedby Raykov, Tomer, and
(1991).The adjustedgoodness-of-fit
Nesselroade
indexis a
MeasurementModel
A model with four factors (health, sensory-motorspeed,
perceptualspeed,and reactiontime speed)was fit to the data
from Sample I by allowing covariancesamong all of the
factors. The residual variancesof the measureswere also
estimated,but the residualcovarianceswere fixed at zero.
The fit of this model(i.e., Ml) wasadequate,
as indicatedin
Table5.
Age was then addedto the model. As in the first model
(i.e., M l), all of the factorswere allowedto intercorrelate.
The residual variances were estimated, but the residual
covarianceswere setto zero. As can be seenin Table 5, this
model (i.e., M2) alsohad a satisfactoryfit. Thus the hypothesizedfactor structurefit the dataadequately.
Standardizedcovariancesamong health, speed,and age
are in Table 6. It can be seen that ase is associatedwith
P37
AGE, HEALTH, AND SPEED
Sample2
Sample1
t'5
Bon
4tDlglpop'
1
Commbon
Paltern
,...o.,;.
o.
IrECotnFbdr
"o
tb
E
o
8
:'.:t
o
K.*r=,.
o.5
D'ql{,Fr
s'\
--
)?
Dlglt SyFbol ff
-N.--
o
o.' t \
*l
.t
-'-./
1..'-.-r'
'rN
.i\
.lr'b
-1.5
-1.5
n
3
o
4
{
l
5
o
d
t
7
o
8
o
z
'
'
E
)
/
o
s
o
q
)
7
o
o
o
Chronological
Age
Age
Chronological
by between39 and ttl individualsin each
Figure 3. Mean z-scoresby decadefor the six speedmeasuresin the cunent prolect. Eachdecadeis represented
samole.
Table 5. Summaryof Model Fitting for Sample I
Model
Description
X'
df
;;-value
AGFI
RMR
Ml
M2
NI
lnterconelatedfactor structure
Addition of age
Null model
40.48
54.51
732.56
29
35
4s
0'76
.019
000
.960
.952
.549
382
191
I 8.25
Sl
Basic model (seeFigure 4)
Compareto M2
Compareto N I
Add direct path from Health to Pspd
Compareto S I
54.51
0.0
678.05
36
I
9
.953
793
5 4 . 5|
-15
.952
.191
0.0
|
025
>.01
<.01
0l9
>.01
.9-56
.949
.576
.321
.67|
15.55
52
After Addition of CardiovascularDiseaseFactor
M3
M4
N2
factorstructure
Intercorrelated
Additionof ase
Null model
58.38
73.23
808.31
44
5l
66
53
Basicmodel(seeFigure5)
to M4
Compare
Compare
to N2
Add directpathfromAgeto Health
C o m p a rt o
e5 3
Add directpathfromHealthto Mspd
to 53
Compare
AdddirectpathfromHealthto Pspd
to 53
Compare
Add directpathfromHealthto RTspd
to 53
Compare
Add directpathfromCVD to Pspd
to 53
Compare
78.60
5.3'7
729.71
15.36
2.13
76.'71
3.48
78.59
5.36
78.36
5.13
78.40
5.1'7
56
5
l0
55
I
55
I
55
I
55
I
55
I
54
55
56
57
58
.O'72
.022
.000
.025
>.01
<.01
.036
>.01
.028
>.01
.020
>.01
.021
>.01
.021
>.01
.950
.665
.952
.666
.950
.677
.949
.664
.950
.665
.950
.657
Nores: AGFI : adjustedgoodness-of-fit index; RMR : root-mean-squareresidual; CVD : cardiovasculardisease;Mspd : sensory-motorspeed;Pspd
= perceptual speed;RTspd = reaction time speed.
