Population Health Impact of Disease in Canada (PHI)

Glossary

Birth cohort
Individuals born during the same time period, for instance, those born in 1920.

Case fatality rate
Proportion of cases of a condition that are fatal; the number of deaths attributed to the condition divided by the number diagnosed.

Comorbidity
Presence of more than one disease or health condition in an individual at a given time.

Disability
Restriction or lack of ability (resulting from an impairment) to perform an activity in the manner or within the range considered normal. Although the word "disability" is widely used, the PHI avoids this term to maintain a more positive perspective on health.

Disability-adjusted life year (DALY)
Health gap measure developed for the WHO Global Burden of Disease to estimate the burden of a disease on a defined population. DALYs are measured in terms of mortality and morbidity. Morbidity is weighted to reflect the severity of the condition. DALYs are the sum of years of life lost (YLL) to the disease and years of life lived with disability (YLD).

Disability-free life expectancy (DFLE)
Health expectancy measure indicating the average number of years an individual is expected to live free of disability if current patterns of mortality and morbidity continue to apply.

Discounting
Process applied to costs, benefits, and outcomes based on the concept that money and health have greater value in the present than at some future time due to uncertainty about the future.

Disease burden
Size of a health problem in an area, measured by cost, mortality, morbidity, or other indicators. Knowledge of the burden of disease can help determine where investment in health should be targeted. The PHI uses the term "impact" of disease (and injury) rather than disease burden to measure the consequences of disease in terms of mortality and morvidity.

Full health
Best possible level of functional status an individual can imagine, free from any type of illness or disease.

Gap measure
See mortality gap and health gap measure.

Health-adjusted life expectancy (HALE)
Year-equivalents of full health that an individual can expect to live if exposed at each age to current mortality and morbidity patterns. Years of less than full health are weighted according to severity of health conditions. The HALE calculation modifies a standard life expectancy calculation by weighting the number of life years lived by each age group using the mean health state score for that age group. [more]

Health-adjusted life years (HALYs)
Number of year-equivalents of life lost by Canadians to disease or injury. Specifically it is the sum of years of life lost (YLL) through premature mortality and year-equivalents lost to reduced functioning (YERFs). [more]

Health expectancy measure
General term for indicators that combine mortality and morbidity. They indicate the average number of years an individual is expected to live in various health states if current patterns of mortality and morbidity continue to apply. Two common health expectancy measures are disability-free life expectancy (DFLE) and health-adjusted life expectancy (HALE).

Health gap measure
General term for health indicators that quantify the difference between the actual health of the population and some stated norm or goal. Two such measures are health-adjusted life years (HALYs) used in the PHI and disability-adjusted life years DALYs used in many burden of disease studies.

Health state
Distinct grouping of conditions that share a common profile of functional limitations. This could be a specific type of treatment such as palliative radiotherapy, or the effects at diagnosis for cancers having similar effects in terms of functional limitations.

Health state classification
Series of generic descriptors such as “mild pain or discomfort” (or cardinal numbers that represent them) that indicate level of severity on several attributes and distinguish the health state from others with a different profile. Profile is used as a general term for classification.

Health state description
Information about symptoms or other effects used to classify functional limitations on the various attributes.

Health state preference
See Preference score

Incidence-based measures
Indicators that estimate the future impact of new cases of a disease for a given reference period rather than the impact of prevalent cases (those living with the condition during the time period).

Life expectancy
Average number of years an individual could be expected to live based on current patterns of mortality. This indicator reflects environmental conditions in a country, the health of its people, the quality of care they receive when they are sick, and their living conditions.

Mortality gap measure
Component of health gap measures such as the HALY or DALY that estimates the impact of mortality at each age in terms of years of life lost (YLL) due to early death.

Person trade-off (PTO)
Method to elicit preferences in which respondents are asked to choose between hypothetical interventions that offer health benefits to groups of individuals in different health states. PTO has been used in some burden of disease studies, but is not used in the PHI. [more]

Population attributable fraction (PAF)
Estimate of the proportion of disease in the general population that is attributable to a particular risk factor.

