Work Ability Index

Adult Workers: (Gonzalez-Dominguez et al., 2024; n = 233, mean age 41.55 (7.51), male = 206 (88.4%), Spanish translation of WAI for adult workers at a multinational aeronautical company)

• SEM (calculated) for overall WAI = 2.76

Adult Workers: (Gonzalez-Dominguez et al., 2024)

• MDC (calculated) for overall WAI = 7.65

Adult Workers: (Jääskeläinen et al., 2016; n = 5251; mean age = 50.4 (3.6) years, female = 2957 (56.3%), sample of Finnish municipal employees)

• Optimal cut-off points based on the Youden index: for men = 24.0 (sensitivity 58.5% and specificity 67.15); for women = 23.9 (sensitivity 75.3% and specificity 71.3%)
• ≤ 27 indicates poor WAI (sensitivity 49.2%; specificity 82.9%)
• ≥ 36 indicates moderate WAI (sensitivity 84.2%; specificity 44.3%)

Adult Workers: (De Zwart et al., 2002; n = 97, mean age = 51 years (age range = 40-60 years), male = 96 (99%), test-retest interval = 4 weeks, employees in Dutch construction industry) 

• Acceptable: No significant difference in the mean WAI score at the group level between test (mean WAI score = 40.4 (6.1)) and retest (39.9 (6.4)).
  • 25% of subjects (24 out of 97) reported the exact same score on test and retest. 
  • 95% of the individual differences between the two test scores were found to be < 6.86 points (2 x SD)

Adult Workers: (Mateo Rodriguez et al., 2021; n = 1184, mean age = 56.5 (5.7), female = 71.1%, workers at six Spanish health care centers, Spanish translation of WAI)

• Excellent: Cronbach’s alpha (n = 1062) = 0.81

   

Adult Workers: (da Silva Jr et al., 2011; n = 1436, mean age = 40 (12.7) years, age range = 16-70, female = 87.3%, nursing workers in Brazil, Brazilian Portuguese translation of WAI)

• Excellent: Cronbach’s alpha = 0.8; McDonald’s omega (ω) = 0.87

Adult Workers: (Gonzalez-Dominguez, 2024)

• Adequate: Cronbach’s alpha = 0.74

Predictive validity:

Adult Workers: (Jääskeläinen et al., 2016)

• Poor ability of WAI scores to predict disability retirement among men from 1981 to 1985 (AUC = 0.68 (95% CI 0.64-0.72)
• Adequate ability of WAI scores to predict disability retirement among women from 1981 to 1985 (AUC = 0.79 (CI 0.75-0.82)

Adult Workers: (Lundin et al., 2017, n = 1786, mean age = 42.7 years, age range = 25-60 years, from stratified random national sample of 25 to 75 year-olds living in Sweden in 2000 in the Work, Health, & Retirement Study)

• Acceptable predictive validity for long-term sickness absence (LTSA; ≥ 90 consecutive days) over 4 years — AUC = 0.79 (95% CI 0.76–0.82)
• Three items may be suitable proxies of the full WAI in predicting LTSA for public health surveys: I) Current work ability compared to lifetime best (AUC = 0.72 (95% CI 0.69–0.76)); III) Number of current illness diagnosed by a physician (AUC = 0.71 (95% CI 0.68–0.74)); and IV) Estimated work impairment due to diseases (AUC = 0.76 (95% CI 0.73–0.80))

Adult Workers: (Mateo Rodrigeuz, 2021)

• Significant ability of WAI scores to predict scores on the SF-12 was shown via a linear regression model (R² = 63.2, F = 1204.85, p < 0.001)

Convergent validity:

Adult Workers: (Gonzalez-Dominguez, 2024)

• Adequate correlation between overall WAI and workers’ self-assessment of health status (r_s = 0.48, p < 0.001)

Adult Workers: (Mateo Rodrigeuz, 2021)

• Principal components analysis suggested the presence of one single factor, with this one-factor model explaining 50.49% of overall accumulated variance. The one-factor model showed acceptable fit in terms of the comparative fit index (CFI) (0.92) and normalized fit index (NFI) (0.92), but the chi-square index (p = 0.000), Tucker-Lewis index (TLI) (0.836), and RMSEA (0.111) values were not acceptable.
• A two-factor model outperformed the one-factor model (X² = 59.52, CFI = 0.98, TLI = 0.96, RMSEA = 0.06). Factor 1, “subjectively estimated work ability,” incorporated items 3, 4, and 5; and factor 2, “ill-health-related ability,” incorporated items 1, 2, 6, and 7.

Discriminant validity:

Adult Workers: (Gonzalez-Dominguez, 2024)

• Significant ability of the WAI to discriminate between younger (≤ 44 years of age, mean WAI score = 43.3 (5.44)) and older (≥ 45 years of age, mean WAI score = 41.6 (5.44)) workers (U = 4226.00, p = 0.005)

Adult Workers: (Mateo Rodrigeuz, 2021)

• Adequate ability of the WAI to discriminate between “good” and “poor” groups based on median self-reported health scores (AUC = 0.87 (95% CI = 0.85-0.90))

• Mean 4-year change in WAI total score = -2.8 points for both men and women