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8
FunctionalAssessmentinSpinalCord
Injury
MarcelP.J.M.DijkersandJeanneM.Zanca
INTRODUCTION
Chronicdiseaseandinjuryoftenresult indifficultiesin performingday-to-day
activities because of physical, cognitive, or emotional impairments. In
rehabilitationclinicalpracticeandresearch,theprocessofdeterminingthetype
and degree of such problems, or theability toperformnormal acts, activities,
androlesistypicallydesignated“functionalassessment”(FA).TheaimofFAis
to measure the degree a person’s functioning deviates from “normal,” where
normalmay refer to typicalfunctioningfor persons without disabilities(either
all persons, or persons of the same age, gender, education, etc.), or deviation
fromtheperson’sownpreinjurystatus.“Assessment”inFArefersmostoftento
quantification, where the position of the person on a continuum ranging from
unable(completelackoffunction)toveryable(onalevelwithorevenbetter
than“average”orpreinjury)isdeterminedandexpressedinanumber.However,
the term “assessment” also has a second meaning, referring to evaluation or
valuation: establishing the worth or meaning attached to the (amount of)
function by the person involved or by others. Although the two types of
“assessment” are strongly connected, they are not synonymous. Whereas it is
generallytruethatmoreableisconsidered“better”or“morevaluable,”people
may differ in how they value one ability compared to another (walking vs.
bathing), and in how they value one specific level of an ability compared to
anotherlevel(1). In thischapter,wegive readersanoverview oftheconcepts
and techniques useful in evaluating FA instruments (also called scales or
measures) and of the issues involved in selecting instruments for clinical and
research applications in spinal cord injury (SCI). An overview of available
measuresisprovided,asarereferencestosystematicreviews(SRs)thatdiscuss
thevariousavailableFAmeasuresindetail.
THEDISABLEMENTCONTINUUM
“Functioning” may cover an extremely broad area, from simple functions
involving a single organ system to complex activities that are dependent on
multiplephysicalandcognitiveskillsandareimplementedinsocialinteractions
that follow established social and cultural patterns. The World Health
Organization’s (WHO) International Classification of Functioning, Disability,
and Health (ICF) (2) (Figure 8.1) is a useful framework to place various
conceptsandtermsencounteredintheFAliterature.
TheWHOdefinesImpairmentas“problemsinbodyfunctionorstructureas
asignificantdeviationorloss,”includingdeficitsinphysicalorpsychological
functions(2)(p.12).ThepositiveaspectisBodyfunctions,whicharedefinedas
the physiological functions of body systems. In SCI, key measures of
impairmentincludethemotorandsensoryscoresoftheInternationalStandards
forNeurologicalClassificationofSpinalCordInjury(ISNCSCI)(3).
Attheleveloftheperson,ActivityischaracterizedintheICFas“execution
of a task or action by an individual” (2) (p. 14). Its negative aspect, Activity
limitations, is defined as “difficulties an individual may have in executing
activities” (2) (p. 14). In rehabilitation, the prototypical measure of activity
limitationshasbeentheFunctionalIndependenceMeasure(FIM)(4),butmany
other instruments have been used; in the SCI field, the Spinal Cord
IndependenceMeasure(SCIM)(5)isemployedincreasingly,especiallyoutside
theUnitedStates.
Finally, the person in interaction with others may have Participation
restrictions, which are defined as “problems an individual may experience in
involvementinlifesituations”(2)(p.14);thepositivecounterpart,Participation,
is characterized as “involvement in a life situation”(2) (p. 14). In the SCI
literature,theCraigHospitalAssessmentandReportingTechnique(CHART)(6)
isoftenusedasameasureofparticipationrestrictions.
ManytermsdevelopedpriortooroutsidetheICFcanbeplacedonthesame
disablement continuum, as shown in Figure 8.1. The core interests of
rehabilitation,activities ofdaily living(ADLs)(sometimes designatedbasicor
personal ADLs) coincide with Activities. Extended (instrumental, advanced)
ADLs (IADLs) are generally defined to straddle the Activity-Participation
border; on the other side of the continuum, functional limitations typically
represent activities such as grasping and lifting that cross the divide between
ImpairmentsandActivities(7).Communityintegration(inolderliteratureoften
calledhandicap)assessmentsmayquantifyaspectsofIADLs,andotherfacetsof
Participation, with emphasis on the social interactional components. Health
status,atermusedbyhealthservicesresearchers,typicallyisoperationalizedas
combining elements of Impairment and Activity Limitations, although some
measures, such as the well-known Short Form-36 (SF-36) (8), also include
indicatorsofParticipation.TheSF-36isnowincreasinglyusedasameasureof
qualityoflife(QOL).QOLhasbeendefinedinmanyways(9);mostdefinitions
ofhealth-related QOL(HRQOL) overlapwithActivities and Participationand
may even take in some aspects of Impairment. “Disability” may refer to
Impairments, Activity limitations or Participation restrictions, or an
amalgamation of these three. “Disablement” is sometimes used in place of
“disability” or may refer to the process by which various factors lead to
disability.
