setting up a cohort study on functioning

SwiSCI

INVITED REVIEW

Setting Up a Cohort Study onFunctioningDeciding What to Measure

ABSTRACT

Cieza A, Boldt C, Ballert CS, Eriks-Hoogland I, Bickenbach JE, Stucki G: Setting

up a cohort study on functioning: Deciding what to measure. Am J Phys Med

Rehabil 2011;90(suppl):S17YS28.

The objectives of this article were to (1) answer the question of what to measure

in a cohort study in which the main focus is the understanding of functioning over

time for a specific population and to (2) describe the process of determining what

to measure using a theory-informed selection of domains of functioning based

on the International Classification of Functioning, Disability and Health (ICF).

The Swiss Spinal Cord Injury Cohort Study, a cohort study being carried out in

Switzerland for a population of persons with spinal cord injury, was used as an

example. A set of domains for the Swiss Spinal Cord Injury Cohort Study was

identified demonstrating the application of the methodology. This set consisted of

45 categories of the ICF. Defining what to measure using the ICF is a valuable

technique for the cohort researcher because it guarantees comparability of data

and comprehensiveness of scope, enhancing the prospects of the study results

being understood and is consequently used by health professionals as well as in

other contexts, such as in health and social policy.

Key Words: Research Design, Epidemiology, Cohort Studies, ICF, Spinal Cord Injury

H ealth, for an individual or a population, is important not only for what itis but also for what it makes possible. Health Bbroadens fair opportunity;[1 it isa precondition for any plan, aspiration, or goal in life. When the health of anindividual or a population is compromised, what matters to them is at risk. Inspinal cord injury (SCI), for example, individuals will experience profound andfar-reaching changes in their heath that threaten to undermine nearly all as-pects of their life that define who they are as individuals. It is, therefore, essen-tial to understand this impact of ill health and respond in ways that ensure, asfar as possible, that this life disruption does not destroy what is important topeople and how they wish to live their lives.

Understanding Functioning and HealthUnderstanding all that health is and what its determinants are is one of

the main challenges for health researchers, clinicians, and health policymakers.

Authors:Alarcos Cieza, PhD, MPHChristine Boldt, MScCarolina S. Ballert, MScInge Eriks-Hoogland, MDJerome E. Bickenbach, PhD, LLBGerold Stucki, MD, MS

Affiliations:From the Swiss Paraplegic Research(SPF), Nottwil, Switzerland (AC, CB,CSB, IE-H, JEB, GS); ICF ResearchBranch in cooperation with the WHOCollaborating Centre for the Familyof International Classifications inGermany (at DIMDI), Nottwil,Switzerland (AC, JEB, GS); ResearchUnit for Biopsychosocial Health,Institute for Healthand Rehabilitation Sciences,Ludwig-Maximilians-University,Munich, Germany (AC); andDepartment of Health Sciencesand Health Policy, University ofLucerne and SPF, Nottwil,Switzerland (JEB, GS).

Correspondence:All correspondence and requests forreprints should be addressed to:Alarcos Cieza, PhD, MPH, Institute forHealth and Rehabilitation Sciences,Unit for Biopsychosocial Health,Ludwig-Maximilians-University,Marchioninistr. 17, 18377 Munich,Germany.

Disclosures:Financial disclosure statements havebeen obtained, and no conflicts ofinterest have been reported by theauthors or by any individuals in controlof the content of this article.

0894-9115/11/9011(Suppl)-0S17/0American Journal of PhysicalMedicine & RehabilitationCopyright * 2011 by LippincottWilliams & Wilkins

DOI: 10.1097/PHM.0b013e318230fddb

www.ajpmr.com Setting Up a Cohort Study on Functioning S17

Copyright © 2011 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.

Unless health is made concrete and operational,however, it cannot be measured or analyzed. Theconcept of functioning, as currently defined bythe World Health Organization, is the operation-alization of health that comprehensively captureswhat matters to people.2 Studies that aim to com-prehensively understand health and its impact onpeople’s lives, such as the example used in this pa-per, the Swiss Spinal Cord Injury Cohort Study(SwiSCI), therefore relies on functioning as a mean-ingful operationalization of health.

Functioning can be described in discrete cate-gories, such as memory, grasping, walking, self-care,and interpersonal relationships, and in terms of thesecategories, it can bemeasured. We knowmuch aboutfunctioning and problems with functioning; ourknowledge, however, is usually restricted to specificand isolated categories that are directly affected byadverse health conditions such as diseases, disorders,and injuries. In addition, we know relatively littleabout how functioning in persons with health con-ditions, such as SCI, changes over the life span. Ourknowledge is fragmentary, and we do not have acomprehensive understanding of how areas of func-tioning interact or affect each other.

