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AACPDM 2013 Clinical Use of FAQ 1 Clinical Use of the Gillette Functional Assessment Questionnaire: Translating Research into Clinical Practice Jean Stout, PT, MS Rocio Riveros-Charry, PT Acknowledgements Funding Sources & Collaborators Medical Education & Research Association 2008 Clinical Research Planning Grant (Tucker) Carole Tucker George Gorton Anita Bagley Raymond Tervo Tom Novacheck Outline Motivation Review of the Gillette Functional Assessment Questionnaire Rasch Analysis Assessing Development Clinical Scenarios Functional Assessment Questionnaire Novacheck et al. 2000 Gorton et al. 2011 Stout et al. 2012 Tervo et al. 2002 The reliability and validity of the Gillette Functional Outcome Questionnaire. JPO 20:75-81, 2000 Correlation between physical findings and gait measures in children with cerebral palsy. DMCN 44:185-190, 2002 The Gillette Functional Assessment Questionnaire 22-item skill set: Factor & Rasch Analysis. DMCN 53:250-255, 2011 Rasch Analysis of items from two self-report measures of motor function: Determination of item difficulty and relationships with children’s ability levels. DMCN 54:443- 450, 2012 Practice of Evidence Based Treatment Influence Reimbursement Patterns Critically Evaluate Effectiveness of Treatments Motivation Motivation ICF

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Page 1: Acknowledgements Clinical Use of the Gillette Funding ... · Clinical Use of the Gillette Functional Assessment Questionnaire: Translating Research into Clinical Practice Jean Stout,

AACPDM 2013 Clinical Use of FAQ 1

Clinical Use of the Gillette Functional Assessment

Questionnaire: Translating Research into Clinical Practice

Jean Stout, PT, MSRocio Riveros-Charry, PT

AcknowledgementsFunding Sources & Collaborators

Medical Education & Research Association

2008 Clinical Research Planning Grant (Tucker)

Carole TuckerGeorge GortonAnita Bagley

Raymond TervoTom Novacheck

Outline•Motivation•Review of the Gillette Functional Assessment Questionnaire• Rasch Analysis•Assessing Development•Clinical Scenarios

Functional Assessment Questionnaire Novacheck et al. 2000

Gorton et al. 2011

Stout et al. 2012

Tervo et al. 2002

The reliability and validity of the Gillette Functional Outcome Questionnaire. JPO 20:75-81, 2000

Correlation between physical findings and gait measures in children with cerebral palsy. DMCN 44:185-190, 2002

The Gillette Functional Assessment Questionnaire 22-item skill set: Factor & Rasch Analysis. DMCN 53:250-255, 2011

Rasch Analysis of items from two self-report measures of motor function: Determination of item difficulty and relationships with children’s ability levels. DMCN 54:443-450, 2012

Practice of Evidence BasedTreatment

Influence Reimbursement Patterns

Critically Evaluate Effectiveness of Treatments

Motivation Motivation

ICF

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AACPDM 2013 Clinical Use of FAQ 2

Motivation

ICF

what a child is able to do in an ideal environment

Capacity

Capability A child’s capacity influenced by environmental factors and choice

Performancewhat a child actually does in the environment in which they live

So What Is the Challenge?

Dx: Autism; In-toeing

Difficulty keeping up

Unable to ride a two-wheel bike

The Challenge? Unable to ride a two-wheel bike

The Challenge? Walk up/down stairs using a railingStand washing hands at sink

The Challenge?The family rates his walking at a level 9He is able to do 16 of 22 advanced functional skills

age 7 (16 of 22)

age 4 (10 of 22) age 5 (13 of 22)

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AACPDM 2013 Clinical Use of FAQ 3

age 4age 7 age 5

Are these the right skills for each age?

Age 3

So What Is the Challenge?

GMFCSFMS

4.75x typical

III

3,3,1

Integration !

Skill Mastery of Typically Developing Children Using the Gillette Functional Assessment

Questionnaire

1) To acquire normative data on both the 22 queried skills and the walking scale on the FAQ

2) To establish the range and type of skills a child would be expected to perform based on a given FAQ walking level

Purpose:

Validation of FAQ-22 Skill Set

Rank Order with Classification Systems

Functional Assessment Questionnaire Novacheck et al. 2000

Gorton et al. 2011

Stout et al. 2012

Tervo et al. 2002

The reliability and validity of the Gillette Functional Outcome Questionnaire. JPO 20:75-81, 2000

Correlation between physical findings and gait measures in children with cerebral palsy. DMCN 44:185-190, 2002

The Gillette Functional Assessment Questionnaire 22-item skill set: Factor & Rasch Analysis. DMCN 53:250-255, 2011

Rasch Analysis of items from two self-report measures of motor function: Determination of item difficulty and relationships with children’s ability levels. DMCN 54:443-450, 2012

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AACPDM 2013 Clinical Use of FAQ 4

Functional Assessment Questionnaire 10 Level Walking Scale

10

62

Functional Assessment Questionnaire 10 Level Walking Scale

Functional Assessment Questionnaire 22 Advanced Functional Skills

FAQ validationNovacheck, Stout, Tervo. J Pediatr Orthop 2000

Wee

Fim

Gai

t Ind

ex

O2

Cos

t

PO

DC

I T/B

M

PO

DC

I Glo

bal

FAQ

Questions/Discussion?Methods:

Cross-sectional survey design of parents of children between 9 months and 9 years of age

Challenge:Because of the broad range of typical development for each skill, statistical power analysis of needed numbers depended on the proportion of children who were able to perform any given skill at any given age levelA preliminary power analysis estimated the probability to detect a +10% difference if the proportion of the population able to perform any skill within the age category is 50%

Target: N=75 every 6 month interval (9 months – 9 years)

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AACPDM 2013 Clinical Use of FAQ 5

Results:977 total surveys through 2010

response rate (.005 - 40%) average 20%

810 no co-morbidities (83%)

523 M ; 454 F

73% white; 11% black; 10% multi-racial

19% qualify for medicaid/medical assistance

796 surveys <6 years of age (81%)

Results:

0

25

50

75

100

125

150

175

200

225

1 2 3 4 5 6 7 8 9 10

0

2550

75100

125150

175200

225

<1 1 2 3 4 5 6 7 8 9 >10

Age in Years

FAQ Level

Skill by Age How Are The Ranks Determined?Rank Description Total Able Percent1 Walk carrying an Object 746 92%

