For a full explanation of the theory see our paper in Social Science Medicine (Zhang et al).
According to economic theory, the concept of productivity is based on the production function, where output is a function of capital input, labour input and technology which allows for substitution between different types of inputs. Productivity is a measure of output per unit of input. Labour input reflects the quantity (e.g., time) and quality (e.g., effort and skills) of the work force. Productivity loss due to health problems refers to the output loss corresponding to the labour input loss due to health problems. Productivity changes (gains), in the context of programme evaluations, represent the changes (reduction) in productivity losses due to health problems which are made by the health programme being evaluated.
Many productivity questionnaires focus on the measurement of changes in productivity inputs due to health. The VOLP aims to measure the changes in productivity output due to health.
Pauly and colleagues suggest that there are three characteristics of jobs should also be taken into account in order to assess the impact on output:
- Team production.
- Availability of perfect substitutes.
- Time-sensitivity of output.
Absenteeism and presenteeism costs can exceed the wage of the individual if their jobs involves:
- Team production, no perfect substitutes, and no time sensitivity.
- Individual production, no perfect substitutes, and time sensitivity.
- Team production, no perfect substitutes, and time sensitivity.
Subsequently, the value of an individuals productivity loss on output might be more than just the individuals wage. Studies by Pauly and colleagues have used estimates from employers to value the loss of output of individuals. However, in the context of clinical studies, asking employers of participants is unethical and impractical.
The VOLP has therefore been designed to enable the assessment of the impact of health conditions on productivity output by asking the individuals themselves.