Validation of the work ability index\u2014single item and the pain disability index\u2014work item in patients with chronic low back pain

Imke Boekel,Henrica R Schiphorst Preuper,Alisa L Dutmer,Michiel F Reneman

doi:10.1007/s00586-022-07109-x

Imke Boekel, Henrica R Schiphorst Preuper + Show 2 more

Open Access

https://doi.org/10.1007/s00586-022-07109-x

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Abstract

PurposeA cross-sectional and longitudinal study was conducted to analyse construct validity, responsiveness, and Minimal Clinically Important Change (MCIC) in the Work Ability Score (WAS) and Pain Disability Index Work item (PDI-W) in patients with Chronic Low Back Pain (CLBP).MethodConstruct validity was assessed by testing predefined hypotheses. Responsiveness and MCIC were measured with an anchor-based method. The area under the receiver Operating Characteristic Curve (AUC) and the optimal cut-off point were calculated. Smallest Detectable Change (SDC) was calculated to determine measurement error.ResultsIn total, 1502 patients (age 18–65 years) with CLBP were included. For validity of the WAS and PDI-W, respectively, seven and six out of 10 hypotheses were not rejected. The WAS (n = 355) was responsive to change with an AUC of 0.70. MCIC was 1.5 point, SDCindividual 4.9, and SDCgroup 0.3. MCICs were 4.5, 1.5, and − 0.5 points for, respectively, low, middle, and high scoring baseline groups. The PDI-W (n = 297) was responsive to change with an AUC of 0.80. MCIC was − 2.5 points, SDCindividual 5.2, and SDCgroup 0.3. MCICs were − 0.5, − 2.5, and − 4.5 points for, respectively, low, middle, and high scoring baseline groups.ConclusionConstruct validity of the WAS and PDI-W was insufficient in this patient sample. The WAS and PDI-W are responsive to change. On average, improvements of 1.5 point (WAS) and − 2.5 points (PDI-W) were interpreted as clinically important. However, MCICs are also baseline dependent. Due to a risk of measurement error, at the individual level change scores should be interpreted with caution.

Highlights

The prevalence of disability due to Low Back Pain (LBP) increases from the third decade of life on, peaking between the age of 35 and 55 years [1]
Patients digitally filled out a set of questionnaires at baseline (T0) and 6 months follow-up (T1), including the Work Ability Score (WAS), Pain Disability Index Work item (PDI-W), a modified version of the short Copenhagen Psychosocial Questionnaire (COPSOQ II), the EuroQol-5D (EQ5D), the National Institutes of Health (NIH) Impact Stratification, and a Global Perceived Effect (GPE) scale
Clinically important change could not be distinguished from measurement error, since Minimal Clinically Important Change (MCIC) were smaller than Smallest Detectable Change (SDC) values

Summary

Introduction

The prevalence of disability due to Low Back Pain (LBP) increases from the third decade of life on, peaking between the age of 35 and 55 years [1]. LBP causes a large number of absenteeism and work productivity losses [2]. This makes LBP the most common health problem in the European. Higher work ability is associated with less disability and pain, and higher quality of life [6]. The Work Ability Index (WAI) was developed as a measure for selfreported work ability. The Work Ability Score (WAS) is an item of the WAI and compares current work ability with lifetime best [7]. It is an acceptable brief alternative for the WAI in determining work ability [8].

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