The World Health Organization has taken thefirst step to address the challenge of a comprehen-sive understanding of functioning by developing aninternational descriptive classification in the Inter-national Classification of Functioning, Disability,and Health (ICF).3 The ICF is both a comprehen-sive conceptual model of functioning and a classi-fication of functioning and its determinants in theenvironment and in the person. The ICF model andclassification are comprehensive, not only becauseit accounts for the determinants of functioning butalso because it covers the full range of categories offunctioning, from body level functions and struc-tures to the categories of functioning at the personand societal levels as activities and participation.

The challenge of understanding changes infunctioning over time is methodologically addres-sed by longitudinal studies, and in the case of thestudy of functioning in a specified population suchas persons with SCI, a cohort study is the ideal de-sign. A cohort study is a longitudinal study of thesame group of people (the cohort) in time. Cohortstudies aim the description of relationships amongvariables, especially casual relationships.4

Theory-Informed Approach to PerformingCohort Studies Using the ICF

Cohort studies are resource- and cost-intensiveand have to be carefully planned so that only vari-

ables relevant to the main focus of interest aretaken into account and no relevant variables aremissed. When the cohort study focuses on func-tioning, from a comprehensive perspective, the ICFcan ensure that all potentially relevant variables aretaken into account. The use of the ICF avoids thepractice of selecting variables based on convenienceor other practical considerations, such as their usein available instruments, or based on tradition. Be-cause the ICF is built on a comprehensive model,it allows researchers to determine what to measurein a top-down, theory-informed manner. In addi-tion, the ICF contributes data comparability acrosspopulations and settings, which further adds to thevalue of cohort studies.

In the ICF, the determinants of functioning arethe health condition, personal factors, and environ-mental factors. Health conditions are classified inthe International Statistical Classification of Dis-eases and Related Health Problems, and the clas-sification of environmental factors is provided inthe ICF. How environmental factors can be incor-porated into cohort studies is discussed in an ad-junct paper.5 Personal factors, however, are notclassified in the ICF, but they can and should beincluded in a cohort study for a complete under-standing of functioning. Lacking a classification,a cohort study such as SwiSCI is challenged tocome up with its own proposal for capturing thepsychologic-personal perspective on functioningand disability, and that proposal is also presentedin an adjunct paper.6

Steps for Defining What to Measure in aCohort Study

The ICF categories are hierarchically arrangedin the classification, with increasing levels of spec-ificity. The chapter headings are the most general,for example b1 Mental functions, and the second-(b152 Emotional Functions), third- (b1521 Regu-lation of Emotion Functions), and in the case ofsome body functions and structures, fourth-levelcategories are increasingly more specific. At anyof these levels, however, for the purposes of deter-mining what to measure, it is always important toidentify particularly relevant aspects of these cate-gories to measure. To distinguish among levels ofspecificity, the relationship between levels in theICF, we will use the term category specificationto denote those aspects of ICF categories that areappropriate for the task of determining what tomeasure.

For example, researchers should decide whetherto assess an ICF category such as b152 Emotional

S18 Cieza et al. Am. J. Phys. Med. Rehabil. & Vol. 90, No. 1 (Suppl), November 2011


functions or an aspect of this category as a speci-fication relevant to the study, such as Bdepression[or Banxiety,[ neither of which is ICF an third-level term under b152. A category specification ofan ICF category must, at a minimum, be the samedimension of functioning as the category itself:only body structures can be specifications of bodystructures, only body functions can be specifica-tions of body functions, and so on. By the same rea-soning, only personal factors can be specifications ofpersonal factors, and only environmental factorscan be specifications of environmental factors. Forguidance, the operational definition of each ICFcategory can be used to select possible categoryspecifications because these definitions were de-signed to provide users of the ICF with sufficientguidance to apply on each ICF category. The task ofthe researcher is to decide at what level of detail heor she wishes to measure in the study and whichcategory specifications to use.

For this reason, two steps are required whendefining what to measure in a cohort study on func-tioning: first, determine which ICF categories haveto be addressed for a comprehensive understandingof functioning for the specific population, whichwill be called the domain set here and second, de-termine which category specifications of ICF cat-egories in the domain set need to be measured.

Objective and Specific AimsThe objective of this article, therefore, was to

describe the process of addressing the question ofwhat to measure in a cohort study in which themain focus is on the understanding of functioningin time for a specific population. The specific aimswere (1) to describe the process that establishes adomain set of ICF categories that determine whatto measure in a cohort study on functioning and (2)to describe an approach for selecting category spec-ifications for each ICF category in the domain setto be measured in the study.