FIGURE8.1Thecontinuumoffunctionalassessment.
ADLs,activitiesofdailyliving.
THESTRUCTUREOFFUNCTIONAL
ASSESSMENTINSTRUMENTS
Atthesimplestlevel,FAmeasuresconsistofanumberofseparateitems,each
oneofwhichreferstoanarroworbroadability,skill,oractivity–forinstance,
liftingoverhead,transferringintoabathtub,ormakingtelephonecalls.Oneach
item,anywherefromtwotoseven, distinctlevelsor categoriesof“ability” are
distinguished.Thelowestcategorytypicallycorrespondstonoability/cannotdo
atall/needsmaximumhelp,andthehighesttoindependence,“normal,”oreven
above-average skill. Additional metrics have been used, such as difficulty
experienced and time needed. For measures of participation, metrics used
includefrequencyofperforminganactivity,hoursspentonanactivity,shareof
activities performed, and others (10). The numbers (item scores) a patient or
subject receives on the constituent items typically are added together,and the
total (with or without further arithmetical manipulation) reflects his or her
functionalstatusinthedomainbeingmeasured.
Forsomemeasures,theitemsallhavethesamenumberofcategories(steps)
and the same minimum and maximum value (e.g., FIM), but that is not
necessarilythecase—forinstance,theBarthelIndex(11)consistsofsomeitems
thathaveonlytwocategoriesofability,butotheritemshavethree.Differential
scoringof thecategories fromoneitem tothenext canbe usedtoexpress the
relative weight (importance) of the constituent skills for overall functioning,
accordingtotheinstrument’screator.Aseparateweightingsteppriortoaddition
canbeusedtoachievethesamepurpose.
Someaspectsoffunctioningcanbemeasureddirectly,suchastherangeof
motion(indegrees)ofajoint,orthespeedwithwhichonewalksamile.These
measurementsaremadeusingaratioscale,inwhichthereisa truezeropoint
(onecanhavenojointmotionornospeed)andequidistancebetweenthepoints
on the scale. Such measures allow us to calculate arithmetically meaningful
meansforagroup, or percentage improvement over time. However,for many
measures,the numeric valuesofthe categories (item scalecategoriesor steps)
represent measurement on an ordinal scale—they only indicate relative order
along the fully able/not able (or not participating at all/fully participating)
continuum, but the differences between scale steps are not necessarily
equivalent, and the values chosen for the categories themselves are arbitrary.
Consequently, adding up the scores for the items to obtain the total score is,
strictlyspeaking,notalegitimatemathematicaloperation.Therefore,totalscores
on ordinal measures do not reflect the subject’s/patient’s position along a
continuumthathasatruezeropoint,anddistancesbetweenscalepointsdonot
necessarilycorrespondtotheabilitydifferencesthatexistinreality.Forinstance,
the difference between the FIM motor subscale scores of 20 and 40 is not
necessarilythesameasthedifferencebetweenscoresof40and60.Oneshould
becarefulininterpretingFAinstrumentscoresasreportedforindividualsandfor
groups. In particular, “percent improvement” and “change efficiency scores”
shouldbeconsideredasnothing butcrudeapproximationsofthemathematical
precision they appear to offer. However, research has shown that if the item
categoryvaluesarechosen“reasonably,” thesum ofordinal itemscorresponds
quitewellto valueson atrueratioscale,at leastfor intermediatelevelsofthe
continuumof total scores. Rasch analysis, a mathematical procedure based on
Item Response Theory (IRT), has been used to transform a set of scores on
ordinal FA items into a score on an interval scale (12,13). The theoretical
assumptions and mathematical manipulations underlying Rasch analysis-based
FAinstrumentsarebeyond thescope ofthischapter;goodintroductionstothe
techniqueanditsapplicationtoFAmaybefoundinBondandFox(14).