2 Maneuver in Tight Areas 716 88%

3 Runs 716 88%

4 Step Over Object Right Foot First 704 87%

5 Step Over Object Left Foot First 700 86%

6 Runs with Control 700 86%

7 Walks Carrying a Fragile Object 694 85%

8 Walk Up/Down Stairs with Railing 693 85%

9 Walk Carrying a Fragile Object 692 85%

10 Kick Ball with Left Foot 681 83%

11 Step Backward 677 83%

12 Step Up/Down Curb Independently 661 82%

13 Walk Up/Down Stairs Without Railing 598 72%

14 Jump Off Single Step 584 70%

15 Ride a Three Wheel Bike 569 68%

16 On/Off Escalator Without Help 501 62%

17 On/Off Bus Independently 465 57%

18 Hop on Right Foot 430 46%

19 Hop on Left Foot 417 44%

20 Ice Skate/Roller Skate Independently 263 32%

21 Ride a Two Wheel Bike Wout Training Wheels 188 23%

22 Jump Rope 169 21%

Easist

Most Difficult

Walking Level by Age (up to age 2 1/2)

<1 12-18 mos.

24-30 mos.18-24 mos.

Walking Level by Age (up to age 3)

<1 <1-1.5 <1.5-2<2-2.5

<2.5-3

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AACPDM 2013 Clinical Use of FAQ 6

Skill by FAQ LevelAge 3

Questions/Discussion? Problem

•Classical Test Theory Depends on a Normal Distribution Across Levels of Measurement

•Issue for Validation of FAQ-22 in Children with Gait Impairment

•Item-Response Theory & Rasch Analysis

0

2550

75100

125150

175200

225

<1 1 2 3 4 5 6 7 8 9 >10

Rasch & Item Response Theory Analysis

Rasch Analysis: A mathematical logistic model that determinesa person’s ability (relative to the ability of each other person) and the difficulty of an item (relative to the difficulty of all other items) and places them on the same interval measurement scale

person abilityitem difficulty

How Does It Actually Work?

Start out Comparing Each to the Other

object to be measured

person ability

reference for comparison

item difficulty

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AACPDM 2013 Clinical Use of FAQ 7

How Does It Actually Work?

Score=0 Score=1

How Does It Actually Work?

Items

Person 1

How Does It Actually Work?

Items

Item 1 score=0

Person 1

How Does It Actually Work?

Items

Item 2 score=1

Person 1

How Does It Actually Work?

Items

Item 3 score=1

Person 1

How Does It Actually Work?

Items

Item 4 score=0

Person 1

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AACPDM 2013 Clinical Use of FAQ 8

How Does It Actually Work?

Items

P1 0 1 1 0

How Does It Actually Work?

Items

P1 0 1 1 0

P2 1 1 1 1

P3 0 1 0 0

P4 0 1 1 1

How Does It Actually Work?

Reorder People

P3 0 1 0 0

P1 0 1 1 0

P4 0 1 1 1

P2 1 1 1 1

How Does It Actually Work?

Re-Order Items

P3 0 0 0 1

P1 0 0 1 1

P4 0 1 1 1

P2 1 1 1 1

1 2 3 4

How Does It Actually Work?

Hardest

P3 0 0 0 1

P1 0 0 1 1

P4 0 1 1 1

P2 1 1 1 1

1 2 3 4

Easiest

Least Able

Most Able

How Does It Actually Work?

Items

P3 0 0 0 1

P1 0 0 1 1

P4 0 1 1 1

P2 1 1 1 1

1 2 3 4

Categories: [Easy, A Little Hard, Very Hard, Can’t Do]

FAQ – Polytomous Scoring

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AACPDM 2013 Clinical Use of FAQ 9

Results:Gait Impaired

Frequency Distribution of Subjects by Level of Ability

Difficulty of Skills

Results:Typ Develop

Frequency Distribution of Subjects by Level of Ability

Difficulty of Skills

Gait ImpairedTyp Dev

ResultsRank Order of Skills

Results

What Was Next?

Challenge:

Establish an appropriate, clinically meaningful way to integrate multiple measures into a single perspective of how each relates to the other.

What Was Next?

Retrospective study N=485 First time gait analysisAcross GMFCS levels I – IVAll diagnoses (not just CP)Ages: <19 years oldFAQ+PODCI

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AACPDM 2013 Clinical Use of FAQ 10

Measures

Objective Self ReportClassification Systems

Gait Deviation Index

PODCIFAQ - Skills

GMFCS LevelFAQ Walking

Results:

Person Ability or Item Difficulty

Rasch-derived Person Ability Map of Function and Walking Ability

Results:Item # Description Measure

(logits)FAQ Walking Level 9 Mean

Ability; 95% CI:1.12,1.451.18

F04 Walk up and down stairs without using the railing

Runs well including around a corner with good control

0.92

F22 Ride an escalator, can step on/off without help

0.72

F12 Jumps off a single step independently

0.43

FAQ Walking Level 8 Mean Ability; 95% CI:0.18,0.55

0.32

GMFCS Level II 0.24F06 runs 0.19F18 Kick a ball with left foot -0.19

F07 0.84

Can get on/off bus by self 0.25

Person Ability or Item Difficulty

Rasch-derived Person Ability Map of Function and Walking Ability

Clinical Scenarios Remember Blake?The family rates his walking at a level 9He is able to do 16 of 22 advanced functional skills

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AACPDM 2013 Clinical Use of FAQ 11

Remember Blake?Skills by Age

Remember Blake?Skills by Walking Level

Scenario I: BlakeScenario II

Child who walks at FAQ-WL8 & is able to run, but can’t play hopscotch or skip with friends.

Clinician: Ability to hop is beyond her capability at WL 8, but should be able to “jump off a single step”.