Population Health Impact of Disease in Canada (PHI)
Formerly the Canadian Burden of Disease, Injury, and Risk Factors in Canada; a research program that measures the relative impact of about 200 diseases, injuries, and risk factors relevant to Canadians. [more]

Preference score
Measure of relative preference for a health state on an interval scale. In the PHI, health state lies between 0 (dead) and 1 (full health). Canadian preference scores are used to weight the years of life lived with reduced functioning in the morbidity component (YERFs) of the HALY; the weight is the difference between 1 and the preference score. This resulting weight, which measures disutility, or loss of capacity, is used in the same manner as disability weights are used in burden of diseases studies.

Standard gamble
Method to elicit preferences which measures the risk a person is willing to take in a trade-off between potentially enhanced quality of life (i.e., being cured) and a defined possibility that the treatment will be fatal. The standard gamble is the main tool used for health state preference measurement in the PHI. [more]

Summary measures of population health
Indicators that summarize the health of a population into a single number. They combine information about mortality and morbidity in a single measure. Two types of summary measures are health expectancy and health gap measures.

Time trade-off (TTO)
Method to elicit preferences in which respondents are asked to make hypothetical choices about improvements in health and longevity. Preferences for normal life expectancy in a defined health state are weighed against reduced life expectancy in good health. Reduced life expectancy is varied until the point of uncertainty. Although TTO has been used in some burden of disease studies to establish disability weights, the PHI uses the standard gamble because it proved more effective in group settings. [more]

Utility theory
How people make decisions under conditions of uncertainty. Utility is the preference that people have for health outcomes along a continuum. The PHI uses the standard gamble technique, based on utility theory, to establish preferences for various states of health on a continuum between health states "dead" (0) and "full health" (1).

Visual analogue scale
Method to elicit preferences in which respondents are asked to assess health levels associated with different health states. Individuals place these on a scale representing a continuum from "most desirable" to "least desirable." In the PHI, VAS is used as a training tool for health state preference measurement. [more]

Years lived with disability (YLD)
Component of the DALY that measures the years of healthy life lost through living in states of less than full health.

Years of life lost (YLL)
Measure of the years lost through premature mortality.

Year-equivalents of reduced functioning (YERF)
Measure of time lost to reduced functioning as a result of disease or injury, weighted for severity; the component of the HALY that measures morbidity. Preference scores are used to weight the average duration of each health state to obtain average number of year-equivalents lost due to that health state. This is multiplied by the incidence (new cases) for the health state. [more]

References
This glossary is intended as a guide for readers new to this area of research. Please consult original sources for more technical definitions.

Berthelot J-M. Health-adjusted life expectancy. In: Robine J-M, Jagger C, Mathers D et al., editors. Determining health expectancies. Chichester (UK): Wiley; 2003. p. 235-46.

International Epidemiological Association. Dictionary of Epidemiology, fourth edition. Last JM, editor. New York: Oxford; 2001.

Marthe R, Gold MR, Stevenson D, Fryback DG. HALYs and QALYs and DALYs, oh my: similarities and differences in summary measures of population health. Ann Rev Public Health 2002;23:115-34.

Mathers CD, Robine J-M, Wilkins R. Health expectancy indicators: recommendations for terminology. In: Mathers C, McCallum J, Robine J-M, editors. Advances in health expectancies. Canberra: Australian Institute of Health and Welfare; 1994. p. 34-41.

Mathers CD. Health expectancies: an overview and critical appraisal. In: Murray CJL, Salomon JA, Mathers CD and Lopez AD. Summary measures of population health concepts, ethics, measurement and applications. Geneva: WHO; 2002. p. 177-204.

Murray CJL, Salomon JA, Mathers CD and Lopez AD, editors. Glossary. In: Summary Measures of Population Health Concepts, Ethics, Measurement and Applications. Geneva: WHO; 2002. p. 757-63.