| Burden of Disease (BOD) |
The BoD is calculated as the present value of the years in each health state times the loss of HRQoL associated with that health state. Thus, for example, if a person is expected to live for 20 years in a health state with an index of 0.8 then the person would be expected to live 16 adjusted life years which represents a BoD of 20 - 16 = 4 adjusted life years. Any reduction in the length of a person’s life due to the disease is also added to the BoD and is defined as part of the total BoD.
The WHO Global Burden of Disease[1]and the two Australian BoD studies[2]have estimated the expected years in each health state before death for every disease and multiplied these by the third index of (dis) utility described in Box 1. The adjusted years obtained this way are defined as ‘DALYs’ and the DALYs lost in each health state attributable to the disease and the expected reduction in the length of life are summed to obtain the total DALY loss from the disease.
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| Composite (holistic) utility measurement |
This term describes one of the three ways in which utility may be measured. With this approach a complete health state (consisting of multiple dimensions) is described in a vignette or brief narrative describing the health state. This is then used in a survey in which respondents are asked to evaluate and score the health state using one of the utility scaling techniques (TTO, SG, PTO). Utility may also be measured using a multi-attribute utility instrument such as the AQoL or it may be measured directly by asking patients to rate their own health state.
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| DALY (Disability adjusted life year) |
This is a concept introduced recently by the World Bank/WHO study team lead by Chris Murray and Alan Lopez. The DALY is a QALY like measure in which life years are adjusted by a utility index derived from the PTO. More specifically, PTO values were obtained for 22 health states during a series of focus groups carried out with health experts during which the health states were discussed. The 22 states were located on a rating scale and all other major diseases were then located on the rating scale in relationship to the 22 marker states, again by health experts. Results were used to estimate the burden of disease for all major disease groups in all countries.
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| Decision analysis |
This is a branch of theory that assists with decision making. In essence, complex decisions are broken down into their constituent parts (a complex health state is broken down into its multiple dimensions). The value or utility of each aspect of the decision (item or dimension of health) is independently estimated (using one of the numerous scaling techniques evolved by decision theorists). The decomposed values or utility scores are recombined using one of several possible models (additive or multiplicative being those that have been adopted by MAU instrument makers).
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| Descriptive system |
This refers to the questionnaire-like set of statements and response categories that define the health domain of a QoL instrument.
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| Dimension |
A sub-set of items which define a coherent sub-set of the quality of life. For example, physical health, mental health, social health.
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| Disease specific instruments |
Instruments structured to emphasise dimensions of particular relevance in assessing outcomes for a specific condition. Disease specific instruments are more likely to be sensitive to changes in health status for their target patient group than are generic instruments such as the EQ-5D or HUI.
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| Economic costs |
In principle, economic (or opportunity) costs represent the benefits foregone as a result of any economic activity. The economic cost of reading this glossary is the benefit that may have been obtained from reading something else or undertaking another activity. In practice, economic costs are generally measured by the market price of a commodity where this is available or by an estimated market price equivalent when it is not. Economic costs are compared with dollar benefits in cost benefit analysis and a ranking of the ratio of cost to benefits is obtained in cost effectiveness analysis and cost utility analysis.
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| EuroQoL or EQ-5D |
This MAU instrument consists of six items that define 243 response categories (Dolan, 1997). The instrument was designed for cross European comparisons of the quality of life. It was subsequently the basis for one of the largest scaling exercises to date, using the time trade-off technique. The research, carried out by Alan Williams and his colleagues at York, resulted in several sets of 'utility tariffs' each applying to a different age, sex and SES group.
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| Factor analysis |
Factor analysis collapses many items or variables into a few underlying dimensions or constructs. That is, several items assessing hearing, speech, and vision might load highly on a factor that captures the underlying HRQoL dimension of 'Physical Senses'. The association between items and factors determines the semantic content of dimensions. Factor analysis allows the structure of an instrument to be verified or empirically derived.
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| Global Burden of Disease |
refer to Global Burden of Disease.
http://www.who.int/topics/globalburdenof_disease/en/
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| Health Utility Index (HUI) |
The HUI Mark I, II and III are three MAU instruments developed by George Torrance and his colleagues at McMaster University. Along with the AQoL, the HUI instruments are the only ones to employ a multiplicative model for combining utilities.
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| Healthy year equivalent (HYE) |
This is one particular form of QALY which is derived by using the standard gamble to evaluate, not one but all of the years of life that will be experienced in a given health state. The concept has been vigorously promoted by Gafni at McMaster University. There has been a major debate to determine whether or not the HYE is conceptually different from measurement over multiple years using the TTO.
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| HRQoL (Health related quality of life) |
This is a relatively loose concept with refers to the sub-set of quality of life which may be affected by a health program. As health programs may, potentially, affect all aspects of life, HRQoL could, arguably, be considered identical with the concept of quality of life.
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| Instrument |
This term has its normal meaning viz a device for achieving a particular objective. In the present context the device is the descriptive system all questionnaire – type set of items with which a respondent can indicate – describe – their health state. The instrument may or may not have a corresponding set of utility weights. If it does not, it is commonly described as a 'psychometric instrument' (ie where unweighted response scores can be summed). Where multiple dimensions are described and utility weights or scores are included, it becomes 'a multi attribute utility' instrument.
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