Comparison of instruments used to measure quality of life impacts of illness and injury

Due to finite resources, many public health decisions are made after weighing the costs versus the benefits (comparing programs, drugs, procedures, etc).  Decision-makers often use cost-effectiveness, cost-benefit, and cost-utility analyses in these decisions.  While costs reflect the costs of the program, the other half of the ratio reflects the impact on health.  Measures of quality of life (e.g. Disability-Adjusted Life Years (DALYs), Quality-Adjusted Life Years (QALYs)) are used to account for the impact of a health state on both quality and quantity of life.  Globally, many different instruments are used to measure quality of life.  The estimates are based on the impact of the health state on varying dimensions of health (e.g. mobility, cognitive ability) and the degree to which these dimensions are valued by society. However, comparisons of instruments have found varying estimates of quality of life impact for the same illness or injury.  This study explores reasons for this variability.  Using a systematic literature review we identified instruments used in the public health field to assess quality of life.  We examined the instruments’ characteristics, strengths, and weaknesses.  From the larger literature review we extracted studies that validated and/or used these instruments.  We compared the instruments by the different health dimensions that the quality of life measure is based on and further compared the levels within each dimension.  We found that variations in estimates between instruments can be attributed to varying degrees to several factors: 1) Differences in dimensions covered by the different instruments and/or the selection of levels within each dimension;  2) Differences in the underlying valuation task that determines preference weights; and 3) Validation studies vary in quality and are based on different populations.