Scenario IIIUnable to ride a two-wheel bike

Scenario III

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AACPDM 2013 Clinical Use of FAQ 12

Scenario III

Clinician: Mismatch of skills & walking level

Plan: Determine whether mismatch is skills or walking level. Add:Skills that may be present in the gaps

Scenario IVUnable to jump off a single step

GMFCS Level II

Scenario IV Scenario IV

Clinician: Not a clear mismatch of skills, but many abilities are reported as “very hard” to perform

Plan: Determine whether mismatch is skills or walking level. Add:Skills that may be present in the gaps

Scenario V

3 yr. old who walks at FAQ-WL 10 & is able to do 11 of 22 advanced skills. Crawls at home for primary mobility

Clinician: Mismatch of skills & walking level

Person Ability or Item Difficulty

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AACPDM 2013 Clinical Use of FAQ 13

Scenario V

Clinician: Mismatch of skills & walking level

Plan: Determine whether mismatch is skills or walking level. Add:Skills that may be present in the gaps

Scenario VI Walk up/down stairs using a railing

Stand washing hands at sink

Scenario VIScenario VI

Clinician: Mismatch of skills & walking level,GMFCS

Plan: Add skills that may be present in the gaps

Scenario VII Walk one block

Scenario VII

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AACPDM 2013 Clinical Use of FAQ 14

Use Before & After Intervention?

Scenario IV-GMFCS II

Pre-Ortho Post-Ortho

GMFCS IVPre-SDR

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AACPDM 2013 Clinical Use of FAQ 15

Post-SDRConclusion

Framework to Link Outcome Tools & Classification Systems

Guides Counseling of Families Regarding Functional Expectations

Treatment Planning to Choose Skills within Child’s Capability

Questions?Discussion?

Thank [email protected]@gillettechildrens.com

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From

: Stout JL, et al. D

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From

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Skills By Age

Based on Stout J et al. Unpublished data. N=977 parent-report FAQ data of typically developing children. Each cell represents the percentage of children at each age able to perform a particular skill.

Skill <1 1-1.5 1.5-2 2-2.5 2.5-3 3-3.5 3.5-4 4-4.5 4.5-5 walks carrying an object 19 92 98 100 100 100 100 100 100 runs 6 67 98 100 100 100 100 100 100 manuever in tight areas 1 72 96 100 100 100 100 100 100 step over object R foot 3 66 89 89 99 100 100 100 100 step over object L foot 3 65 89 89 96 100 100 100 100 runs well w/control 3 53 95 98 100 100 100 100 100 kick ball R foot 0 55 92 97 97 100 100 100 100 walks up/down stairs with railing 0 50 89 100 100 100 100 100 100 step backward 0 41 89 93 93 100 100 100 100 kick ball L foot 0 51 86 95 96 99 100 100 100 step up/down curb 0 34 69 98 99 100 100 100 100 jump off single step 0 3 36 73 91 99 100 100 100 walks carrying a fragile object 0 5 50 100 100 100 100 100 100 walk up/down stairs w/o railing 0 7 37 86 93 100 100 100 100 ride 3 wheel bike 0 2 30 76 84 96 96 100 100 on/off escalator w/o help 0 0 10 44 64 82 88 96 96 on/off bus 0 0 0 25 48 69 90 90 96 hop right foot 0 0 0 14 28 56 81 98 98 hop left foot 0 0 0 10 22 46 80 98 98 ice skate/roller skate 0 0 0 17 15 23 30 45 57 ride 2 wheel bike 0 0 0 0 0 6 0 20 26 jump rope 0 0 0 0 0 0 0 2 6

Page 19: Acknowledgements Clinical Use of the Gillette Funding ... · Clinical Use of the Gillette Functional Assessment Questionnaire: Translating Research into Clinical Practice Jean Stout,

Rasch analysis of items from two self-report measures of motorfunction: determination of item difficulty and relationships withchildren's ability levels

JEAN L STOUT1 | GEORGE E GORTON III2 | TOM F NOVACHECK1 | ANITA M BAGLEY3 | RAYMOND C TERVO1 |KATHERINE BEVANS4 | CAROLE A TUCKER5

1 Gillette Children's Specialty Healthcare, St Paul, MN; 2 Shriners Hospitals for Children, Springfield, MA; 3 Shriners Hospitals for Children- Northern California Unit,Sacramento, CA; 4 Children's Hospital of Philadelphia, Philadelphia, PA; 5 Temple University, Philadelphia, PA, USA.

Correspondence to Jean L Stout at James R Gage Center for Gait and Motion Analysis, Gillette Children's Specialty Healthcare, 205 East University Avenue, St Paul, MN 55101, USA. E-mail:[email protected]

This article is commented on by Gates on pages 391–392 of this issue.

PUBLICATION DATA

Accepted for publication 18th November 2011.Published online 14th March 2012.

ABBREVIATIONSFAQ Gillette Functional Assessment

QuestionnaireFAQ-WL Gillette Functional Assessment

Questionnaire walking scale levelGDI Gait Deviation IndexPODCI Pediatric Outcome Data Collection

InstrumentSPF Sports and physical functionTBM Transfers and basic mobility

AIM The aim of this article was to determine item measurement properties of a set of items

selected from the Gillette Functional Assessment Questionnaire (FAQ) and the Pediatric Outcome

Data Collection Instrument (PODCI) using Rasch analysis, and to explore relationships between

the FAQ ⁄ PODCI combined set of items, FAQ walking scale level, Gross Motor Function Classifica-

tion System (GMFCS) levels, and the Gait Deviation Index on a common measurement scale.

METHOD Rasch analysis was performed on data from a retrospective chart review of parent-

reported FAQ and PODCI data from 485 individuals (273 males; 212 females; mean age 9y 10mo,

SD 3y 10mo) who underwent first-time three-dimensional gait analysis. Of the 485 individuals, 289

had a diagnosis of cerebral palsy (104 GMFCS level I, 97 GMFCS level II, 69 GMFCS level III, and 19

GMFCS level IV). Rasch-based person abilities and item difficulties based on subgroups defined

by the FAQ walking scale level, Gait Deviation Index, and the GMFCS level were compared.

RESULTS The FAQ ⁄ PODCI item set demonstrated necessary Rasch characteristics to support its

use as a combined measurement scale. Item groupings at similar difficulty levels were consistent

with the mean person abilities of subgroups based on FAQ walking scale level, Gait Deviation

Index, and GMFCS level.

INTERPRETATION Rasch-derived person ability scores from the FAQ ⁄ PODCI combined item

set are consistent with clinical measures. Rasch analysis provides insights that may improve

interpretation of the difficulty of motor functions for children with disabilities.