ISSUESINFUNCTIONALASSESSMENT
FAinstruments seem simple to create and apply,and their apparent simplicity
hasledtothedevelopmentsofhundredsofmeasures,manyofwhichhavenever
seen more than one application. Several issues need to be considered in their
creationandapplication,manyofwhicharelinkedtooneanother.Amongsome
importantconcernsarethefollowing:
CapacityandPerformance
Two aspects of functioning are commonly distinguished: capacity and
performance.(2,15)Capacityiswhatpeoplecandounderoptimalcircumstances
—well rested, encouraged to do their best, in an environment with minimal
barriers.Performanceiswhattheyactuallydoineverydaylife.PeoplewithSCI
whocandoself-caremaynotalwaysdoit,foravarietyofreasons.Differences
betweenone’sperformanceandcapacitymaybeduetoseveralfactors,among
whicharepersonalprioritiesandchoices.Forexample,studieshaveshownthat
many for whom self-care is a “marginal” skill prefer to have a personal care
attendantorfamilymemberperformtheircare,sothattheycaninsteadusetheir
time and energy for what they consider to be more important—for instance,
gettingoutofthehouseandtotheirjob.Anotherkeyfactoristheenvironment,
which(initsbroadest sense) consists of such characteristics as social support,
attitudes,physicalfeatures,andaccesstotechnology.Itiswidelyrecognizedthat
functioning results from an interaction of one’s intrinsic ability and
environmental characteristics, but further study is required to understand the
specificnatureandstrengthofsuchinteractions(16).
AttheImpairmentendofthedisablementcontinuum,measuresoffunctional
limitationstend tobecapacity focused.The ASIAmotorscale isbasedon the
ability to contract the key muscles, and the physician and patient are hardly
interestedinthepatient’sactualfrequencyofcontractingthosemusclesover24
hours. At the other end of the continuum, measures of Participationquantify
performance.Itiseitherimpossibletotestcapacity(howcouldonetest“ability
tofunctionasabrainsurgeon,”)ornotofconcern:itisactualperformancethat
isofinterestwhenevaluatingthelong-termoutcomeofrehabilitativeefforts,not
potential.Itisinthemiddleground,thedomainofActivities,thatadiscrepancy
between capacity and performance is most likely to be relevant, and where
performance is modifiable with environmental and other interventions (15).
Depending on one’s definition of “environment,” assistive technology (AT) is
eitherpartofit,oryetanotherfactorthatisnotpartofanindividual’sphysical,
cognitive, and emotional characteristics, but interacts with the latter to affect
functioning.TheuseofATisakeyissueinFA.Whetheronewantstoquantify
capacity or performance, it should be specified whether AT was used by the
person during the assessment. The rehabilitation field has not developed a
consistent approach to this (17) with some FA measures ignoring the use (or
nonuse)ofAT,othersexplicitlyincludingorexcludingATacrosstheboard,and
yetothersbeinginconsistentfromoneitemtothenext.Ifonewantstoevaluate
the effect of natural recovery after SCI on function, measurement of skill
completionwithoutATpresumablywouldbemostappropriate.However,ifthe
interestisinlevelofindependence,assessingcapacityorperformancewiththe
ATthepersonusuallyemploysmaybethebestapproach.Todate,theSCI-FIis
theonlyFAmeasurespecifictoSCIforwhichversionswith(18,19)andwithout
(12,13,20)theuseofAThavebeendeveloped.
Testing,Observing,andReportingonPerformance
Threemainmethodsareusedtocollectfunctionalinformation.Testinginvolves
requiringthepatient orclient(orresearchsubject)toperform specifictasksor
skills under the direct supervision of a test administrator, who times the test,
assessestheamountofhelpfrom devicesoraidesthatisneeded,andso forth.
Thistendstooccurinlaboratoryorclinicalsettings,buttestingcanalsobedone
intheperson’shomeorotherlocalewheretheactivitiesinvolvedareorshould
beperformed.Dependingonthedegreetowhichthetestsituationapproximates
anoptimalone,theresultingscorequantifiesoptimalcapacity,orcapacityinthe
situation that is considered most relevant to the uses to which the functional
informationistobeput.