In this paper, SwiSCI, a cohort study being car-ried out in Switzerland on a population of personswith spinal cord injury, will be used as a case inpoint to demonstrate the methodology.7

METHODS

Domain Set of What to MeasureThe process of selecting ICF categories that

make up the Domain Set of what to measure hasthe following steps: (1) use the ICF categories ofthe Minimal Generic Set as the starting point ordefault set, (2) identify and add the ICF categories

of the ICF Core Set applicable to the cohort studypopulation where available, and (3) determine andadd relevant factors from the psychologic-personalperspective.

Use of the ICF Categories of theMinimal Generic Set

To facilitate data comparability across studypopulations and time, a Minimal Generic Set ofICF categories has been developed (Cieza et al.,unpublished data, 2011). This minimal set containsthe smallest number of categories of functioningthat can explain significant differences betweenpeople with different levels of health. Its develop-ment was based on the eight functioning domainsthat were used in the World Health Survey con-ducted by the World Health Organization in theearly 2000’s and in a statistical analysis of popula-tion-based surveys. Any cohort study on function-ing can profitably use the Minimal Generic Set asits starting point.

The following ICF categories contained in thecurrent version of Minimal Generic Set5 are thestarting point of the domain set:

b130 Energy and drive functionsb152 Emotional functionsb280 Sensation of paind230 Carrying out daily routined450 Walkingd455 Moving aroundd850 Remunerative employment

Although the default is to include all of theseICF categories, in the case of d450 Walking andd455 Moving around, because both address relatedaspects of mobility, it might be preferable to selectone for the study population.

Identifying and Adding ICF Categoriesfrom Applicable ICF Core Sets

In addition to the generic approach guaran-teed by the Minimal Generic Set, ICF Core Sets havebeen developed across a range of the most bur-densome health conditions8 and settings. The ICFCore Sets are selections of ICF categories that cap-ture the essence of what is relevant to people withspecific health conditions or in determined health-care settings. The selection of categories for theICF Core Sets is based on evidence and an inter-national expert consensus process.9

For all of the 22 condition-specific ICF CoreSets developed to date, a brief and a comprehensiveICF Core Set has been created. The Brief ICF CoreSet is composed of the essential ICF categories that



should be taken into account for any patient withthe health condition or in any setting for which thecore set was developed. The Brief Core Set, or sim-ply the ICF Core Set, captures the essence of theexperience of persons with a specific health condi-tion or in a specific setting. It therefore serves asthe starting point for condition-specific researchand basic clinical documentation. The Comprehen-sive ICF Core Set serves as a reference pool of po-tentially relevant categories of functioning anddeterminants of functioning that can be drawnupon to describe specific issues of functioning inthe population under study. The ComprehensiveICF Core Set may also be used in multidisciplinaryrehabilitation programs.

The ICF Research Branch homepage(www.ICF-research-branch.org) provides a list ofavailable ICF Core Sets, and the researcher canconsult this list to determine which is applicableto the study population. The brief versions are thestarting point because the domain set should onlyinclude the essential ICF categories. However, ad-ditional categories from the comprehensive sets (orthe ICF as a whole if necessary) can always beconsidered and added to this set if required by thestudy objectives and study population. In generalterms, if the ICF categories from the brief ICF CoreSet were not already included in the Minimal Ge-neric Set, they are then added to the domain set.

Determining and Adding RelevantFactors from the Psychologic-PersonalPerspective

Finally, for the domain set of what to mea-sure, a selection of relevant factors that capturethe psychologic-personal perspective on function-ing and disability need to be added. Until the re-search has been done to determine the conceptualnature of the component of personal factors in thecontent model for ICF,10 two approaches can befollowed to identify classes of such factors as can-didates for inclusion in the domain set (Cieza et al.,unpublished data, 2011):

Secondary analyses of existing data sets of puta-tive psychologic-personal factors, such as theinformation collected within the scope of thedevelopment process of the ICF Core Sets inwhich information on psychologic factors fromthe patient’s perspective and from the healthprofessional perspective are available, and

A literature review combining a systematic searchof the health conditions in the cohort studyand the description of factors from the psy-

chologic-personal factors that are likely can-didates for the Personal Factor classificationin the ICF.

Selection of Category Specifications ofWhat to Measure

The approach recommended for selecting cat-egory specifications for the domain set is basedon an evidence-based process including literaturesearch described in detail in the section ‘‘ElectronicLiterature Search.’’ The aim was to find specific andconcrete variables that have been previously studiedthat are aspects or examples of the ICF categories inthe domain set and that are relevant to the primaryfocus of the cohort study. The category specifica-tions are what the researcher needs to measure,either as a dependent or an independent variable. If,in the literature, a category specification has beenstudied with regard to its relationship with othervariables, then this information can be used by theresearcher to create hypotheses.

