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Two-factor Work Ability Index (WAI)

What is the "Work Ability Index" (WAI)?

The Work Ability Index (WAI) is an instrument for calculating and ascertaining individuals' ability to work.

How is work ability defined in the WAI?

Work ability is defined as a person's potential to manage his/her work, taking into account the person's mental and physical resources.

In this respect, the framework for the operational assessment of work ability in the WAI is provided by the effective performance of work in both the present and future according to the physical and mental demands as well as the individual's health and personal resources. The WAI is often used in combination with other survey instruments in order to assess the different aspects determining or affecting work ability.

What does the WAI indicate and for what purpose is it used?

The WAI indicates the self-assessed work ability of individuals, considering seven indicators, which include physical and mental demands, diseases and work impairments due to these diseases, days of sick leave, as well as the individual's personal resources.

Due to the increasingly older population and, as a result, increasingly older employed persons, both employees themselves and social security systems face the challenges of maintaining work ability and counteracting inability to work by means of prevention and intervention. The WAI is a suitable and freely available instrument for determining work ability and for drawing adequate conclusions for prevention and intervention based on the results of the analyses.

Why should two factors be calculated for the WAI?

The Work Ability Index (WAI) is an established instrument for assessing work ability via self-report. It was developed as an unweighted sum score based on the assumption of one-dimensionality, which is now controversial.

Recent research supports the existence of a two-factor structure of the WAI. The first factor is called subjective work ability and resources and includes four indicators: WAI 1 Current work ability compared with the lifetime best, WAI 2 Work ability in relation to the demands of the job, WAI 6 Own prognosis of work ability 2 years from now, and WAI 7 Mental resources. The second is called health-related factor and includes three indicators: WAI 3 Number of diseases diagnosed by a physician, WAI 4 subjective estimation of work impairment due to diseases, and WAI 5 Sick leave during the past year (12 months).

In previous studies, it has furthermore been demonstrated that the seven WAI indicators have a varying degree of influence on work ability. A weighted calculation of the index values for the two factors was therefore developed. Consequently, the values are more precise and correspond to national and international studies that have identified a two-dimensionality of the WAI.

Which WAI questionnaire was used for the norm sample?

A modified short version of the classic WAI, translated into German was applied. In this version, for the indicator WAI 3 Number of diseases diagnosed by a physician, the 51 individual disease diagnoses in the long version were narrowed down to 14 higher-order disease groups. Furthermore, only diagnoses from the last 12 months were considered in the analyses of indicator WAI 3.

What values can the WAI factors achieve?

The first factor subjective work ability and resources can obtain values between 4 and 31.

The second health-related factor can obtain values between 3 and 18.

What information is available on the norm sample?

The population for the collection of data consisted of all employees subject to social security contributions registered with the Federal Employment Agency (Bundesagentur für Arbeit) as of 31 December 2010 and who were born between 1951 and 1980.

Analyses carried out by infas Institute for Applied Social Sciences show that the distributions of regional and socio-demographic characteristics in the sample of actual respondents differ only slightly from the distributions of the population as a whole. This indicates a high quality of the sample and allows for the generalisability of results of the present work to the overall population.

A detailed presentation of the socio-demographic data of the S-MGA sample is available from:
Rose et al.: The Study on mental health at work: Design and sampling. In: Scandinavian journal of public health 45 (2017), issue. 6, pp. 584-594.

For which target group is a comparison with the norm values available?

The norm sample allows for comparisons of the results regarding the two factors of the WAI for all employees subject to social security contributions who are registered with the Federal Employment Agency (full-time and part-time employees as well as mini-jobbers with a monthly income of <400 Euros) between 31 and 60 years of age.

The transferability of the WAI's structure to freelancers, self-employed persons and civil servants as well as persons aged under 31 or over 60 years of age has not yet been examined.

Any application of the procedure beyond these restrictions would therefore be based on untested assumptions about these subpopulations.

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