Hodnocení a měření zdraví Hynek Pikhart Outline • What is health and what is population health? • Rate, proportions, incidence and prevalence What is health? • Health is a multifaceted concept and not easily measurable. • WHO definition: – Health is a state of complete physical and mental well-being and not merely the absence of disease or infirmity (WHO, 1948) – stav kompletní fyzické, duševní a sociální pohody a nikoliv pouhé nepřítomnosti nemoci či vady Criticisms of the WHO definition • Is it achievable? • Can it be measured? • Change in the burden of health since 1948 • But various estimates show that among 70-95% of individuals could be classified as unhealthy on the basis of WHO definition A better definition? • Bircher (2005): “a dynamic state of well-being characterised by a physical and mental potential, which satisfies the demands of life commensurate with age, culture and personal responsibility” OR • Huber et al (2011): “the ability to adapt and self manage in the face of social, physical and emotional challenges” What is population health? • “The health outcomes of a group of individuals, including the distribution of such outcomes within the group.” Kinding and Stoddart (2003) What do we mean by outcomes? What do we mean by groups? What do we mean by distribution? Population health outcomes • Mortality – Rates of death – Life expectancy • Morbidity – Disease: biochemical (e.g. blood glucose), physiological (e.g. blood pressure), and pathological (e.g. tumour size) – Disability or impairment – Self-reported and patient-based measures • General and composite measures Tools of measurement (I) • Numbers – actual number of events – Example: 100 cases of TB in Camden Tools of measurement (II) • Proportion – a type of ratio in which the numerator is included in the denominator, often expressed as a percentage – Example: proportion of diabetics in the population • Rate – frequency with which an event occurs in a defined population, usually in a specified period of time – Example: mortality rate in 2014 Numerators and denominators • The number of cancer cases in the UK is 247,667 whereas in Belgium it is 47,948. • The UK has a bigger problem in numerical terms. • But do Belgians have lower risk of getting cancer? – Numerators alone are meaningless – We need both numerators AND denominators Numerators and denominators • The number of cancer cases in the UK is 247,667 whereas in Belgium it is 47,948. • The UK has a bigger problem in numerical terms. • But do Belgians have lower risk of getting cancer? – Numerators alone are meaningless – We need both numerators AND denominators • UK: 247 667 / 60 000 000 = 0.00413 = 413 per 100 000 • Belgium: 47 948 / 10 000 000 = 0.00479 = 479 per 100 000 Type of rates • Crude rates: apply to the total population in a given area • Specific rates: apply to specific subgroups in the population (e.g. age, sex) or specific conditions • Standardised rates: used to permit comparison of rates in the population in which differ in structure (e.g. age structure) Population at risk • People who are potentially susceptible to the event • Populations are not static as a result of births, deaths and migration “Conventional” measures • Prevalence of a disease / exposure • Incidence of a disease • Mortality – all causes vs. cause-specific rates – all ages vs. age-specific rates • Life expectancy – At birth – At specific age Prevalence • No. of existing cases / number of persons in study • Per 100 (=%), per 1000 etc Prevalence • Prevalence – Frequency of existing cases in a defined population at a given point in time. – Measure of disease burden – Can tell us point prevalence: the probability of people with a condition at a given point in time, or over a short period of time, period prevalence – All person with a condition/total population at risk – Often expressed per 1000 when frequency is small relative to population Incidence • No. of new cases / number of persons in study • Denominator: – Free of disease at the beginning of follow up – At risk: can develop the disease (e.g. non-vaccinated) • Per 100 (=%), per 1000 etc. • Incidence risk: per X persons at risk • Incidence rate: per X person-month (pyrs etc) Incidence • Incidence – Number of new events in a defined population within a specified period of time. – Direct measure of risk that healthy people will develop a condition during a specified period of time – Tells us the rate at which new conditions occur in a defined, previously condition-free group of people – Number of new cases/ total population at risk Relationship between prevalence and incidence • The prevalence of a health-related outcome depends both on the incidence rate and the time between onset and recovery or death. • Prevalence = Incidence x Average disease duration • E.g. volume of water in watertank depends on – Inflow – Outflow Life expectancy Numbers of women expected to die at each age, out of 100,000 born, assuming mortality rates stay the same as 2010-2012. The expectation is 83 (mean), median 86, the most likely value (mode) is 90. Survival and health curves Healthy life expectancy (HALE) • Healthy life expectancy (HLE), or health-adjusted life expectancy (HALE) measures the number of years that a person at a given age can expect to live in good health, accounting for mortality and disability • = the average number of years that a newborn can expect to live in "full health"—in other words, not hampered by disabling illnesses or injuries. • Summarises mortality and non-fatal outcomes in a single measure of average population health • Can compare health between countries or measure changes over time • Can inform policy questions dependent on how morbidity changes as mortality decreases Life expectancy (LE), healthy life expectancy (HLE) and proportion of life in "Good" health for males and females at birth in England, 2011 to 2013 (ONS 2015) Healthy life expectancy at birth by country, 2010 The Lancet 2012 380, 2144-2162 A – male HALE ; B – female HALE References • Bircher, Johannes. 2005. “Towards a Dynamic Definition of Health and Disease.” Medicine, Health Care and Philosophy 8(3): 335–41. http://dx.doi.org/10.1007/s11019-005-0538-y. • Huber, Machteld et al. 2011. “How Should We Define Health?” BMJ 343. • Kindig, David, and Greg Stoddart. 2003. “What Is Population Health?” American Journal of Public Health 93(3): 380–83. http://dx.doi.org/10.2105/AJPH.93.3.380. • World Health Organisation (WHO). 1948. Preamble to the Constitution of the World Health Organisation as adopted by the International Health Conference, New York, 19-22 June 1948.