Improvements in mobility, ambulation, and enhanced partici-pation in activities with family and peers are often identified asprimary goals of clinical and surgical interventions for childrenand adolescents with physical impairments. Clinical measure-ment of ambulation and functional mobility can be accom-plished using a variety of measures including instrumentedgait analysis, standardized clinical assessments of gross motorskills, and ⁄ or self-reported outcomes. Despite concern aboutthe accuracy of self- ⁄ proxy report,1–3 the perspective providedby the affected individual and ⁄ or family adds important insightinto both goal setting and the assessment of outcome.

The reporting of multiple assessments, however, is complex.The International Classification of Functioning, Disability;and Health (ICF) framework4 has become an important orga-nizing framework for health and disability in rehabilitationresearch. Within the ICF framework, an activity is defined asthe execution of a task or action by an individual. Participationis defined as involvement in a life situation. The ICF providestwo qualifiers for activity and participation: (1) ‘capacity’ – what

a child is able to do in an ideal environment, the highest func-tioning level; and (2) ‘performance’ – what a child actually doesin the environment in which they live. Since the ICF’s emer-gence in 2001, the use of these ICF qualifiers, along with ‘capa-bility’ – a child’s capacity influenced by environmental factorsand choice – have become increasingly important in clinicalresearch, particularly in assessing treatment efficacy anddescribing the range of function for the child with a disabil-ity.5–7 Existing validated instruments often predate the emer-gence of the ICF, and may include within a single instrumentitems that measure capability, capacity, or performance, andgenerically use words (capable, skill, ability, etc.) in their instru-ment description that now have additional, specific ICF-relatedmeanings. The fact that existing instruments often blend mea-surement of different ICF components and qualifiers of func-tioning and disability complicates the issues faced by cliniciansand researchers in their choice of appropriate instruments.

Ideally, a comprehensive battery of instruments chosen tocharacterize function would be structured to ‘fit’ together to

ª The Authors. Developmental Medicine & Child Neurology ª 2012 Mac Keith Press DOI: 10.1111/j.1469-8749.2012.04231.x 443

DEVELOPMENTAL MEDICINE & CHILD NEUROLOGY ORIGINAL ARTICLE

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provide the greatest breadth of assessment, with each measureadding complementary information about the person’s statuswithout adding redundancy. Often, however, each instrumentin a given battery is reported in isolation from the others –lacking a common context of how each relates to the others.Approaches that provide common measurement across instru-ments can help to reduce the complexity introduced by theuse of multiple instruments.

Rasch analysis can be used to create a common, continuousinterval-level measurement scale for estimates of both ‘personability’ (how much of the underlying construct the persondemonstrates) and ‘item difficulty’.8 The Rasch terms‘person ability’ and ‘item difficulty’ have a specific meaning inthis context. This person item mapping indicates the probabil-ity that an individual of a certain ‘person ability’ can performspecific items based on each ‘item’s difficulty’. Recent outcomeassessments of physical function have used Rasch or itemresponse theory analyses to more fully evaluate the measure-ment properties of the instruments on an item-level basis9–14

and in designing functional staging systems which have beenfound to be useful in enhancing clinical decision making.15,16

The Gillette Functional Assessment Questionnaire(FAQ)10,17 and the Pediatric Outcome Data Collection Instru-ment (PODCI)9,18–21 are self- ⁄ parent-report measures ofphysical abilities commonly used in pediatric clinical practice.Both are often used in conjunction with the Gross MotorFunction Classification System (GMFCS)22,23 to describefunction and walking ability in children with cerebral palsy(CP).24–26 The FAQ consists of a 10-level classification ofwalking ability (FAQ walking scale level or FAQ-WL) and 22functional activities rated on a five-point Likert difficulty scale(FAQ-22). The FAQ-WL portion of the FAQ has been vali-dated as a measure of functional walking status.17 The PODCIconsists of 86 items divided into eight subscales. The PODCIis ‘designed to assess overall health, pain, and participation innormal daily activities as well as in more vigorous activitiesassociated with young people.’18 The transfers and basicmobility (TBM) subscale consists of 11 items, and the sportsand physical function (SPF) subscale consists of 21 items (12tasks and nine conditional responses). PODCI test scores andsubscales have been shown to be reliable and valid.19 Factor-and item-level properties of both the FAQ and PODCI instru-ments have been previously reported.9,10 Items contained inboth measures (FAQ and PODCI) reflect a blend of ICFactivity and participation concepts because the ICF emergedafter the development of these instruments. Therefore, theunderlying construct being assessed by these instruments isreflective of more general physical functioning.

Rasch analysis can be used to establish the relationshipbetween items from the FAQ-22 and PODCI TBM ⁄ SPF itemson a common difficulty scale. Subsequent stratification of indi-viduals based on classification systems such as the FAQ-WLand GMFCS and measures of gait impairment such as the GaitDeviation Index (GDI)27 may reveal additional relationships,which will allow clinicians to have a higher level of confidencethat certain physical skills tend to be associated with a specificclassification of functional mobility or gait impairment.

The purposes of this study were to assess the factor- anditem-level properties of a combined FAQ-22 and PODCITBM ⁄ SPF item set, and to explore the associations betweenthe Rasch-ordered combined FAQ-22 ⁄ PODCI TBM ⁄ SPFitem set, with participant groupings based on the FAQ-WL,GMFCS, and GDI.

METHODA retrospective medical record review of FAQ (FAQ-WL andthe FAQ-22), PODCI (TBM ⁄ SPF scale), and GDI data wasconducted on a group of children and young adults (<19y)who underwent first-time gait analysis in a tertiary hospitalsetting between January 2006 and June 2008. GMFCS levelwas included for children with a diagnosis of CP. FAQ andPODCI data were obtained by proxy report of the parents orlegal guardian as part of the routine clinical gait analysis. AllFAQ-22 items, nine of 11 PODCI-TBM subscale items, andfive of 12 PODCI-SPF subscale items scored on a similar five-point Likert difficulty scale were included for analysis. Thetwo excluded TBM items measure frequency of assistanceneeded, a different construct, rather than a specific physicalskill. The excluded SPF items either measure frequency ofassistance needed or are structured as multiple responses to asingle item with conditional responses that are not on a five-point Likert difficulty scale which did not allow these items tobe included in the analysis. Waiver of informed consent andHealth Insurance Portability and Accountability Act authori-zation were obtained for this study from the local institutionalreview board. Individuals whose families had opted out of useof medical records for research were excluded.