P38
EARLESAND SALTHOUSE
Table 6. InterconelationsAmong Age, Health, and Speed
Factor
Mspd
Pspd
RTspd
Health
CVD
Age
Mspd
.80
.62
Pspd
RTspd
.80
.54
.85
.81
11
-.41
_.43
.67
Health
-.3u
2 l
2f
-.19
,.16
-.o-1
.47
.t2
CVD
Age
-.43
-.43
.44
.33
-.54
, .61
-.64
.22
.40
.48
Nolcs. Standardizedcovariance estimatesof the linal nteasurement
rnodelfbr Sample I (abovediagonal)and Sample2 (below diagonal).CVD
= cardiovasculardisease:Mspd : sensory-motorspeedlPspd - perceptual speed:RTspd - reactiontime speed.
slowerspeedand lower self-ratedhealth,and thatthe speed
measures
havehigh positivecorrelations
with eachother.
StructurulModel
The basichypotheses
to be testedwerethatthereis a direct
eff'ectof age on self'-assessed
health,and that healththen
influencessensory-motorspeed,which in turn influences
perceptual
speed.Directeffectsof agewerealsoexpectedon
a l l t h r e es p e e dm e a s u r e sT.h i s s t r u c t u r ar ln o d e (l i . e . , S l ) i s
shownin Figure4. The variances
of the f'actorsas well as of
the indicatorswere estimatedby the model. Two covariancesbetweenfactorswere also estimated(i.e., sensoryrnotorspeedwith reactiontime speed,and perceptual
speed
with reactiontime speed).All other covariancesbetween
fackrrs and between indicators were tixed at zero. The
loadingof one indicatorof eachf'actorwas fixedat one ( i.e.,
Digit Copy, PatternComparison,Digit Symbol,and Health
Rating 2). It can be seenin Table 5 that the model had a
satistactoryfit, and did not differ significantlyfiom the
measurement
model(i.e., M2). The additionof a directpath
from healthto perceptualspeed(i.e., 52) did not significantly improvethe tit of the model.The basicmodel (i.e.,
S l ) l i t s i g n i f i c a n t lbye t t e rt h a nd i d a n u l l m o d e l( i . e . , N I ) i n
which all pathsbetweenlatentconstructs
werefixedat zero.
-['he
Figure4.
structuralntodcl. Paramcterslirr SarnpleI arc on the leli.
a n d t h o s el i r r S a n r p l c2 a r eo n t h e r i - u hitn p a r e n t h e s e P
s .a t hc o e l l i c i e n t a
s re
l r o m L I S R L , L ' sc o n l p l e t o l ys t a n d a r d i z esdo l u t i o n .A l l p a t h sa r e s i g n i f i c a n t
a t I < . 0 1 c x c c p tl i r r t h e p a t h sl i o m a g et o h e a l t ha n d h e a l t ht 0 R 1 ' s p dl i r r
S a n r p l e2 . w h i c h a r es i g n i t i c a nat t 2 < . 0 5 .
-->
?4(4s,
0s (.29)
A-)
Age
N6
(-so)
\,r,or, \
|
l-.se \r-.2
-")
/-'e
2 7\ ' 1
Additi on tl Cardiovascular D i sease
I
.78l.7s
RTspd
Measurementmodel.- The cardiovascular
diseasefactor
wasthenaddedto the model.This is a weakconstructin the
currentprojectbecauseit wasassessed
with two dichotomous
variablesin which the numberof non-zerovalueswas small
(i.e., l2 for surgeryand 69 for medicaltreatment).
Furthermore, the surgerymeasuredid not load significantlyon the
cardiovasculardiseasefactor. Nevertheless.the intercorre(i.e., M3 in Table 5) had a satisfactory
latedfactor-structure
fit, as did the factorstructureincludrngage(i.e., M4).