Observationofhabitualbehavioristhebasisforquantifyingwhattheperson
doesdo,ratherthanwhatheorshecando.MostassessmentsofActivityreported
aspartofinpatientoroutpatientrehabilitationprogramsareobservation-based—
at least in theory. For instance, the Uniform Data System for Medical
Rehabilitation(UDSMR)FIMadmissionanddischargescoresaretobebasedon
whatpatientsactuallydointhefirst3daysafterrehabilitationadmissionandthe
last 3 before discharge. In practice, there is continuous pressure on them to
perform at their best, especially in treatment by physical and occupational
therapists,andthemeasureofperformanceturnsintooneofcapacity.
AthirdwayofcollectingFAinformationisthroughreportbythepatientor
by proxy, such as a family member. These reports can involve capacity (for
instance,intheCapabilitiesofUpperExtremity[CUE]instrument[7]),butmore
typically address performance. Questions are asked about how the person
performsthevariousactivitiesinhisorherdailyroutinethatareincludedinthe
FAmeasure.Usingastandardizedquestionnaire,trainedinterviewerscanreacha
high level of inter-rater (inter-interviewer) reliability. This is how data are
typicallycollectedforfollow-upassessmentsintheUDSMRandotherprogram
evaluationsystems,aswellasinSCIModelSystemsresearch.
Allthreemethodshavetheiradvantagesanddisadvantages,intermsofcost,
needforexpertpersonnel,requiredabilityofthepatienttocooperatewithdata
collection,and soforth. Ifcapacitydataareof interest,testing isthe preferred
method. For true performance data, interviewing has typically been the most
feasiblemethodofassessment.However,smallsensorsthatcanbewornonthe
body or placed in environments where people live provide new ways of
observingbehaviorineverydaylife(seethesection“InstrumentedRecording”).
Problemsarisewhen the data obtained by two methods need to be linked.
Forinstance,atypicalquestion(clinicallyandinresearch)iswhethertheperson
with SCI manages to maintain or even improve on the skills he or she was
discharged with from inpatient rehabilitation. If between hospital and home a
differenceinfunctional performanceis noted,is thisdue tochange inthe data
collectionmethodperse,orduetothedifferentenvironment,orevenbecauseof
changesinthetrueunderlyingcapacity(resultingfromneurologicalrecovery)?
This issue has hardly been studied, and we do not know enough about how
scoresonagivenFAinstrumentmaydifferbydatacollectionmethodtotease
apartdifferencesinscores.
TheNatureoftheItemsinFAInstruments
InanIQtest,thepersontestedcompletesmultiplearithmeticproblems,logical
reasoningtests,andotheritemswhichinthemselvesarenotofinteresttothetest
administrator. The IQ score that results is of interest, because it gives an
(approximate)indicationoftheperson’soverallintelligence.Thefocusisonthe
underlying trait—intelligence. In FA, however, the items most likely have
intrinsicmeaningtothepersonperformingtheassessmentandtotheindividual
beingassessed:theyreflectactivitiesthatareofimportanceinandofthemselves
—whether it is stair climbing or communicating a simple idea. Because the
items(tasks,activities)are ofinterestinthemselves(aswellas intermsofthe
underlying construct they represent), there is a tendency to include in FA
measures the full panoply of acts that are part of normal human functioning.
Such an extensive menu may be feasible when various staff (speech therapy,
neuropsychology, etc.) report on patient status within their area of expertise
becausetheassessmentworkloadisdividedamongseveralpeople.Insituations
wheresubjectsaretestedorarerequiredtoreportontheirownperformance,the
inclusionofmanyitemsincreasesthephysicalandmentalburdenandmaycause
fatigue affecting the accuracy of assessment findings. Maintaining a balance
betweenfeasibilityandinclusionofallfunctionaltasksthatarekeytolivinghas
alwaysbeenaconcernforFAinstrumentdevelopers.
WhenthefocusofFAshiftsfromperformanceofspecificindividualtasksto
the status of broad underlying abilities (“self-care”; “motoric strength and
coordination”),the need toincludeevery possible itemdiminishes.Traditional
psychometric methods (see later) can be used to show that the underlying
constructcanbemeasuredwithonesetofitemsorindicators(say,A,F,andK)
aswellaswithanotherset(say,B,C,andL),andthattheresultingtotalscores
will have high correlations with one another. For instance, some measures of
functional limitations do not attempt to “cover the waterfront”—they select
activitiesthatarerepresentativeoftheentireuniverseofrelevantitemsanduse
those to score, for instance, upper extremity functioning. After all, once it is
knownhowmuchdifficultyasubjecthasinpickingupacanofsouporaream
of paper, it should be fairly clear how well she would do lifting a paperback
book.Computeradaptive testing(CAT),in whicha subsetofitemsrelevantto
thepersonbeingassessedispresentedinapredeterminedorder,hasthepotential
to balance the need to capture a full range of functional abilities with the
feasibility of assessment administration (see the section “Computer
administration”) (21,22). The extent to which this approach is appropriate for
Participationisunclear.IsParticipationasingleunidimensionalconstructorare
multipledimensionsortypesofconstructsrequiredtocharacterizeit?Theseand
other problems involved in measuring participation are discussed in greater
detailelsewhere(10,23).