For environmental factors and some areas ofactivities and participation, the evidence for thecategory specification can often not be found in theliterature because very little research involving themeasurement of environmental factors exists. Inthese cases, an alternative approach was followed inthe SwiSCI study and reported in a separate article.7

The steps described below are taken for eachICF category in the domain set. In addition, it maybe necessary to create meaningful groups of ICFcategories rather than to perform searches onindividual categories. For example, if both s810Structures of the skin and b810 Functions of theskin are in the domain set, it would not be rea-sonable to perform two literature searches. In-stead, only one search needs to be performed onstudies on the skin (Fig. 1).

Electronic Literature SearchThe electronic search is performed for all rel-

evant databases (such as PubMed, EMBASE, Psyc-INFO, Cumulative Index to Nursing and AlliedHealth Literature, and the Social Sciences CitationIndex) using key terms that identify studies with thetarget population and keywords and MeSH termsthat address the content of the ICF Category.

Abstract SelectionSelection of abstracts is based on inclusion cri-

teria that focuses the search to those studies thatthe researcher believes are directly relevant to theaim and objectives of the cohort study, including



the analysis of the relationships between two ormore variables in the study design.

Extraction and Documentation ofInformation

The extraction and documentation of depen-dent and independent variables is performed at thesame time as the abstract check. Significant rela-tionships identified in the studies are also docu-mented. Whenever the abstracts do not provideenough information to check the inclusion criteriaor to extract the dependent and independent var-iables, the full-text paper is read. The extracteddependent and independent variables and relation-ships studied in the publication should be listedin the electronic database. To facilitate the furtherprocessing of the information, the names of thedependent and independent variables should behomogenized. For example, if the literature usesBemotional distress,[ Bemotional stress,[ and

Bemotional pressure,[ the most commonly usedterm Bemotional distress[ can be selected for allthree because they refer to the same phenomena.The significant relationships between dependentand independent variables should also be docu-mented. Of these variables, only those for whichthe definition of the ICF category or the group ofmeaningful categories applies are possible categoryspecifications.

Final DecisionThe final selection of the category specifica-

tions in the domain set involves two steps that arechallenging because they cannot be mechanicallyperformed but rely on the reasoning of experts infunctioning and the health condition. However,these steps ensure the quality of the study to beperformed.

First, the dependent and independent variablesextracted and the information about significant re-lationships found in the studies should be providedto experts in the cohort study health condition, withthe request that feedback on the relevance, suit-ability, and priority of the category specificationsand study questions be provided. Second, with all in-formation on hand, the study investigators shoulddecide on the set of variables that will be used tospecify the domain set and measured in the study.

RESULTSThe methodology described previously has been

followed in the case of SwiSCI with the followingresults.

SwiSCI Domain Set of What to MeasureThe complete list of ICF categories in the

SwiSCI Domain Set and their sources are pre-sented in Table 1.

Use of the ICF Categories of the MinimalGeneric Set

As mentioned in BMethods,[ the ICF categoriesof the Minimal Generic Set were the starting pointof the domain set of what to measure for SwiSCI(Table 1).

Identification of the Relevant Brief ICFCore Set for SwiSCI

The health condition under study in SwiSCI isSCI, both traumatic and nontraumatic. Two ICFCore Sets for SCI were developed, one for earlypostacute context and the other for the long-termcontext. The early postacute context was defined

FIGURE 1 Process followed for selecting categoryspecifications of what to measure.



TABLE 1 List of ICF categories and personal factors included in the SwiSCI domain set, as wellas the sources from which they have been identified.

Code ICF CategoriesMinimal

Generic SetBrief ICF Core Set for SCI

in the EPA ContextBrief ICF Core Set for SCI

in the LT Context

b130 Energy and drive functions xb152 Emotional functions x x xb280 Sensation of pain x x xb440 Respiration functions xb525 Defecation functions x xb620 Urination functions x xb640 Sexual functions xb710 Mobility of joint functions xb730 Muscle power functions x xb735 Muscle tone functions x xb810 Protective functions of the skin x xd230 Carrying out daily routine x xd240 Handling stress and other

psychologic demandsx

d410 Changing basic body position x xd420 Transferring oneself x xd445 Hand and arm use x xd450 Walking x xd455 Moving around x xd465 Moving around using equipment xd470 Using transportation xd510 Washing oneself xd520 Caring for body parts xd530 Toileting x xd540 Dressing xd550 Eating x xd560 Drinking xd850 Remunerative employment xe110 Products or substances for