Structural model. - The basic cardiovasculardisease
m o d e l( i . e . ,5 3 ) i s s i m i l a rt o t h eb a s i ch e a l t hm o d e l( i . e . ,S l )
and is illustratedin Figure 5. The only differencefrom the
basic healthmodel (i.e., Sl) is that the effectsof age on
healthand the effectsofhealth on speedare hypothesizedto
be mediatedby cardiovascular
disease.As can be seenin
Table 5, this model fit the datawell. It is not significantly
worsethanthe measurement
model(i.e., M4), and it is sig-
ogtr
95(.93
Dr9tr
:.46 (-.22)
surecry{
CVD
vcos
4
49 (.44)
H.Cth R.t. 2
Adth
Umit
Figure5. The structuralmodel includingcardiovascular
disease.Parameters lbr Sample I are on the left. and thosefbr Sample2 are on the right in
parentheses.
All paths are significantat p < .01 except fbr the loading of
surgeryon CVD. the pathfrom ageto Mspd. andthe covarianceof Mspd and
RTspd for Sample I . The path from ageto Mspd is significantat p < .05.
AGE, HEALTH.ANDSPEED
nificantlybetterthan a null model (i.e., N2) in which all
pathsbetweenlatentconstructswere fixed at zero. The only
path that was not signilicant was the covariancebetween
sensory-motorspeedand reactiontime speed.Furthermore,
the pathfrom ageto sensory-motorspeedwas significantatp
< . 0 5 b u t n o t a tp ( . 0 1
The additionof a directpathfrom ageto health(i.e., 54 in
Table 5) did not significantlyimprovethe fit of the model.
The additionof direct pathsfrom healthto the speedfactors
(i.e., 55, 56, and 57) alsodid not significantlyimprovethe
model.Finally, a directpathfiom cardiovascular
diseaseto
perceptualspeed(i.e., S8) did not significantlyimprovethe
model. It can thereforebe concludedthat the model portrayed in Figure 5 cannot be substantiallyimproved by the
additionof omittedpaths.
Cross-Validation
Followingthe recommendations
of Breckler(1990), the
resultsof Sample I were cross-validated
using Sample2.
The samesequenceof model modificationsusedfbr Sample
I was usedto testthe modelsfirr Sample2, with the results
s u m m a r i z e idn T a b l e7 . T h e b a s i ch e a l t hm o d e l( i . e . . S l )
and the basiccardiovascular
diseasemodel(i.e., 53) fit the
data well. As with Samplel, no additionsto eithermodel
significantlyimprovedthe fit of the model.
Examinationof the coeflicientsin Figures4 and 5 reveals
that the patternof relationswas quite similar in the two
samples.The strengthof someof the relationsvariedacross
P39
samples(e.g., Sensory-MotorSpeedwith ReactionTime
Speed, PerceptualSpeed with ReactionTime Speed, and
Age with Health),but the discrepancies
arequiteminor.
Reg,ressktn
Analyses
An additionalanalyticalmethodwas usedto confirmthe
inferencesabout the relative influence of health on agerelateddifferencesin speed.The methodconsistedof using
hierarchicalmultipleregression
equationsto determinethe
proportionof age-relatedvariancein the composite(average
of z-scores)speedmeasurebefore and afier control of the
composite(averageof z-scores)healthindex.The variance
estimatesfor the compositesensory-motor
speedindex before and afier control o1'the compositehealth index were
. 2 2 1a n d . l 6 8 r e s p e c t i v e fl yo r S a m p l eI , a n d . 2 4 5 a n d. 2 2 2
respectively
for Sample2, whichcorrespond
to reductions
of
26.6Vcin Sample I and 9.4c/oin Sample2. Comparable
valuesfbr the compositeperceptualspeedindex were .326
a n d . 2 7 2i n S a m p l el , a n d . 2 9 3a n d . 2 1 6i n S a m p l e2 , t b r
reductionsof 16.6o/c
Valuesfbr the
and 5.tlolc,respectively.
compositereactiontime speedindex were .302 befbrecontrol of healthand .250 after controlof healthin Samplel,
and .294 and .270 betbre and afier control ol' health in
Sarnple2, which correspondto reductionsof 11.24/oand
8.27c, respectively.It is apparentfiom theseresultsthat
between l3o/c and 94o/cof the age-relatedvariance in the
compositespeedmeasureswas independent
of the health
measures.
