Functional Health Status

The health of a population cannot be measured merely by mortality rates and causes of death – the ability to function for those who may have become sick or disabled as the result of a disease or injury, is also an important measure if we are to have a true picture of a population’s health. For example, back pain or the loss of a limb may detract from one’s overall health and therefore that detriment should be taken into account. One key measure developed —disability-adjusted life year, or DALY —is an important yardstick in health care accountability because it allows measurement of not only loss of life but of reductions in function that may result from sickness or injury. IHME’s Functional Health Status research team works to assign ‘weights’ to these health states so that estimates can be made about the overall scale of disabilities. In addition, this information helps calculate the years lived with disability (YLD), which is a critical output of the GBD Study.

For the GBD 1990 Study, disease experts were asked about how they would rank the relative weight of various health states. In this new round of the study, information is being solicited from a much wider range of sources including in-person surveys in four diverse countries, a web survey, as well as expert input. In addition, the GBD 2005 Study will use revised and refined definitions of the disabilities, which were not previously available during the GBD 1990 Study.

Another critical component to obtaining an accurate picture of disease and injury impacts is the development of standardized measurements of functional health states so that meaningful comparisons can be made over time and across populations. IHME is similarly working on the development of methods to enhance comparable measurement.

The information we are generating is essential in order for policymakers, public health officials, and others to understand the scale of disease burden in their communities. The current round of the disability weights study that IHME is conducting as part of the GBD Study will be the most comprehensive thus far and therefore is anticipated to produce the most accurate numbers to date.

Major activities in Functional Health Status:

Gather health state valuation data:

One important component of deriving final estimates of the burden of diseases is assessing disability weights to individual health states. Health states are defined as the unit to which a single disability weight is assigned, under the simplifying assumption of a constant, homogeneous state for some specified duration. The set of health states and disability weights used in the original GBD 1990 Study is now incomplete, given potential additional causes and related outcomes. Using the original list of health states as a foundation, this year IHME has solicited expert groups affiliated with the GDB Study for a more complete list of health states to consider.

Researchers are collecting data in two different ways:

  1. Community valuation of selected health states using discrete choice methods in a household survey using a subset of the overall list of states.
  2. Web survey using discrete choice methods for the entirety of the list of states.

Data collected from each exercise is being used to assess an overall ranking of health states and to attribute disability weights accordingly.

Development of methods to enhance the comparability of self-reported functional health status:

Valid, reliable and comparable measures of functional health status are critical inputs for quantifying the burden of disease especially in ageing populations. Measuring functional health status with self-reported items on surveys is a popular strategy, because it is feasible at relatively low costs and easy to administer. Self-reported functional health status has already been incorporated in a number of household health surveys over the past decades. Questioning techniques to derive responses from survey participants, however, vary across surveys, which renders comparison across populations and/or over time to be difficult.

One of the goals of this activity is, therefore, to develop methods to identify and correct systematic reporting errors arising from different question techniques, by introducing more objective external information, such as measurements from performance tests and anchoring vignettes. One example of IHME’s work in this area is the recently published study on trends in the prevalence of hearing loss in US adults by Ikeda et al (2009). This was the first study to provide comparable estimates of long-term trends in the prevalence of hearing loss among US adults from the late 1970s to the early 2000s. After establishing that biases in self-reported hearing measures vary substantially across different survey instruments and move in different directions according to the age of respondents, we used regression methods to make full use of available data and to enable adjustment and comparison of self reports by leveraging audiometric testing data from more recent years.

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