Work Ability Score (WAS), single-item
Identity
Version: Single item: current work ability rated against lifetime best on a 0 to 10 numeric scale. It is item 1 (the first dimension) of the Work Ability Index; also termed the WAI single-item or WAI-1.
Structure: 1 item (0 to 10 scale)
Original citation: As item 1 of the WAI: Tuomi K, Ilmarinen J, Jahkola A, Katajarinne L, Tulkki A. Work Ability Index, FIOH, Helsinki (2nd revised edn 1998). The single-item usage was formalised and named 'Work Ability score' by El Fassi 2013.
Steward / publisher: Finnish Institute of Occupational Health (FIOH / Tyoterveyslaitos), as originator of the parent WAI; German distribution via WAI-Netzwerk / BAuA.
Constructs claimed
Global self-assessed current work ability relative to lifetime best. Intended as an efficient proxy for overall work ability suitable for surveys and repeated monitoring where the full WAI is impractical.
Evidence
Structural validity Not applicable (category difference)untestedevidence form: canonical
direct category error for a single-item measure.
Not applicable: a single item has no internal factor structure to evaluate.
Convergent and discriminant validity Moderatecontestedevidence form: canonical
indirect evidence from Belgian/Luxembourg, Swedish, Iranian, Danish and Dutch samples; weaker in clinical populations.
The WAS converges strongly with the full WAI, its parent instrument. El Fassi and colleagues reported a Spearman correlation of rs=0.63 between WAS and total WAI in 12,389 workers (El Fassi 2013), and Ahlstrom and colleagues found a very strong association between the single item and the full WAI in women on long-term sick leave (Ahlstrom 2010). The WAS explained about 44 per cent of the variance in WHOQOL-BREF quality of life, almost identical to the 46 per cent from the full WAI (Mokarami 2021). Face validity is supported by a moderate correlation with objectively measured heart-rate reserve in male blue-collar workers (R=-0.33, p=0.005), though not in females (Gupta 2014). In clinical samples convergent validity is weaker: only moderate positive construct validity in a Brazilian online study (Pucci 2024), and in chronic low back pain only 7 of 10 (WAS) predefined hypotheses were met, judged insufficient (Boekel 2022).
Sub-grades (evidence differs by subgroup):
- {"subgroup": "vs full WAI in occupational samples", "grade": "Moderate", "note": "consistent moderate-to-strong convergence (rs around 0.63)"}
- {"subgroup": "clinical pain/disability samples", "grade": "Low", "note": "construct-validity hypotheses only partly met"}
Criterion validity: reference standard Moderatecontestedevidence form: canonical
indirect the WAS is validated chiefly against the full WAI as the reference, in non-UK occupational cohorts.
The natural reference standard for the WAS is the full multi-item WAI, against which it converges moderately (rs=0.63) (El Fassi 2013) and which it approaches in explained variance for health-related quality of life (Mokarami 2021). Against genuine diagnostic reference standards there is no evidence, and none exists for work ability generally. Where head-to-head against the WAI for risk stratification, the single item is inferior: it poorly discriminated disability-pension risk (AUC 0.67) versus the full WAI (AUC 0.78) and showed miscalibration in male construction workers (Roelen 2014).
Criterion validity: organisational Moderatewell-establishedevidence form: canonical
indirect for the UK (Finnish, Swedish, Dutch cohorts) but direct against real work outcomes; note the single item is consistently a weaker discriminator than the full index.
The WAS predicts work outcomes but generally less well than the full WAI. In 11,131 Finnish employees a poor WAS carried a hazard ratio of 9.84 (95% CI 6.68 to 14.49) for register-based disability pension and an incidence rate ratio of 3.08 (95% CI 2.19 to 4.32) for accumulated long-term sickness absence days versus good/excellent WAS (Kinnunen 2017). In Finnish municipal employees poor versus good/excellent WAS gave a disability-pension hazard ratio of 3.4 (95% CI 3.0 to 3.8), lower than the full WAI's 5.0 (Jaaskelainen 2016). Directly compared in 11,537 male construction workers, the WAS was associated with disability pension (OR 0.72 per point, 95% CI 0.66 to 0.78) but discriminated poorly (AUC 0.67) and was miscalibrated, leading the authors to recommend the full WAI for screening (Roelen 2014). Among women on long-term sick leave the single item and full WAI showed similar predictive value for degree of sick leave (Ahlstrom 2010), and the single 'current work ability vs lifetime best' item was one of three WAI items exceeding AUC 0.70 for long-term sickness absence in the Swedish general population (Lundin 2017). WAI-1 and the two-item WAI-2 predicted burnout and intention to leave the profession in the large European NEXT nursing study (Ebener 2019).