Table7. Summaryof Model Fittinglbr Sample2
Description
dt
/)- va I ue
AGt-t
RMR
MI
M2
NI
I n l e r c ( ) r r e l a l el rdc t ( ) r\ t r u c l u r (
A d d i t i o no f a g e
Null model
59.62
65.62
669.02
79
35
4-5
00I
.001
.000
.943
.944
.572
.50u
.u63
l rJ.20
SI
Basic model (seeFigure4)
Corrpare to M2
Compareto N I
Add direct path fiom Health to Pspd
Conrpareto S I
65.97
.35
603.05
65.62
.35
-1t)
.002
>.01
<.01
.001
>.01
.94-5
.ttTtt
I
9
35
I
.941
.u63
S2
Alier Addition of CardiovascularDiseaseFactor
ti0.3u
M3
M4
N2
lntercorrelatedlactor structure
Addition ol'age
Null model
89.U4
113.10
44
5l
66
.001
.00r
.000
942
939
590
..12ti
. 75 9
15.5t
S3
B a s i cm o d e l( s e eF i g u r e5 )
Compareto M4
Compareto N2
Add direct path liom Age to Health
Compareto 53
Add direct path from Health to Mspd
Compareto 53
Add direct path from Health to Pspd
Compareto 53
Add direct path from Health to RTspd
Compareto 53
Add direct path fiom CVD to Pspd
Compareto 53
95.97
6 .r 3
677.73
91.64
4.33
94.7t)
t.2l
95.72
.25
9 5. 7 1
.26
95.91
.03
56
-5
l0
5-5
I
55
I
55
I
55
I
55
I
.00|
>.01
<.01
.001
>.01
.001
>.01
.001
>.01
.001
>.01
.001
>.01
910
.{339
942
.824
940
.173
940
.833
939
.845
939
.840
S4
S5
S6
S7
S8
Notes..CVD = cardiovasculardisease:Mspd = sensory-motorspeed;Pspd : perceptualspeed:RTspd : reactiontime speed
P40
EARLESANDSALTHOUSE
DlscussroN
Both healthandspeedwerefound to vary with age,but the
age-speedrelationswere only weakly mediatedby health.
This is consistent
with the resultsof Salthouse
et al. ( 1990).
who found only weak mediationby healthof age-cognition
relations.Evenwith a very basicability (i.e., the speedwith
which elementaryoperationscan be executed),therefore,
healthdoesnot accountfor a largeamountof the age-related
variancein performance.Although healthdid havea moderate effect on sensory-motorspeed,all of the effectsof selfratedhealthon perceptualspeedwere indirect and mediated
throughsensory-motorspeed.
Becausesubstantialdirect effects of age on speedwere
evidentin additronto the effectsmediatedby healthstatus,it
can be concludedthat factors other than self-ratedhealth
statusare responsiblefor much of age-relatedslowing in
relativelyhealthyadults.It is possiblethat,as Birren(1965;
Birren, Woods, & Williams, 1979) has suggested,agerelatedslowingis a manifestation
of primary aging, and is
relativelyindependent
of disease.The relationsthatdo exist
betweenself-assessed
health statusand measuresof speed
could:(a) reflectweakcausalinfluences
of healthon speed;
(b) be a consequence
of a common influenceof biological
statuson both setsof variables,or (c) represent
an effectof
basingthe ratingof one'shealthat leastpartiallyon assessmentsof one'sspeedof perfbrmance.
Obviously,additional
researchis neededto distinguishamongthesealternatives.
