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A direct comparison of the reliability and validity of patientcentred measures of atwork productivit

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Title: A direct comparison of the reliability and validity of patientcentred measures of atwork productivit


1
A direct comparison of the reliability and
validity of patient-centred measures of at-work
productivity loss in persons with inflammatory
and osteoarthritis.
  • Dorcas Beaton, BScOT, PhD
  • Scientist,
  • St Michaels Hospital and the Institute for Work
    Health
  • University of Toronto, Toronto, Ontario, Canada

2
Co-investigators
  • Claire Bombardier
  • Diane Lacaille
  • Monique Gignac
  • Anusha Govinda-Raj
  • Sherra Solway

3
Work
4
At work productivity loss
  • But what is happening at work?
  • Greatest portion of lost productivity costs due
    to arthritis gtgt absenteeism costs (Li, 2005)
  • Understudied, inconsistently measured.
  • Step 1 Measure it well
  • Aim economic ( cost) and impact on QOL state
    (state description)

5
Review of existing literature
  • 16 different scales
  • 5 direct comparisons
  • Different levels of work limitations (Lavigne,
    2003)
  • Low correlations between measures
  • Little information in arthritis

HLQ, Osterhaus (Lavigne, 2003)
WLQ25, WPSI (Ozminkowski, 2004)
Osterhaus, QQ (Brouwer, 1999)
WLQ25, SPS13 (Turpin, 2004)
QQ, HLQ (Meerding, 2005)
6
Objectives
  • To directly compare the measurement properties of
    five different scales in persons with IA and OA
  • Design
  • Cross sectional survey, n250 persons, 3 clinical
    sites
  • 130 OA, 120 RA
  • Working for pay in the past month
  • Able to complete questionnaire in english
  • Completed by either touch screen or paper
    (randomly assigned to each disease group)

7
Measures
  • WIS-RA - Work instability scale (Gillworth, 2003)
  • 23 items, one score, yes/no response,
    difficulties encountered
  • WLQ-25 (Work Limitations Questionnaire Lerner,
    2002)
  • 25 items, 4 domains, 5 response options, time in
    difficulty
  • WALS (Work Activity Limitations Scale, Gignac,
    2004)
  • 11 items, one domain, 4 response options,
    difficulty
  • EWPS (Endicott Work Productivity Scale) (1997)
  • 25 items, one domain, 5 response options,
    frequency
  • SPS-6 (Stanford Presenteeism Scale-6)(Koopman,
    2002)
  • 6 items, one domain, 5 response options, degree
    of agreement with limitation

8
Results
All
IA
OA
  • N 250 130 120
  • Age (mean (sd)) 50.4 (9.7) 54.0 (6.7) 46.2 (10.9)
  • Gender (F) 82.7 80.5 85.3
  • Duration 54.7 49.2 61.1
  • ( gt 5 yrs)
  • comorbidities 1.9 (1.1) 2.2 (1.1) 1.6 (0.9)
  • HAQ-DI 0.76 (0-2.25) 0.76 (.58) 0.76 (.56)

9
EWPS
21.5/100 (13.9)
WLQ-25
SPS-6
27.8/100 (18.7)
13.3/30 (5.1)
WALS
WIS
8.0/33 (5.1)
8.3/23 (6.4)
Note all scales transformed to 0-100, 100 more
limitation for graphs
10
Scores IA versus OA (pgt0.05)
Raw scale scores
11
Reliability Internal consistency
Cronbachs alpha or KR-20
12
Construct validity
  • Correlations with 5 global markers of work
    ability (expected gt 0.75)
  • Spearman rho 0.5-0.7, WIS was 0.8
  • Correlations slightly higher (0.1) in OA gt RA
  • Correlations between scales (expected gt 0.75)
  • Spearman rho 0.2 0.7
  • Median 0.5
  • Lower than expected
  • WLQ-PD scale consistently low (0.3)

13
Construct validity discrimination
Discrimination between those hindered (46) or
not hindered (54) at their work
Unpaired t-statistic (mean difference / se )
(All significant at plt0.05)
14
Arthritis consumer preference
RA OA
Preferred scale ( of sample)
Order in survey ?
15
Conclusion
  • Reliability okay (SPS, WLQ-25 problematic)
  • Validity lower, WIS ranked highest
  • Slight differences OA/RA should not be of
    concern.
  • More concerning
  • Different scales ? different things.
  • Problems with PD subscale WLQ ? reversed scale?
  • ? Need to use 2 scales match patient
    preference!
  • Economic analyses ? time
  • Outcome state ? difficulty

16
Future
  • Longitudinal construct validity
  • Responsiveness
  • Same cohort ? one year
  • Collaborations internationally
  • On agenda at OMERACT 9 (May 2008)
  • How to measure productivity loss
  • How to blend off-work, at-work outcomes
  • How to measure the contextual nature of work

17
Thank you
  • Acknowledgements
  • This study was funded by the Canadian Arthritis
    Network
  • Dr Beaton is supported by a New Investigators
    award from CIHR
  • OMERACT is supporting collaboration on work
    disability measurement
  • Thank you to the research staff, and the patients
    who participated in this study
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