personal consumptionx x

e115 Products and technology forpersonal use in daily living

x x x

e120 Products and technology forpersonal indoor and outdoormobility and transportation

x x x

e135 Products and technology foremployment

x

e150 Design, construction, andbuilding products and technologyof buildings for public use

x x

e155 Design, construction, and buildingproducts and technology ofbuildings for private use

x x

e225 Climate xe310 Immediate family x x xe320 Friends xe340 Personal care providers and

personal assistantsx x

e355 Health professionals x xe450 Individual attitudes of health professionals xe575 General social support services,

systems, and policiesx

e580 Health services, systems, and policies x xs120 Spinal cord and related structures x xs430 Structure of respiratory system x xs610 Structure of urinary system x xs810 Structure of areas of skin x

Because of space restrictions, the psychologic-personal factors included in the SwiSCI Domain Set are presented only in Ciezaet al. (unpublished data, 2011).

ICF, International Classification of Functioning, Disability, and Health; LT, long-term; EPA, early postacute; SCI, spinal cordinjury; SwiSCI, Swiss SCI Cohort Study.



as any kind of setting (e.g., acute hospital, rehabil-itation center, ambulatory care) in which the firstcomprehensive rehabilitation after the spinal cordlesion occurred is provided and to the variable pe-riod of time that begins and ends with the firstcomprehensive rehabilitation. The long-term con-text follows the early postacute period and typi-cally is the period during which persons with SCIlive in the community and may or may not receiveclinical care.

The ICF categories not already in the MinimalGeneric Set were added to the SwisSCI domain setfrom both Brief ICF Core Sets for SCI. ICF cat-egories from both core sets were added becauseSwiSCI will follow a cohort of persons with SCIfrom the onset of the lesion to the period whenthey are living in the community and for a still tobe determined open period of time that can lastmany years.8

The Brief ICF Core Set for the early postacutecontext contains 25 second-level categoriesVeightbody functions, three body structures, nine activi-ties and participation, and five environmental fac-tors. The Brief ICF Core Set for the long-termcontext contains 33 second-level categoriesV9body functions, 4 body structures, 11 activities andparticipation, and 9 environmental factors. The twoBrief ICF Core Sets have 39 ICF categories in total,and 13 are already in the Minimal Generic Set. Intotal, 45 ICF categories are included in the SwisSCIdomain set (Table 1).

Identification of Relevant Factors from thePsychologic-Personal Perspective

The process for the selection of factors relevantto the psychologic-personal perspective for SwiSCIis reported in a separate paper (Cieza et al., unpub-lished data, 2011).

Selection of Category Specifications ofWhat to Measure for SwiSCI

The selection of the specification of environ-mental factors and some activities and participa-tion strongly determined by environmental factors,such as d850 Remunerative employment, was car-ried out using other methods that are described ina separate article.7

Electronic Literature SearchTwenty-eight literature searches, one for each

of the meaningful groups of ICF categories of theSwiSCI Domain Set, were performed. In SwiSCI,the electronic systematic literature search was ex-

clusively performed in PubMed. For all the searchesperformed, the following SCI-specific search wasused:

#18 (#1) OR (#2) OR (#3) OR (#4) OR (#5) OR (#6)OR (#7) OR (#8) OR (#9) OR (#10) OR (#11)OR (#12) OR (#13) OR (#14) OR (#15) OR(#16) OR (#17)

#17 quadriplegia [tiab]#16 paraplegia [tiab]#15 tetraplegia [tiab]#14 spinal cord vascular diseases [tiab]#13 spinal cord neoplasm [tiab]#12 spinal cord compression [tiab]#11 Transverse Myelitis [tiab]#10 Spinal Cord Injury [tiab]#9 Spinal Cord Injuries [tiab]#8 quadriplegia [Mesh]#7 paraplegia [Mesh]#6 tetraplegia [Mesh]#5 spinal cord vascular diseases [Mesh]#4 spinal cord neoplasm [Mesh]#3 spinal cord compression [Mesh]#2 Myelitis, Transverse [Mesh]#1 Spinal Cord Injuries [Mesh]

From this point on, the ICF category b152Emotional functions will be used here to exemplifythe process (Fig. 2). Examples with complete infor-mation on the terms used to search the literaturefor all of the meaningful groups of ICF Catego-ries, the number of identified publications, and thenumber of selected studies are found in the firstfour columns of Table 2. Additional detailed infor-mation can be obtained from the authors uponrequest.