An important featureof the current project was that (as
recommended
by Breckler, 1990)the model modification
procedurewas cross-validated
in an independent
sampleto
decrease
the likelihoodofcapitalizationon chance.Because
the samepatternof resultswas evident in two moderately
large samples,the reportedrelationsappearquite robust.
The hypothesized
modelfit thedataadequately,
andtheonly
significantproblemoccurredwhen the cardiovascular
diseaseconstructwas addedto the model. This constructwas
weak in the current project becausef'ew subjectsreported
cardiovascular
problems,and the indicatorsdid not load
highly on the factor.
There are severallimitationsconcerningthe mannerin
which healthwas evaluatedin this project.First, one can
questionthe validity of self-reportedhealth status as a
measureof objectivehealth.However, it shouldbe noted
that self-ratedhealth has been found to relate to physician
(LaRue,Bank,Jarvik,& Hetland,1979),numassessments
ber of prescriptionmedications(Salthouse,Kausler, &
Saults,1990),andlongevity(Botwinick,West,& Storandt,
1978; see page 59 in Salthouse(1991) for more relevant
citations).Thus,althoughself-ratings
providea muchcruder
evaluationof healthstatusthan do physicianassessments,
they are relatedto more objectivemeasuresof healthstatus.
Second,an attemptwas madeto recruit only healthyvolunteers, and hence the range of health was undoubtedlyrestrictedrelativeto the generalpopulation.Thus the resultsof
the current study can only be generalizedto the relatively
healthy adult population.Nevertheless,becausesignificant
negativeage relationswere found with both the health and
speedmeasures,an opportunitydid exist for at least some
mediationalinfluence.
Although the results with the cardiovascularconstruct
must be consideredtentativebecauseof weak assessment
of
this construct, cardiovascularstatusmay be an important
factorin the negativerelationsbetweenageand self-reported
health status,and betweenself-reportedhealth and speed.
Previousresearchsuggestedthat cardiovasculardiseasewas
relatedto both perceptualspeed(Speith, 1964)and higher
cognitivefunctioning(Hultschet al., 1993).In the current
study, almost all of the effects of health on sensory-motor
speedwere mediatedby cardiovasculardisease,suggesting
that cardiovasculardiseasemay be the aspectof healththat
contributesto the negativerelationsbetweenage and speed.
This interpretation,however,needsto be investigatedmore
directly with more sensitiveandobjectivemeasuresof health
and cardiovascularstatus before it can be acceptedwith
confidence.
In summary,self-ratedhealthand speedwere both negatively relatedto increasedage. However, healthonly partially mediatedthe age-relatedvariationin speed,and much of
the relationthat did exist betweenhealthand speedappears
to have been mediatedby cardiovascularstatus.The major
conclusionfrom theseanalysesis that,within this relatively
healthysampleof adults,healthstatuswas associated
with
only a relativelysmall portion of the age-relatedvariancein
speed.Additional mechanismsmust thereforebe identified
to accountfor much of the nesativerelationsbetweenase
and speed.
AcKNowt-EDcMENTs
This researchwas supportedby NIA grant (R37 AGO6826) to Timothy
A. Salthouse.Julie Earles was supportedby an lnstitutional Research
Training Crant (T32-AG00I 75) to the Schoolof Psychologyat The Georgia
lnstituteof Technology.
Address conespondenceto Dr. Julie L, Earles, Departmentof Psyc h o l o g y , F u r m a n U n i v e r s i t y , 3 3 0 0 P o i n s e t tH i g h w a y , G r e e n v i l l e .S C
296 | 3-0999.
REFERENCES
B i r r e n , J . E . ( 1 9 6 5 ) .A g e c h a n g e si n s p e e do f b e h a v i o r :I t s c e n t r a ln a t u r e
a n d p h y s i o l o g i c acl o r r e l a t e sl.n A . T . W e l f b r d & J . E . B i n e n ( E d s . ) ,
(pp. 19l-216\. Springlield.
