CHAPTER 104: WORK ABILITY INDEX (WAI)
Description
The Work Ability Index (WAI) is a self-administered questionnaire designed to quantify an individual’s capacity for work, which is thought to occur as a result of the interaction of various determinants such as health, competence, and attitudes toward work, as well as the environment in which work takes place (Bethge, Radoschewski, & Gutenbrunner, 2012). Used as a predictive tool to identify workers at high risk for long-term sickness, absence, or disability as well as associated symptomology, the theoretical basis of the WAI is the stress/strain model, which emphasizes the important interplay of the individual and environmental factors on work ability (Bethge et al., 2012; Reeuwijk et al., 2015). The WAI has 10 items that comprise 7 dimensions and include such questions as, “Assuming that your work ability at its best has a value of 10 points how many points would you give your current work ability?” For each item a single score is obtained where the total score is a summation of all single item scores (range: 7 to 49), with higher scores indicating better work ability. Subject work ability can then be classified into 4 categories based on the total score as follows: poor (7 to 27 points), moderate (28 to 36 points), good (37 to 43 points), and excellent (44 to 49 points) (de Zwart, Frings-Dresen, & van Duivenbooden, 2002). The WAI can be completed in less than 10 minutes.
TABLE 104-1
ADAPTATION OF THE WORK ABILITY INDEX: FACTORS RELATED TO WORK SUCCESS
Adapted from Finnish Institute of Occupational Health. (2014). Multidimensional work ability model. Retrieved from www.ttl.fi/en/health/wai/multidimensional_work_ability_model/pages/default.aspx
Psychometrics
A study of 97 construction industry workers (14% management and administrative) with a mean age of 51 years (range 40 to 60 years old) established reliability using test–retest data from a 4-week interval and found no significant differences in the mean WAI score at the group level between measurements (40.4 vs 39.9) (de Zwart et al., 2002). Exactly the same score on both measurements were reported by 25% of the subjects and 95% of the individual differences between measurements were found to be within < 7 points of each other (de Zwart et al., 2002). The study also found that the percentage of observed agreement for the classification of subjects into 1 of the 4 WAI categories on both measurements was 66% (de Zwart et al., 2002). Results also showed that a decrease in work ability was more common than an improvement (de Zwart et al., 2002). A study by da Silva Junior, Vasconcelos, Griep, and Rotenberg (2011) using results of 1436 nurse questionnaires found the Cronbach’s alpha to be α = 0.80, suggesting that all items correlated well, whereas a factorial analyses indicated a two-dimensional structure of perception of work ability/mental resources and diseases and health restrictions. A later study by Fassi et al. (2013) of 12,839 40- to 65-year-old subjects established that the convergent validity between WAI and the work ability score (the first item of the WAI) was statistically significant at r = 0.63. The study’s multivariable analysis also found that jobs mostly characterized by physical activity increased the probability of reporting moderate or poor work ability while conversely, a work position characterized by the predominance of mental activity had a favorable impact on work ability. Finally, a study of 457 women and 579 men (mean age: 51 years) showed that poor and moderate baseline WAI scores were associated with lower health-related quality of life and more frequent use of primary health care 1 year later, and a WAI score of ≤ 37 was identified as the optimal cutoff to predict the need for rehabilitation (Bethge et al., 2012). Moreover, subjects with poor baseline work ability had 4.6 times higher odds of unemployment and 12.2 times higher odds of prolonged sick leave than the reference group with good or excellent baseline work ability (Bethge et al., 2012).
Advantages
The WAI is a fast and simple outcome measure to administer that has a significant amount of research in support of its use in clinical practice. Several studies involving large cohorts of subjects have also helped to establish norms for the WAI. For example, one study involved over > 12,000 subjects while several others involved more than > 1000. The WAI has also shown to have cross-cultural relevance evidenced by its numerous translations as well as an amount of international research studies pertaining to it.
Disadvantages
Work ability in general is a complex phenomenon and efforts to quantify it can be elusive. For example, a systematic review by van den Berg, Elders, de Zwart, and Burdorf (2009) determined that there were many important factors associated with a poor WAI score, which included lack of leisure time or vigorous physical activity, poor musculoskeletal capacity, older age, obesity, high mental work demands, lack of autonomy, a poor physical work environment, and high physical workloads. The authors went on to note that the impact of social and economic policies at the company and national level and their effect on WAI scores still remain largely unknown.
Administration
The WAI is a self-report measure where the subject is asked to consider a range of issues and their effect on work (10 questions). Scoring choices are composed of various numeric scales and are unique for each item. For example, dimension 2 contains 2 questions that are scored along a 5-point scale ranging from 1 (very poor) to 5 (very good) relative to subjective current work ability in relation to the physical and mental demands of work; dimension 4 uses a 6-point scale ranging from 1 (fully impaired) to 6 (no impairments), which is the subjective estimation of work impairment due to disease; and dimension 7 assesses a person’s mental resources over a 3-month timeframe using 3 questions concerning enjoyment of regular daily activities, being active and alert, and feeling full of hope about the future and uses answering categories ranging from 0 (never) to 4 (always) (Reeuwijk et al., 2015).
TABLE 104-2
THE 7 DIMENSIONS OF THE WORK ABILITY INDEX MEASURE
1. Current work ability compared with lifetime best |
2. Work ability in relation to the demands of the job |
3. Number of current diseases diagnosed by a physician |
4. Estimated work impairment due to diseases |
5. Sick leave during the past 12 months |
6. Personal prognosis of work ability 2 years from now |
7. Mental resources |
Adapted from de Zwart, B. C. H., Frings-Dresen, M. H. W., & van Duivenbooden, J. C. (2002). Test–retest reliability of the Work Ability Index questionnaire. Occupational Medicine, 52(4), 178.
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