The following is the search for b152 Emotionalfunctions and was linked to SCI-specific search:

#25 (#19) OR (#20) OR (#21) OR (#22) OR (#23)OR (#24)

#24 (#18) AND mood [tiab]#23 (#18) AND feeling [tiab]#22 (#18) AND emotion*[tiab]#21 (#18) AND affect*[tiab]#20 (#18) AND anxiety [tiab]#19 (#18) AND depression [tiab]

Additional limits included that the publica-tion was not more than 10 yrs old, that the studypopulations included only adult humans, and thatit was written in English.

Abstract SelectionThe electronic search performed in PubMed re-

trieved 992 studies. The inclusion criteria were SCI



adult population; study performed in the last 10 yrs;published in English; and study focused on rela-tionships between emotional functions and at leastone additional variable. After applying the inclusioncriteria, 50 studies were included.

Extraction and Documentation ofInformation

The total number of variables after the homog-enization of their names was 50Vsome variableswere dependent, some independent, and othersboth dependent and independent in different stud-ies. Many different relationships were identified,with some variables (e.g., depression) being in-volved either as a dependent or an independentvariable in as many as 27 relationships. The def-inition of b152 Emotional functions was used to

identify potential category specifications of this ICFcategory, as marked in Table 3.

Final DecisionAfter an expert review of Table 3 in terms of

the relevance, suitability, and priority of the poten-tial category specifications, depression, anxiety, andfeeling were selected, merely on the grounds thatthese were the most common and that many of theother variables are already addressed in the domainset of factors from the psychologic-personal per-spective (Cieza et al., unpublished data, 2011). It isrecommended to document the arguments usedat this stage for later use as the study progressesand for the publication of the results.

DISCUSSIONIn this article, we have transparently described

an ICF-based approach that answers the questionof what to measure in a cohort study in which theprimary focus is to understand functioning as anoperationalization of health. The first measurementchallenge with cohort studies is to be efficient inthe number of study variables used and to be ef-fective in selecting the right variables. Because theapproach builds on the strong methodologic basisof the Minimal Generic Set and the ICF Core Setsfor specific health conditions, the cohort study re-searcher can be confident that the categories andcategory specifications identified in the domain setwill be relevant to the salient features of the expe-rience of living with a health condition. It will benoticed that some chapters of Activities and Par-ticipation are not represented in this list; in par-ticular, there are no categories from Chapter 6,Domestic Life; Chapter 7, Interpersonal Interac-tions and Relationships; and Chapter 9, Commu-nity, Social, and Civic Life. As described in aseparate article7 addressing this issue, researchersconsulted the Comprehensive Core Sets for SCIand the ICF Core Set for vocational rehabilita-tion because it is crucial for integration into thelabor market, one of the major concerns of personswith SCI.

Comparability of data is facilitated by this ap-proach because the ICF is the international stan-dard language for health information, and thedomain set is composed entirely of ICF categoriesor specifications of them. Comparability is furtherenhanced because the domain set includes, by de-fault, the Generic ICF Set, which is the minimalset of ICF categories that must be considered in

FIGURE 2 The process of selecting category specifi-cations for b152 Emotional functions inSwiSCI. SwisSCI indicates Swiss SpinalCord Injury Cohort Study; ICF, Interna-tional Classification of Functioning, Dis-ability, and Health.



TABLE 2 Examples of meaningful groups of ICF categories for which the specific searches wereperformed, of the specific terms used to search the literature, of the number of identifiedpublications, of the number of selected studies, and of the selected category specificationsto be included in SwiSCI

Meaningful Groups of ICFCategories of the SwiSCIDomain Set

Terms Used inSearches

Number ofIdentified

Publications

Number ofSelected

PublicationsSelected CategorySpecifications

Structure of pelvicregion

Urinary Bladder [Mesh] 489 230 Continence

Structure of urinarysystem

Urinary BladderDiseases [Mesh]

Kind of voiding the bladder(e.g., indwelling catheter,intermittent self-catheterization)

Urinary excretoryfunctions

Urologic SurgicalProcedures [Mesh]

Self-rated amount respectivelyhealth-professional rated amountof assistance/independencyfor bladder management

Urination functions Urination Disorders[Mesh]

Use of external assistive devices(e.g., condom catheter or diapers)

Sensations associatedwith urinaryfunctions

Urinary Catheterization[Mesh]

Prod and technologyfor personal use indaily living

Urination [Mesh]

Urinary Bladder [TIAB]Urinary BladderDiseases [TIAB]

Urologic SurgicalProcedures [TIAB]

Urination Disorders[TIAB]

Urinary Catheterization[TIAB]

Urination [TIAB]Structure of areas ofthe skin

Pressure ulcer [TIAB]and [Mesh]

532 123 Prevalence of pressure ulcer(localization and severity)(b810 and s810)

Protective functions ofthe skin

Skin care [TIAB] and[Mesh]