Statistical analysisExploratory and confirmatory factor analysis was conductedusing MPlus 5.1 software28 to validate the structure of thecombined FAQ-22 ⁄ PODCI TBM ⁄ SPF item set. Model fitwas examined via multiple indices including the ConfirmatoryFit Index, the Tucker–Lewis Index, and standardized rootmean square residual. Confirmatory Fit Index and Tucker–Lewis Index values greater than 0.95 and a standardized rootmean square residual less than 0.08 indicate good fit of themodel to the data. Data were tested to ensure that the statisti-cal assumptions for Rasch analyses were met. The Rasch rat-ing scale model was implemented using Winsteps software29

to simultaneously determine item difficulty or location (i.e.the difficulty level of each item relative to other items in thescale), person ability (i.e. the ability level of each person rela-tive to other persons in the sample), and item-level fit statistics(degree of variation in the responses relative to the predicted

What this paper adds• This article provides a Rasch analysis of item-level measurement characteris-

tics of a combined FAQ ⁄ PODCI item set which exhibits better content cover-age and greater precision than either item set alone.

• Item groupings at similar difficulty levels were consistent with the mean per-son abilities of subgroups based on FAQ-WL, GDI, and GMFCS level.

• Clinically meaningful integration of self-report measures (FAQ ⁄ PODCI), clinicalscales (GMFCS), and objective (GDI) assessments are described.

444 Developmental Medicine & Child Neurology 2012, 54: 443–450

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responses) for the combined FAQ-22 ⁄ PODCI TBM ⁄ SPFitem set. The Rasch model uses a log odds units (logit) scale,which is linear and additive. Logit distances describe the rela-tive performance on adjacent categories of the response scale.For our Likert scale, there is a point on the latent trait of phys-ical functioning at which ‘some difficulty’ and ‘much difficulty’are equally likely to be observed. So, on a logit scale at a point1.4 logits higher, ‘much difficulty’ is likely to be observed eighttimes for every two times that ‘some difficulty’ is observed.Precision (standard error) of the estimated person ability usingthe PODCI TBM ⁄ SPF items alone, the FAQ-22 items alone,and the combined set of FAQ-22 ⁄ PODCI TBM ⁄ SPF item setwas calculated based on the assumption that all items werecompleted.

All children were subsequently grouped by their FAQ-WL.Children with CP were also separately grouped by theirGMFCS level. In each of the subgroups for the FAQ-WL andGMFCS level, the mean Rasch-based person ability scorefrom the combined FAQ-22 ⁄ PODCI TBM ⁄ SPF item set wasdetermined. The differences between mean person abilityscores of the FAQ-WL and GMFCS subgroups were testedusing analysis of variance (ANOVA; p < 0.05) with least signifi-cant difference post hoc testing, correcting for multiple com-parisons if the main effect of the factor (FAQ-WL or GMFCSlevel) was significant. These resultant mean and related 95%confidence intervals were then compared with the item diffi-culty statistics from Rasch analysis to determine the corre-sponding sets of items that individuals at each GMFCS leveland FAQ-WL could be expected to perform with a 50%probability.

Pearson’s correlations were calculated between the GDIand person ability measures. The GDI was also used to groupchildren. The continuous GDI scores, ranging from 42 to116, were transformed to a discrete measure by creating five1-SD bins for GDI scores from 50 to 100 (50.1–60, 60.1–70,etc.). Those with GDI scores below 50 were grouped togetherand those with GDI scores above 100 were grouped together.The differences in mean person ability scores among GDIbins was tested using ANOVA (p < 0.05) with least significantdifference post hoc testing if the main effect of the factor(GDI bin) was significant.

RESULTSNine hundred thirty-five children and adolescents had gaitanalysis during the specified time frame. Of those 935, 485who had first-time gait analysis met the criteria for inclusion.Two hundred and eighty-nine children had a diagnosis of CP(104 GMFCS level I, 97 level II, 69 level III, 19 level IV) and196 children had other neurological or musculoskeletal diag-noses (73 orthopedic, 39 neuromuscular, 30 joint disorder, 17acquired brain injury, 11 genetic, 26 miscellaneous). Mean agewas 9 years 10 months (SD 3y 10mo). Demographic data aresummarized in Table I.

Exploratory and confirmatory factor analysis of the com-bined FAQ-22 ⁄ PODCI TBM ⁄ SPF item set indicated a suffi-ciently unidimensional underlying construct as only twofactors explained more than 5% of the variance. The ratio of

these two factors was greater than 12:1, indicating dominanceof the single factor. Consistently high communalities (range0.666–0.904) indicated that approximately 80% of the com-mon variance is represented by a single latent factor. Themodel goodness of fit statistics demonstrated adequate one-factor model fit (standardized root mean square resid-ual=0.071; Tucker–Lewis Index=0.976; Confirmatory FitIndex=0.979). Data met the statistical assumption of monoto-nicity necessary for subsequent Rasch analysis. Local depen-dence in 26 of 535 item pairings was noted, but the itemsretained. The item fit statistics for the combined item set areshown in Table SI (supporting information published online).

The resultant item person map showing the relationship ofthe combined set of item difficulties to the distribution of per-son abilities in the sample is provided in Figure 1. Item diffi-culties ranged from easiest (‘sit in a regular chair withoutholding on’ at )3.1 logits) to hardest (‘ice skating or rollerskating’ at 2.8 logits; Fig. 1 and Table II). Rasch analyses dem-onstrated adequate fit of all items except one (‘ride a three-wheel bike [or a two-wheel bike with training wheels]’) whichwas retained in the analyses. No floor or ceiling effects werenoted. The range of item difficulties closely matched the rangeof person abilities, with 35 of 36 skills (97%) falling within2 SDs of the mean person ability (Fig. 1).

The Rasch-derived person item map shown in parallel withmean (standard error) participant groupings based on FAQ-WL and GDI for all children and GMFCS level for those withCP is found in Figure 2. This figure illustrates the relationshipbetween the ability level of the person and the relevant tasksthat this person is likely and unlikely to be able to accomplish.It also depicts the relationship between the FAQ-WL,GMFCS, and GDI with item difficulties.