Internal consistency Not applicable (category difference)untestedevidence form: canonical
direct category error for a single-item measure.
Not applicable: internal consistency (Cronbach's alpha / omega) cannot be computed for a single item.
Test-retest reliability Lowcontested
indirect small clinical-rehabilitation samples and one general-worker sample; no UK data.
| Coefficient | Type | Interval | Sample | Population | Evidence form |
|---|---|---|---|---|---|
| 0.89 (95% CI 0.76 to 0.96) | ICC | 2 to 4 weeks | 21 (stable subgroup, after excluding 1 outlier) | Dutch vocational-rehabilitation patients with physical disability (spinal cord injury, acquired brain injury, neuromuscular disease) | canonical |
| 0.89 (95% CI 0.77 to 0.94) | ICC | admission retest within vocational rehabilitation | 34 | Dutch sick-listed workers with chronic musculoskeletal pain | canonical |
| 0.52 (general work ability, 0 to 10) | ICC | 7 days | 104 | Dutch workers (general working population) | derivative (general single-item work-ability appraisal, WAS-analogue) |
Test-retest reliability of the WAS is contested and interval/sample-dependent. Two vocational-rehabilitation studies report good ICCs around 0.89 (Stienstra 2021; van Dinter 2025), but both rest on very small stable subgroups (n=34 and n=21). A general-working-population study of a closely analogous single 0 to 10 general work-ability item found only moderate reliability (ICC 0.52 over 7 days) (van Schaaijk 2018). The single-item retest coefficient is therefore not uniformly high, and the strong clinical-sample ICCs should not be generalised to routine workplace surveillance.
Measurement invariance Not applicable (category difference)untestedevidence form: canonical
direct invariance testing is a category error for a single item in isolation.
No formal measurement-invariance analysis is possible or reported for the single-item WAS as a stand-alone measure; invariance is a multi-item concept. Cross-group score differences (for example by age or sex) are reported in WAI studies but do not constitute invariance evidence.
Responsiveness and MIC Lowthinevidence form: canonical
indirect responsiveness/MIC established only in clinical rehabilitation samples (chronic pain, low back pain), not UK workplace populations.
The WAS is responsive to change in clinical rehabilitation, with anchor-based minimal important change estimates. In sick-listed workers with chronic musculoskeletal pain the WAS was responsive (AUC 0.70) with a minimal clinically important change around 1.5 points and baseline-dependent MICs (Stienstra 2021). In chronic low back pain the WAS was responsive (AUC 0.70), MIC about 1.5 points, smallest detectable change about 4.9 points, though its construct validity in that sample was judged insufficient (Boekel 2022). The Brazilian online study likewise reported good-to-excellent test-retest and construct validity for the single item (Pucci 2024). Responsiveness evidence is thus concentrated in clinical populations.
Populations, languages and norms
As the first WAI item, the WAS inherits the WAI's wide language coverage and is used in occupational surveys (Finnish, Swedish, Dutch, Belgian/Luxembourg, Iranian, Brazilian) and increasingly in vocational rehabilitation. Because the 0 to 10 scale is intuitive it is popular for repeated monitoring. No dedicated UK norms were located in the latest review pass.
Criticisms and controversies
The central controversy is whether a single item can substitute for the full WAI. Evidence is mixed: the WAS converges moderately with the WAI and predicts disability pension and sickness absence, but it is a consistently weaker discriminator (for example AUC 0.67 vs 0.78 for disability pension) and can be miscalibrated, so several authors recommend the full index for individual-level screening while accepting the single item for population surveillance. Test-retest reliability is not uniformly high once general-worker (rather than clinical) samples are considered. Much of the strongest reliability and responsiveness evidence comes from clinical rehabilitation cohorts, which is indirect for routine workplace use.