ISSUESINMEASUREMENT:THEMETRIC
CHARACTERISTICSOFFAINSTRUMENTS
Wheneverwemeasure,errorcreepsintotheresultingscore,whetheritisasmall
errorinmeasuringsimpleconcretecharacteristics(forinstance,theweightofa
person), or a large error in quantifying abstract concepts such as
authoritarianism.FAisnoexception,andtheissueisnotsomuchgettingridof
theerror(weneverwillbeabletodothatcompletely),butbeingsensitivetothe
amountoferrorourdatamaycontainandbeingawarewhatthepresenceoferror
meansforanyconclusionswedrawandactionsweundertakebasedonthedata.
The developers and users of FA instruments have mostly relied on
methodologiesforinstrumentdevelopmentoriginatinginpsychology,knownas
psychometrics.Psychometricsisaverytechnicalandformostcliniciansavery
boringsubject,butknowledgeofsomeofthebasicsisnecessaryforthefruitful
use of FA instruments. Additional information may be found in handbooks in
thisarea (e.g., 24) and didactic articles (e.g., 25). The paper by Johnston and
GravesisnotonlyfocusedonSCI,butaddressessomeissuesinIRTapproaches
tomeasurementinstrumentdevelopmentthatarenottoucheduponhere(26).
Traditionally,two aspects ofthedatareflecting the resultsofmeasurement
havehadmostemphasis,validity,andreliability,butinclinicalapplicationssuch
issues as sensitivity and practicality are increasingly getting attention. In
psychometrictheory,reliabilityisanaspectofvalidity,butmostpeopletendto
thinkofthemasseparatecharacteristicsofinstruments(or,moreproperly,ofthe
dataproduced by instruments),and the techniquesforquantifying validityand
reliability are separate. “Validity” refers to the question: is this instrument
measuringwhatitpurportstomeasure?IfitistargetingcharacteristicX,dothe
numbers that result from the measurement operation (the “scores”) actually
reflect X, and not characteristic Y, or a little of X with a lot of trait Z?
“Reliability” refers to the question: how reproducible is this measurement—if
werepeatedthemeasurementoperationwiththesame“ruler,”andweknowthat
thepersonhasnotchanged,wouldwegettheexactsameresult?Asillustratedin
Figure8.2, an instrument can be very reliablewithout beingvalid. If itis not
reliable at all, it is by definition not valid. The goal we areaiming for is FA
instruments that are both reliable (they give results that arereproducible) and
valid(theymeasurewhatwewanttomeasure).
Over the years, a great many techniques have been developed to estimate
validity and reliability, each applicable to different situations. Unfortunately,
psychologistsandsocialscientistshavefallenintothehabitof“inventing”new
typesofvalidityandreliabilitybynamingthemafterthetechniques.However,
thereisnosuchthingastest–retestreliabilityorconstructvalidity.Thereisonly
one validity and one reliability for each instrument, which can be estimated
usingdifferenttechniques.
Reliability
Estimatingthereliabilityofmeasuresistheeasiesttounderstand.Allestimation
methodsarebasedonsomeformofrepeatmeasurement.Iftwocliniciansatthe
sametimeratetheabilityofpatientXontheFIMGroomingitem,theyshould
comeupwiththesamenumber—orelseoneorbotharewrong.Wecanestimate
the reliability of the FIM grooming item as used by these two clinicians by
havingthetworateafewhundredpatients,andcalculatehowoftentheyagree—
eithercompletelyagree,oralmostso. Astatisticalformulasuchas coefficient
kappa(orweightedkappa) can be used to express the level of agreement. All
these formulas are constructed in such a way that the result, the reliability
coefficient, varies between 0.00 (no reliability whatsoever) and 1.00 (perfect
reliability). “Inter-rater reliability” can be estimated based on a few raters to
representallpossibleraters,sothatwecanhaveanideaastohowreliablethis
one-iteminstrument(FIMGrooming)isinthehandsoftheaverageclinician.
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