Estimated person abilities based on the FAQ-22 ⁄ PODCITBM ⁄ SPF item set exhibited strong correlation with classifi-cation by FAQ-WL (Spearman’s rho = 0.739; p < 0.001) andGMFCS level (Spearman’s rho = )0.777; p < 0.001). There wasa significant difference in mean estimated person ability whengrouped by FAQ-WL classifications 6 to 10. Post hoc testing

Table I: Demographics and breakdown of available data by diagnosiscategory

Overall(n=485)

Cerebral palsy(n=289)

Other(n=196)

Sex, M ⁄ F 273 ⁄ 212 172 ⁄ 117 101 ⁄ 95Mean age (SD), y 9.9 (3.8) 9.1 (3.8) 11.1 (3.7)GMFCS (CP only) level

I – 104 –II – 97 –III – 69 –IV – 19 –

FAQ, n 479 285 194PODCI, n 465 277 188GDI, n 480 284 196

Age range for all children is 3 to 19 years. Differences in total numbersrepresent missing data values for some variables. n, number totals;GMFCS, Gross Motor Function Classification System; FAQ, GilletteFunctional Assessment Questionnaire; PODCI, Pediatric Outcome DataCollection Instrument; GDI, Gait Deviation Index.

Rasch Analysis of the FAQ ⁄ PODCI Jean L Stout et al. 445

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Logits

6 ## +

+

+

+

+

+

+

+

+

+

+

+

.##

.#

.##

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.###

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.#########

.######

.######

.####################.#######

.########.######

.######.########

.####

#######.###

###.#.#

#.

.

.

.

.

.###########

######

##########

.#####

.# T

T

S

S

M

M

S

S

T

T

#

.#

.

#

5

4

3

2

1

0

–1

–2

–3

–4

–5(less able) (less difficult)

PODCI29

PODCI31

PODCI28

PODCI7

FAQ1

FAQ16

FAQ10FAQ12

FAQ22

FAQ13

FAQ19FAQ11

FAQ21

FAQ14

FAQ7FAQ4

FAQ17 FAQ18 FAQ20FAQ8 FAQ9FAQ15 FAQ5

FAQ3

PODCI30

PODCI24PODCI21

PODCI19PODCI20

PODCI33

PODCI22

PODCI25

PODCI23PODCI18FAQ6FAQ2

Persons(more able) (more difficult)

– –MAP Items

Figure 1: Rasch Item Person Map. The frequency distribution of the sample by person ability (left) and item difficulty (right) is demonstrated on a single diffi-culty continuum. The vertical scale (logits) is an interval scale which represents the relative difficulty of lower extremity function, with lower numbers repre-senting easier skills (less person ability) and higher numbers representing more difficult skills (more person ability). Each `#' represents three children andeach `.' represents one child. Items in the right hand column include the Gillette Functional Assessment Questionnaire (FAQ) items (FAQ1:22) and PediatricOutcome Data Collection Instrument (PODCI) transfers and basic mobility ⁄ sports and physical function (TBM ⁄ SPF) items (PODCI*). Please refer to Table IIfor item descriptions. Ideally, these two columns (item responses and person ability) should appear similar, with the distribution of possible item responsesand person skill ability spread similarly across the difficulty scale. Distribution shows that most items and abilities surround the mean and 1 SD. M, mean; S,one SD; T, 2 SD of person ability (left) or item difficulty (right).

446 Developmental Medicine & Child Neurology 2012, 54: 443–450

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indicated that each estimated mean person ability for eachFAQ-WL 6 to 10 was statistically different from all otherFAQ-WLs (ANOVA; p < 0.05). There was a significant differ-ence in estimated person ability when grouped by GMFCSlevel (ANOVA; p < 0.05). The mean person ability for eachGMFCS level was statistically different from all otherGMFCS levels.

Similarly, the GDI exhibited a good correlation with esti-mated person abilities based on the FAQ-22 ⁄ PODCITBM ⁄ SPF item set (Pearson’s rank correlation coeffi-cient = 0.643; p < 0.001). As a continuous variable, each GDIscore has a broad range of abilities possible, and for each esti-mated person ability score there is a broad range of GDIscores possible (r2=0.42). When the person ability scores weregrouped into GDI SD bins, there were significant differencesin average ability score between the bins (ANOVA; p < 0.05).Post hoc testing revealed that Rasch-derived person scores foreach group by GDI 10-point bin was statistically different(p < 0.05) from all others except for GDI 50 to 60 with GDI60 to 70.

Precision of the combined FAQ-22 ⁄ PODCI TBM ⁄ SPFitem set was assessed by calculating the standard error for eachability score. The standard error of the model for each scorealong the ability spectrum is shown in Figure S1 (supportinginformation published online). At the high and low end ofscoring where there are few items that measure or provideinformation at these ability levels and few people with thoselevels of ability, the standard errors are, as expected, higher.Precision is best (standard errors are lowest) in the middle ofthe ability scale, where many tasks target that ability level andmany respondents have their ability. The combined item setmeasures a greater range of person abilities (content coverage)with better precision than either item set alone.

DISCUSSIONThe item difficulties derived from the Rasch analysis in thisstudy resulted in an interval-level measurement scale whichenables direct comparison of item difficulties between items

Table II: The 22 FAQ skill items and 14 PODCI TBM ⁄ SPF Items are shownin order of difficulty on an interval scale

Item no. DescriptionMeasure(logits)

GDI ‡ 100.1; CI: 2.46, 3.86 3.16FAQ Walking Level 10 Mean Ability;95% CI: 2.45, 3.06

2.76

F21 Ice skate or roller skate 2.71F11 Jump rope 2.30

GDI 90.1–100.0; CI: 1.83, 2.67 2.25F19 Ride 2 wheel bike (without

training wheels)2.02

GDI 80.1–90.0; CI:1.54,2.08 1.81F13 Hop on right foot 1.66F14 Hop on left foot 1.65

GMFCS Level I Mean Ability;95% CI:1.36,1.82

1.59

P22 Walk more than a mile 1.55FAQ Walking Level 9 Mean Ability;95% CI:1.01, 1.36

1.18

F04 Walk up and down stairs withoutusing the railing

0.92

F07 Runs well including around a cornerwith good control

0.84

GDI 70.1–80.0; CI:0.52,0.99 0.76F22 Ride an escalator, can step

on ⁄ off without help0.72

P20 Climb three flights of stairs 0.61F12 Jumps off a single step independently 0.43P19 Bicycle or tricycle 0.42