Repair functions ofthe skin

Sweating [TIAB] and[Mesh]

Other functions ofthe skin

Skin [TIAB] and [Mesh]

Sensations relatedto the skin

Carrying out dailyroutine

Activities of daily living[TIAB] and [Mesh]

336 76 Self-rated amount respectivelyhealth-professional ratedamount of assistance/independency for:

Washing oneself ADLs [TIAB] Eating (d550)Caring for body parts Instrumental activities

of daily living [TIAB]IADLs [TIAB]

Washing upper and lowerbody (d510)

Toileting Dressing and undressing upperand lower body (d540)

Dressing Grooming (d520)Eating Toileting (d530)Drinking Use of assistive devices for

ADLs (e115)Living situation at admittance at firsthospital stay after SCI, at dischargefrom first hospital stay after SCI,and in the long term (as Bproxi[for independency in ADLs)

ICF, International Classification of Functioning, Disability, and Health; SCI, spinal cord injury; SwiSCI, Swiss SCI Cohort Study.



any research on functioning and health.4 This com-parability of data extends both across time, anessential requirement of cohort studies in general,and across healthcare settings, an important re-quirement of cohort studies such as the SwiSCI,in particular. Moreover, because the ICF is an in-ternational classification widely used across healthprofessions, setting and sectors, the cohort studyresults will be both widely understood and usablein various contexts, including health and socialpolicy.

In an emerging research area such as humanfunctioning sciences in which the primary focus isthe understanding of functioning and health, theapproach described here will be especially valuableto researchers working in this area. Only with aconceptually based approach is there the potentialof enabling researchers to go beyond standardhealth research questions and paradigms towardnovel ways of understanding health from the per-spective of the lived experience. Rather than rely di-rectly on standard measurement instruments and

TABLE 3 Independent and dependent variables identified in the search for b152 Emotional functions

Independent Variable Dependent Variable

1. Depression(3,4,5,7,8,9,13,15,16,17,21)

1. Depression (depressive symptoms) (2,3,4,5,6,7,8,9,10,11,12,14,15,16,18,19,20,21,22,23,24,26,28,29,31,33)

2. Coping behavior-strategies (fight spirit,acceptance) (1,2,3,7,10)

2. Anxiety (2,4,5,7,8,9,10,12,18,22,26,32)

3. Anxiety (1,3,5,7,8,13,16) 3. Emotional distress (1,2,3,6,12,20,21)4. Physical Activities (1,2,9,11) 4. Quality-of-life/perceived quality-of-life (1,9,26)5. Pain (1,2,6,20) 5. Life satisfaction (postrehabilitation subjective well-being)

(1,3,14,17)6. SCI characteristics (1,3,12) 6. Mood (5,9,10,24)7. Group-based (1,2) intervention 7. Posttraumatic Stress Disorder (1,2,3,13)8. Appraisals (1,2) 8. Work-Employment Status (1,3)9. Stress (1,2,4,6) 9. Pain (1,4,19)10. Health status (1,2,6) 10. Rehabilitation outcome (2,17)11. Bowel functions/management (1) 11. Feelings (4,30)12. Functioning 12. Positive/negative affects/affective well-being (6)13. Emotional distress (7,14,15) 13. Future time orientation (1,3)14. Emotions (1,5,14) 14. Physical performance/physical activity (13,14)15. Age (1) 15. Participation (1,13)16. Time since injury (1) 16. Adaptation to SCI (1,3)17. Positive/negative affects (5,10) 17. Self-efficacy (1)18. Sense of coherence (1,2) 18. Stress (23)19. Locus of control (1,9) 19. Emotional attributes (27)20. Sex (1,3) 20. Emotional functioning (5)21. Social support (1,3) 21. Medical Complications (1)22. Social self-efficacy (1,2) 22. Coping (27)23. Health-related quality-of-life (1,18)24. Life satisfaction (1,6)25. Mood (4)26. Education (1,2)27. Autonomic response (19,22)28. Level of mobility (1)29. Personality dimensions (NEO five factor

inventory) (1)30. Rehabilitation Environment 11)31. Marital Status (1)32. Incontinence (fecal) (2)33. Helplessness (1)34. Hospital discharge35. Negative attitudes toward emotional

expression36. Completeness of injury37. Participation38. Medical complications39. Self-efficacy40. Life satisfaction41. Perceived emotional functioning

Potential category specifications are in boldface. The numbers next to the independent variable refer to their relationships withthe dependent variables and vice versa.