Behuvior, aging, and the nervouss_t.rle,rl
l L : C h a r l e sC T h o m a s .
B i r r e n ,J . E . , W o o d s ,A . M . , & W i l l i a m s ,M . V . ( I 9 7 9 ) .S p e e do f b e h a v i o r
as an indicatorofagechangesand the integrityofthe nervoussystem.ln
F . H o i f m e i s t e&
r C . M u l l e r ( E d s . ) ,B r a i n J u t t t r i o na n d o l d a g e ( p p . l 0 44). New York: Springer-Verlag.
B o l l e r ,F . , V r t u n s k i ,P . 8 . , M a c k . J . L . , & K i m , Y . ( 1 9 7 7 ) .N e u r o p s y chologicaf correlates of hypertension.Art'hives oJ Neurologt', 34,
70 I -705 .
B o t w i n i c k ,J . , W e s t , R . , & S t o r a n d t ,M . ( 1 9 7 8 ) .P r e d i c t i n gd e a t hf r o m
. Journal of Gerontology, 33, 755-762.
behavioraftest performance
Breckler, S. J. (1990). Applicationsof covarianceslructuremodeling in
psychology:Causefor concern?Ps ,-t'hologit'al
Bulletin, 107, 260-2'73.
Dawber, T. R. (1980). The FraminghamStadr'.Cambridge,MA: Harvard
University Press.
E l i a s ,M . F . , R o b b i n s ,M . A . , S c h u l t z ,N . R . , & P i e r c e ,T . W . ( 1 9 9 0 ) .I s
blood pressurean important variable in researchon aging and neuropsychological test performance? Journal of Gerontology: Psychological
S c i e n c e s4. J . P l 2 8 - P 1 3 5
, . B . , C o b b ,J . , & W h i t e ,L . R .
E l i a s ,M . F . , W o l f , P . A . , D ' A g o s t i n o R
(1993). Untreatedblood pressurelevel is inverselyrelatedto cognitive
functioning:The Framinghamstudy. AmericanJournal of Epidemiolo91,, 138' 353-364.
F a r m e r ,M . 8 . , K i t t n e r ,S . J . , A b b o t t ,R . D . , W o l z . M . M . , W o l f , P . A . , &
White, L. R. (1990). Longitudinally measuredblood pressure,antihy-
P40
EARLESANDSALTHOUSE
Dtscusston
Both healthand speedwerefound to vary with age,but the
age-speedrelationswere only weakly mediatedby health.
This is consistent
with the resultsof Salthouse
et al. ( 1990).
who found only weak mediationby healthof age-cognition
relations.Evenwith a very basicability (i.e., the speedwith
which elementaryoperationscan be executed),therefore,
healthdoesnot accountfor a largeamountof the age-related
variancein performance.Although healthdid havea moderate effect on sensory-motorspeed,all of the effectsof selfratedhealthon perceptualspeedwere indirect and mediated
throughsensory-motorspeed.
Becausesubstantialdirect effects of age on speedwere
evidentin additionto the effectsmediatedby healthstatus,it
can be concludedthat factors other than self-ratedhealth
statusare responsiblefor much of age-relatedslowing in
relativelyhealthyadults.It is possiblethat, as Binen ( 1965;
Birren, Woods, & Williams, 1979) has suggested,agerelatedslowingis a manifestation
of primaryaging, and is
relativelyindependent
ofdisease.The relationsthatdo exist
betweenself-assessed
healthstatusand measuresof speed
could:(a) reflectweak causalinfluencesof healthon speed;
(b) be a consequence
of a common influenceof biological
statuson both setsof variables.or (c) representan effect of
basingthe ratingof one'shealthat leastpartiallyon assessmentsof one'sspeedof perfbrmance.
Obviously,additional
researchis neededto distinguishamongthesealternatives.