FAQ Walking Level 8 Mean Ability;95% CI:0.13, 0.52

0.32

F10 Can get on and off a bus byhim ⁄ herself

0.25

F02 Walk carrying a fragile object orglass of liquid

0.24

P18 Run short distances 0.24GMFCS Level II Mean Ability;95% CI:0.04, 0.44

0.24

P23 Walk three blocks 0.21F06 Runs 0.19P25 Get on and off the bus )0.13F18 Kick a ball with left foot )0.19F20 Ride 3 wheel bike (or 2 wheel bike

with training wheels))0.19

F17 Kick a ball with right foot )0.25F16 Step over an object, left foot first )0.29F15 Step over an object, right foot first )0.30

FAQ Walking Level 7 Mean Ability;95% CI: )0.73, 0.00

)0.37

F08 Can take steps backwards )0.39GDI 60.1–70.0; CI: )0.63, )0.18 )0.40GDI 50.1–60.0; CI: )0.64, )0.03 )0.41

F05 Steps up and down curb independently )0.41F09 Can maneuver in tight areas )0.42P33 Bend over from standing; pick

something off floor)0.72

P21 Climb one flight of stairs )0.77F01 Walk carrying an object )0.82F03 Walk up and down stairs

using the railing)0.90

GMFCS Level III Mean Ability;95% CI: )1.16, )0.72

)0.94

FAQ Walking Level 6 Mean Ability;95% CI: )1.30, )0.63

)0.97

P24 Walk one block )0.98P7 Put on coat )1.18

GDI <=50; 95% CI: )2.06, )0.81 )1.43FAQ Walking Level £5 Mean Ability;95% CI: )1.93, )1.01

)1.47

P30 Get on and off a toilet or chair )1.73

Table II: Continued

Item no. DescriptionMeasure(logits)

P28 Stand while washing handsand face at a sink

)1.88

GMFCS Level IV Mean Ability;95% CI: )2.77, )1.09

)1.93

P31 Get in and out of bed )2.23P29 Sit in a regular chair without holding on )3.13

F, FAQ-22 item; P, PODCI item. Measure ‘logits’ represents a non-dimensional level of difficulty. Higher ‘measure’ scores represent moredifficult tasks. Mean and 95% confidence interval of the average abilitylevels by GMFCS (bold), GDI bin (italic), and FAQ Walking Level(shadow pink) are shown. Average ability represents a 50% probabilityof successfully achieving a skill of the same level. Probability ofsuccess for a given level of person ability or classification grouping ishigher for items of lesser difficulty and lower for items of higherdifficulty. FAQ Walking Level £5 N=30 (14 FAQ-WL 5; 12 FAQ-WL 4; 2FAQ-WL 3; 2 FAQ-WL 2).

Rasch Analysis of the FAQ ⁄ PODCI Jean L Stout et al. 447

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from two different instruments of physical functioning. Bothmeasure a blend of ICF activity and participation qualifiers, sothe resultant represents not a single ICF aspect but a more gen-eral construct of physical functioning. The resultant calibrationof items from both instruments collected on the same sample(common people) provides a means to relate scores from theindividual measures (FAQ-22 and PODCI TBM ⁄ SPF) to eachother as well as to scores derived from the combined set. Inaddition, interpretation is now enhanced as the magnitude ofdifficulty between skills and person abilities is established onone common continuous interval scale. Individuals with Raschperson ability scores at a given level have a 50% probability ofsuccessfully completing skills at that same level of itemdifficulty. The improved precision and content coverage of thecombined FAQ-22 ⁄ PODCI TBM ⁄ SPF item set suggests thatthe use of both tools together may be an improved measure ofphysical functioning compared with using either instrument

alone. This reflects both the increased number of items in thecombined set and the distribution of items along the scale.Additional work to refine the set of items would be useful. Itemswith local dependence should be divided between different, butstill directly comparable, instrument versions.

When the individuals in the sample are grouped by FAQ-WL, GMFCS level, or GDI SD bin, their classification levelcan be related to groups of items that fall within the confidenceband of the group. For example, the relationship between FAQ-WL 8 and FAQ-22 skills ‘runs’ and ‘jump off a single step’ isnow established. Individuals’ estimated abilities can be associ-ated with the likelihood of their successful performance of agiven skill or set of skills. It broadens the scope of understandingof function beyond the interpretation of each tool or systemindividually, and establishes the relationship between item diffi-culties and person abilities. The information is specific enoughto be of practical use to clinicians, children, and families. For

–4.00

Easiest items

least able people

Hardest itemsmost able people

FAQ skill set

FAQ walking level

GMFCS level

PODCI items

GDI

Sit in

a re

gular

chair

Get in

and

out

of b

ed

Get o

n an

d of

f a to

ilet o

r cha

ir

Walk

1 b

lock

Put o

n co

at

Climb

1 flig

ht fo

stair

s

Bend

over

; pick

from

floor

Get o

n an

d of

f the

bus

Walk

3 b

locks

Run sh

ort d

istan

ces

Bicycle

or t

ricyc

le

Climb

3 flig

hts o

f sta

irs

Walk

a m

ile

Walk

up/

down

stairs

usin

g ra

iling

FAQ ≤≤5

GMFCS 4

GMFCS 3

GMFCS 2

GMFCS 1

GDI ≤50

GDI 50–

60

GDI 60–

70

GDI 70–

80

GDI 80–

90

GDI 90–

100

GDI >10

0

FAQ 6

FAQ 7

FAQ 8

FAQ 9

FAQ 10

Walk

carry

ing o

bject

Man

euve

r in

tight

are

as

Step

up/d

own

curb

Step

back

wards

Step

over

obje

ct

Ride 3

whe

el bik

e

Kick a

ball

Runs

Get o

n/of

f a b

us

Walk

carry

ing a

frag

ile o

bject

Jum

p of

f a si

ngle

step

Ride a

n es

calat

or

Runs w

ell in

cludin

g ar

ound

a co

rner

Walk

up/

down

stairs

with

out r

ailing

Hop o

n R/L

foot

Ride 2

whe

el bik

e

Jum

p ro

pe

Ice sk

ate

or ro

ller s

kate

Stand

was

hing

hand

s at s

ink

–3.00 –2.00 –1.00 0.00

Person ability or item difficulty (logits)