References (14)
- Ahlstrom L, Grimby-Ekman A, Hagberg M, Dellve L (2010). The work ability index and single-item question: associations with sick leave, symptoms, and health--a prospective study of women on long-term sick leave. https://doi.org/10.5271/sjweh.2917
- El Fassi M, Bocquet V, Majery N, Lair M, Couffignal S, Mairiaux P (2013). Work ability assessment in a worker population: comparison and determinants of Work Ability Index and Work Ability score. https://doi.org/10.1186/1471-2458-13-305
- Gupta N, Jensen B, Søgaard K, Carneiro I, Christiansen C, Hanisch C, Holtermann A (2014). Face validity of the single work ability item: comparison with objectively measured heart rate reserve over several days. https://doi.org/10.3390/ijerph110505333
- Roelen C, van Rhenen W, Groothoff J, van der Klink J, Twisk J, Heymans M (2014). Work ability as prognostic risk marker of disability pension: single-item work ability score versus multi-item work ability index. https://doi.org/10.5271/sjweh.3428
- Jääskeläinen A, Kausto J, Seitsamo J, Ojajärvi A, Nygård C, Arjas E, Leino-Arjas P (2016). Work ability index and perceived work ability as predictors of disability pension: a prospective study among Finnish municipal employees. https://doi.org/10.5271/sjweh.3598
- Lundin A, Leijon O, Vaez M, Hallgren M, Torgén M (2017). Predictive validity of the Work Ability Index and its individual items in the general population. https://doi.org/10.1177/1403494817702759
- Kinnunen U, Nätti J (2017). Work ability score and future work ability as predictors of register-based disability pension and long-term sickness absence: A three-year follow-up study. https://doi.org/10.1177/1403494817745190
- van Schaaijk A, Nieuwenhuijsen K, Frings-Dresen M, Sluiter J (2018). Reproducibility of work ability and work functioning instruments. https://doi.org/10.1093/occmed/kqy010
- Ebener M, Hasselhorn H (2019). Validation of Short Measures of Work Ability for Research and Employee Surveys. https://doi.org/10.3390/ijerph16183386
- Mokarami H, Cousins R, Kalteh H (2021). Comparison of the work ability index and the work ability score for predicting health-related quality of life. https://doi.org/10.1007/s00420-021-01740-9
- Stienstra M, Edelaar M, Fritz B, Reneman M (2021). Measurement Properties of the Work Ability Score in Sick-Listed Workers with Chronic Musculoskeletal Pain. https://doi.org/10.1007/s10926-021-09982-7
- Boekel I, Dutmer A, Schiphorst Preuper H, Reneman M (2022). Validation of the work ability index-single item and the pain disability index-work item in patients with chronic low back pain. https://doi.org/10.1007/s00586-022-07109-x
- Pucci R, da Silva A, Padula R (2024). Factorial analysis of the Brazilian-Portuguese version of the Work Ability Index, reproducibility and validity of the single item and the short version for online application. https://doi.org/10.1016/j.bjpt.2024.101060
- van Dinter R, Jenks A, Roels E, Post M, Reneman M (2025). Test-Retest Reliability and Agreement of the Work Ability Index-Single Item in Persons With Physical Disabilities. https://doi.org/10.1016/j.apmr.2024.10.018
Record notes
Overall confidence: as a single-item proxy the WAS has well-established organisational predictive validity (Moderate, consistently weaker than the full WAI) and Moderate but contested convergence with its parent instrument; test-retest is Low/contested (good ICCs only in small clinical subgroups, moderate in general workers); responsiveness is Low and confined to clinical samples. Scale-level properties (internal consistency, structural validity, measurement invariance) are correctly Not-applicable rather than Absent per rule 4. All applicable grades are indirect for a UK working-adult audience because no UK validation or norms were located. The schema v0.2 single-item handling worked cleanly; the one nuance recorded honestly is that one retest coefficient (van Schaaijk) is a derivative general single-item work-ability appraisal rather than the exact WAI-1 wording, tagged as derivative evidence_form in the structured test-retest sub-object. Licence could not be verified against a primary steward page in the latest review pass because FIOH (ttl.fi) and BAuA (baua.de) returned server-side 403 blocks and the reachable WAI-Netzwerk portal does not state questionnaire terms; per rule 7 the licence is recorded as not verified in the latest review pass rather than asserted from literature.