An important f'eatureof the cunent project was that (as
recommendedby Breckler, 1990)the model modification
procedurewas cross-validated
in an independent
sampleto
decrease
the likelihoodofcapitalizationon chance.Because
the samepatternof resultswas evidentin two moderately
large samples,the reportedrelationsappearquite robust.
The hypothesized
modelfit thedataadequately,
andtheonly
significantproblemoccurredwhen the cardiovascular
diseaseconstructwas addedto the model. This constructwas
weak in the current project becausefew subjectsreported
cardiovascularproblems, and the indicators did not load
highly on the f'actor.
There are severallimitationsconcerningthe mannerin
which healthwas evaluatedin this project.First, one can
questionthe validity of self-reportedhealth status as a
measureof objectivehealth.However, it shouldbe noted
that self-ratedhealth has been found to relate to physician
(LaRue,Bank,Jarvik,& Hetland,1979),numassessments
ber of prescriptionmedications(Salthouse,Kausler, &
Saults,1990),andlongevity(Botwinick,West, & Storandt,
1978; see page 59 in Salthouse(1991) for more relevant
citations).Thus,althoughself-ratings
providea muchcruder
evaluationof healthstatusthan do physicianassessments,
they are relatedto more objectivemeasuresof healthstatus.
Second,an attemptwas madeto recruitonly healthyvolunteers, and hence the range of health was undoubtedlyrestrictedrelativeto the generalpopulation.Thus the resultsof
the current study can only be generalizedto the relatively
healthy adult population.Nevertheless,becausesignificant
negativeage relationswere found with both the health and
speedmeasures,an opportunitydid exist for at least some
mediationalinfluence.
Althoush the results with the cardiovascularconstruct
must be consideredtentativebecauseof weak assessment
of
this construct, cardiovascularstatusmay be an important
factor in the negativerelationsbetweenageand self-reported
health status,and betweenself-reportedhealth and speed.
Previousresearchsuggestedthat cardiovasculardiseasewas
relatedto both perceptualspeed(Speith, 1964) and higher
cognitivefunctioning(Hultschet al., 1993).In the current
study, almost all of the effects of health on sensory-motor
speedwere mediatedby cardiovasculardisease,suggesting
that cardiovasculardiseasemay be the aspectof healththat
contributesto the negativerelationsbetweenageand speed.
This interpretation,however,needsto be investigatedmore
directly with more sensitiveandobjectivemeasuresof health
and cardiovascularstatus before it can be acceptedwith
confidence.
In summary,self-ratedhealthand speedwere both negatively relatedto increasedage. However, healthonly partially mediatedthe age-relatedvariationin speed,and much of
the relationthat did exist betweenhealthand speedappears
to have been mediatedby cardiovascularstatus.The major
conclusionfrom theseanalysesis that,within this relatively
healthysampleof adults,healthstatuswas associated
with
only a relativelysmallportionof the age-related
variancein
speed.Additional mechanismsmust thereforebe identified
to accountfor much of the neeativerelationsbetweenage
and speed.
AcKNowLEDCMt
NTS
This researchwas supportedby NIA grant (R37 AGO6826) b Timothy
A. Salthouse.Julie Earles was supportedby an lnstitutional Research
Training Grant (T32-AG00| 75) to the Schoolof Psychologyat The Georgia
Instituteof Technology.
Address correspondenceto Dr. Julie L. Earles, Departmentof Psyc h o l o g y , F u r m a n U n i v e r s i t y , 3 3 0 0 P o i n s e t tH i g h w a y , G r e e n v i l l e ,S C
296 | 3-0999.
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B i n e n ,J . 8 . , W o o d s ,A . M . , & W i l l i a m s M
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70l -705.
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, . 8 . , C o b b ,J . , & W h i t e ,L . R .
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White, L. R. (1990). Longitudinallymeasuredblood pressure,antihy-
AGE, HEALTH, ANDSPEED
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ReceivedJanuttn 1l, 1994
Ac<eptedMa-t 25, 1994