NEO, Neuroticism-Extroversion-Openness.



on identifying what to measure based on them, thisapproach transparently and comprehensibly makesit possible to take a fresh look at the requirementsof measurement: first, define what to measure interms of its importance to our understanding ofhealth and living with a health condition and onlythen look at the more technical issues of how tomeasure. In addition, the process of selecting cat-egory specifications has the added value of generat-ing potentially valuable research questions. Forexample, the study question, BWhat is the influenceof depression on medical complication,[ can be de-rived from Table 3 in which the process for selectingthe specifications for the category b152 Emotionalfunctions was described.

There is a potential application of this approachthat should be mentioned. As the process for up-dating the ICF has now been initiated by the WorldHealth Organization, the data gathered using thisICF-based approach would provide highly relevantevidence for updating proposals. For example, ifthe cohort researcher, while searching for a spec-ification of an ICF category, makes a proposal thatis not explicitly mentioned in the definition of thatcategory, the data gathered could provide an evi-dence base for the updating decision to add thatspecification to the ICF definition, or indeed tocreate a new ICF category.

As with any new approach, however, what isdescribed here also presents challenges. The firstis that defining what to measure without consider-ation of the practicalities of how to measure meansthat the Domain Set may contain ICF categories orcategory specifications that cannot be easily as-sessed, such as interpersonal relationships, spiri-tuality, or political life and citizenship. Not takingaccount of assessment practicalities may limit theeffectiveness of the cohort study or the usefulnessof its conclusions. However, by highlighting themost relevant variables to measure, the researcherstill has the option of setting aside some of thesefor cost or methodologic reasons and for comingback to them later should new approaches to mea-surement become available.

The second challenge arises when there is noICF Core Set for the health condition under con-sideration. In that case, an evidence-based proce-dure, following the methodology of the ICF CoreSet development,6 could be used to determine a setof ICF categories that is comprehensive enough todescribe the functioning of the target populationbut does not contain more categories than is nec-essary to do so. This is time consuming and wouldadd considerable burden to the performance of the

cohort study, although the methodology is well es-tablished and easily available.11

CONCLUSIONSCohort studies are time-consuming and

resource-intensive endeavors, making it necessaryto select research questions, measurement instru-ments, and category specifications with great care.This is especially true of cohort studies in whichthe main focus is the understanding of function-ing over time for a specific population, such as theSwiSCI study. In this paper, we have proposed anICF-based approach to define the first major stepof measurement, namely what to measure. This ap-proach is a valuable tool for the cohort researcherbecause it guarantees the comparability of data andcomprehensiveness of scope, enhancing the pro-spects of the study results being understood andconsequently used by different health profession-als and in a different context, including health andsocial policy.

ACKNOWLEDGMENTS

We thank the following researchers at theSwiss Paraplegic Research and at the Institute forHealth and Rehabilitation Sciences for the valu-able contribution in the process of defining thedomain set for SwiSCI: Jorg Brechbuhl, MartinBrinkhof, Antonia Coppin, Angela Frotzler, AliciaGarza, Andrea Glassel, Szilvia Geyh, Felix Gradinger,Roger Hilfiker, Elisabeth Linseisen, Gabi MullerVerbiest, Rachel Muller, Christine Muff, SylviaNeubert, Claudio Peter, Alexandra Rauch, JanReinhardt, Stefan van Drongelen, Inge-Marie Velstra,and Erik von Elm.

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3. World Health Organization: International Classifi-cation of Functioning, Disability and Health: ICF.Geneva, Switzerland: WHO; 2001

4. Rothman KJ, Greenland S: Modern epidemiology.ed 2. Philadelphia, PA: Lippincott Williams & Wilkins;1998

5. Escorpizo R, Graf S, Marti A, et al: Domain sets andmeasurement instruments on participation and en-vironmental factors in spinal cord injury research.Am J Phys Med Rehabil 2011;90(suppl 2):S66Y78



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https://www.researchgate.net/publication/11366024_Application_of_the_International_Classification_of_Functioning_Disability_and_Health_ICF_in_Clinical_Practice?el=1_x_8&enrichId=rgreq-93c67947-0b66-40f6-880e-a66717743bc3&enrichSource=Y292ZXJQYWdlOzIyMTY5OTE0ODtBUzoxMjk5OTAxOTI1Mzc2MDJAMTQwODAwMzQ4NTcwMA==




https://www.researchgate.net/publication/299170536_ICF-based_classification_and_measurement_of_functioning?el=1_x_8&enrichId=rgreq-93c67947-0b66-40f6-880e-a66717743bc3&enrichSource=Y292ZXJQYWdlOzIyMTY5OTE0ODtBUzoxMjk5OTAxOTI1Mzc2MDJAMTQwODAwMzQ4NTcwMA==



setting up a cohort study on functioning

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