1.00 2.00 3.00 4.00

Figure 2: Rasch-derived person item map and functional classification subgroups. Item level difficulty scores for the combined Gillette Functional Assess-ment Questionnaire (FAQ) FAQ-22 ⁄ Pediatric Outcome Data Collection Instrument (PODCI) transfers and basic mobility ⁄ sports and physical function(TBM ⁄ SPF) item set are shown in parallel with mean (standard error) person ability participant groupings based on FAQ-WL 5 to 10 and 1 SD Gait DeviationIndex (GDI) bins for all individuals, and Gross Motor Function Classification System (GMFCS) levels I to IV for children with cerebral palsy. The likelihood ofan individual being able to successfully perform specific skills is demonstrated. An individual at a given ability level will have a 50% chance of successfullyperforming a skill of that same difficulty level. For example, a child with a GMFCS level II classification has a 50% probability of being able to run shortdistances and a 50% probability of being able to walk carrying a fragile object. The same child has approximately a 12.5% probability of being able to walkup ⁄ down stairs without a railing because the skill is almost four times as difficult based on the logit scale. The FAQ-22 and PODCI TBM ⁄ SPF items areseparated only to more clearly identify each. The vertical dashed lines from the PODCI TBM ⁄ SPF items to the FAQ-22 items depict where they are locatedif presented as a single item set. The person ability or item difficulty is an interval scale.

448 Developmental Medicine & Child Neurology 2012, 54: 443–450

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example, when a child who walks at a FAQ-WL 8 and is able torun describes the difficulty encountered when attempting toplay hop-scotch or to skip with friends, the clinician now has atool to demonstrate that the ability to hop is more difficult thanthe ability to run. The same child, however, should be expectedto have the ability to ‘jump off a single step’ as it is within therange of item difficulty of the person ability estimate.

This study produced a model that matches clinical impres-sion of differences in skill level based on a GMFCS level. Forexample, the level of difficulty assigned to the ability to ‘walkup ⁄ down stairs without a railing’, a common skill used to dif-ferentiate between GMFCS levels I and II, clearly fallsbetween the two GMFCS levels on the difficulty scale.Another example, the ability to ‘hop on the right or left foot’,is associated with GMFCS I. The FAQ-22 skill set (designedto be a set of skills more advanced than walking) is associatedwith GMFCS levels I to III. Specifically, all FAQ-22 itemshad an estimated difficulty higher than the PODCI item ‘walkone block’, which has an estimated difficulty of )0.98. PODCIskills ‘get in ⁄ out of bed’ and ‘get on ⁄ off a toilet or chair’ arewithin a level of difficulty assigned to GMFCS IV. Across alllevels, the level of difficulty assigned to skills appears to beconsistent with clinical impression.

Understanding each perspective of function (proxy-reportinstruments, classification systems, and GDI) in the context ofthe others provides the clinician with a more complete inte-grated context for interpretation. Although previous reportshave demonstrated that measures of gait pathology such as theGDI or the Gait Profile Score distinguish between each pairof community walking levels on the FAQ,27,30 how they relatein difficulty has not been previously established. This can pro-vide direction for therapies, as well as counseling for familiesregarding expectations of their child’s abilities. It also canidentify mismatches in reported function.

A limitation of this study is that item misfit and responsedependency were found within our item set, but were notaccounted for within the study. The sample size impact on in-fit and outfit statistics may also be a potential limitation. A rec-ommendation for further work would be to investigate theimpact of this misfit and response dependency upon the scal-ing characteristics of the grouped item set.

The retrospective nature of our study limited the items andinstruments to those that were available on a large commonparticipant sample. Therefore, we focused our analyses on aversion of the FAQ-22 and a subset of the PODCI(TBM ⁄ SPF). The subset of PODCI items selected for analysesrelied on the same five-point Likert difficulty scale as the FAQ-22 in order to maintain consistency of item structure for theRasch analysis. The excluded items were frequency of personal

assistance or use of assistive device questions (sitting ⁄ standing[TBM] and walking ⁄ climbing [SPF]) not associated with anyparticular skill. In addition, the PODCI SPF items concerningparticipation in recreational outdoor activities, pick-up gamesor sports, competitive level sports, and gym ⁄ recess also wereexcluded as the structure of the questions included a condi-tional response that is not consistent with other questions. Wewould expect that if these items were included, the upper rangeof the PODCI item coverage would be extended toward themore difficult end, as found for the FAQ-22 items.

Another potential limitation is the inclusion of only childrenwho were ambulatory and referred for gait analysis. Hence,our results should be interpreted very cautiously in non-ambu-lant children with lower skill levels than our study sample andare not an exhaustive query of functional skills, which areimportant supplements to locomotion. Given that the scope ofour work was on application of Rasch analyses to improve ourknowledge of the measurement properties of the combinedinstruments, we did not attempt to directly map the includeditems to specific ICF components and qualifiers. Future workusing a prospective longitudinal design will help to define reli-ability and responsiveness, including the minimum clinicallyimportant difference. Studies of changes in skill ability as aresult of intervention are also needed.

CONCLUSIONSThe combined FAQ-22 ⁄PODCI TBM ⁄ SPF item sets orderedusing Rasch analysis lays the foundation for a framework to linkoutcome tools. This study represents an initial attempt to relateperson ability and skill difficulty to functional classification andgait impairment. The association between the classificationscales and GDI and a specific cluster of items from the ordereditem set may help clinicians to better understand the relation-ship between each type of measure and potentially to guidetreatment with a level of confidence that specific skills are withinthe child’s capability. With continued efforts, the potential for aparadigm shift to an integrated view of how lower extremityfunction is conceptualized, measured, and reported is possible.

ACKNOWLEDGMENTSThis study was funded in part by an American Academy for Cerebral

Palsy and Developmental Medicine Planning Grant 2008. The

funding agency did not participate in any way in the conceptualiza-

tion, design, data collection, data analysis, manuscript preparation,

and ⁄ or publication decisions.

SUPPORTING INFORMATIONSupporting information may be found in the online version of this

article.

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