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Trinity College Courses
Caroline Barakat

HLTC07: Patterns of Health, Disease, and Injury Lecture 1: Introduction Introduction  Definitions  Link between epidemiology, demography & public health Definition: Epidemiology  Epidemiology – addresses human populations with respect to their health o Anything related to the frequency of ill health o Frequency quantified - Rate of its occurrence o Incidences, prevalences, case fatality rates etc., these are all epidemiological measures o They’re frequency of an event happening that’s health related (anything related to disease, death or injury) o We’re trying to quantify frequency; see what the rate of occurrence is --> how fast is it propagating in a o certain population  Prevalence – proportion of individuals afflicted by the illness at a particular time divided by the entire population that is exposed to something/susceptible to the illness  Incidence – proportion of individuals in a population that receive the illness at a particular time o If it takes the form of an event, something that occurs at some point in time – person gets sick, then gets better – it’s an event, as opposed to a health state, then it’s referred to by incidence o Example: # of contacts that were in contact with a certain communicable disease, got it at a certain point o Contact becomes an incident rate o Incidence rate: how many people get it in a certain population vs. incidence density = in terms of a population-year event  Incidence Density: the # of cases that are occurring/diagnosed in a given amount of population time ex: o –e.g. 10 000 person-years o Calculating relative to the expectancy of a human; person will live 80 yrs, go on with no cancer; incidence density = gives an idea at one point in time of a human population at a certain yr, someone gets the disease o Incidence density = how dense is it in a population? But it takes into account people's lifetimes (life expectancy) Features of 'Epidemiology'  Endemic versus epidemic versus pandemic  Endemic: when infectious/non-infectious disease is present in a population at a relatively constant (usually low) level at all times (no change in incidence over time) o Normal expectancy rates in a certain place  Epidemic: when infectious/non-infectious disease rate (# of new cases or incidence) suddenly increases above the expected or normal level for a short time in a localized area o Exceeds the norm  Pandemic: when number of disease cases occurring worldwide suddenly increases o If it exceeds the norm and becomes global health problem  Epidemiology makes distinction between what rates are used and the frequency (how broad-state is the  event?)  Knowledge base - epidemiologists use is based on research and science (compare across regions, across time; so they know if epidemic, pandemic etc.)  Main motive of epidemiologists is to find out causation (although distribution of disease is also important: how many people afflicted, where etc;)  When looking at epidemiology, have to keep in mind that not just the distribution of disease that’s important  What causes the epidemic/pandemic? What causes it to occur in a society? o Causation – etiology / etiogenesis or illness o E.g. causal (attributable) rate ratio such as the study of cigarette smoking in the etiology of lung cancer o x causes a disease y --> if we stop x, what does that do for that disease y (let’s say you reduce/mitigate x, what happens to disease y) o Ex) link between cigarette smoking and the etiology of lung cancer; looked initially at distribution; then looked at causation: if we reduce the amount of smokers in a society, what does that do to the outcome of lung cancer? --> so, you’re looking at this attributable risk --> how much does it reduce by  Research shows that incidence density of lung cancer among those that smoke is 10X higher than those that don’t smoke --> this is related to concept of attributable risk -->how much is it b/c of cigarette smoking? o Ex) eating fast food and etiology of diabetes --> by looking at calculating attributable risk, you can see how much it would benefit a certain society if we were to reduce x (# of fast food places etc;) and how that changes risk for diabetes  Aggregate of differentiated sub disciplines o Can’t call epidemiology a discipline; it is a field b/c it consists of many diff sub-disciplines and related research; although there are specific tools o Geographer o Anthropologists o Mathematicians proficient in disease modelling --> become epidemiologists --> interested in health distribution and causation Definitions: Demography  Demography – the study of populations (size and structure) o Look at the distribution of dynamics influencing their size o Dynamics: birth rate, death rate, immigration, emigration --> look at all of this with a focus of how is the population changing in terms of size and structure o Size: think of the population as a whole o Structure: younger, older, middle age altogether o Current news: aging population of Canada increasing  Need to forecast job, healthcare and education needs by looking at population structure  60 years - population more than doubled to exceed 7 billion o Human populations took hundreds of thousands of yrs to grow to 2.5 B in 1950; but then there was population explosion within 60 yrs – between 1952-2010, the global population more than doubled to 7B  Growth rates- 2% in the late 1960s o Most of the growth in developing countries o Implications on many things besides resources (global and regional implications)  This is something that people can’t dismiss o The main reason behind population surge is b/c death rate has fallen faster than the birth rate (the birth rate hasn’t necessarily gone up b/c rate of growth has decreased since the 1960s); but the death rates have fallen down faster than the birth rates --> results in rapid population growth o Lower death rates and higher birth rates have exploding population (more people being born than dying)  Currently about 1.2%/yr –70 million people each year o Although growth rates have fallen from their all-time highs; we had growth rates that were sitting globally at 2% in 1960s; current growth rate = 1.2% per year (has gone down in terms of the difference between the birth rate and death rate = growth rate) o But what does it mean in terms of population expansion  Means about 70M people each year added to Earth, that’s why the population is increasing  High projection - around 2.6 children per woman  Medium projection - 2.1 children per woman  Low projection - 1.6 children per woman Dynamics of population growth  Study by UN: o Looks at projections until year 2300 o Main reason for population expansion is fertility (=average # of children a woman has) o Projections takes into account fertility to project population sizes whether LOW, MEDIUM or HIGH  Based on local fertility averages  If you look at the high projection --> 2.6 children for women --> at a global rate, we are NOT there, we’re at fertility rate of 2.04  Medium projection: 2.1 children/women is assumed  Low projection: 1.6 children/woman assumed (lower than what we have currently)  3 diff scenarios; with what we have now, it looks like we could be going along the red path (medium projection)  Looking at population growth in a specific country; looking at the system altogether – globally – immigration, emigration doesn’t really matter, go from one place to the next, the only thing that would matter is birth rates and death rates  But if you look at it at regional level, you’re looking at whether population changes based on 2 main factors o Natural change:  # births (aka nativity rates)-# deaths (mortality rates) o Net migration change  Net immigration – net emigration  add these 2 together, you’ll know whether that population is going to increase/decrease  Need to know dynamics of population growth for several diff reasons: perhaps need to increase taxes, take pension initiatives, new schools, university, hospitals o Will show how population structure will change over time  Net migration: difference between people who come or leave a specific country  Purpose: growth, education, health care, development within the city for the growth of the population The Demographic Transition  Transformation of a population that is usually characterized by high birth rates and high death rates to one in which people tend to live longer and raise smaller families = demographic transition  The differences in death and birth rates for a model of a country that’s going thru demographic transition o Stage 1: High birth and high death rates (have a population that’s expanding)  Shown via population pyramid; blue = male; pink = female; diff age groups  X-axis = percentage of the population that is w/in each of the age groups  In stage 1, see that the majority of the population is younger (lots of people being born) but there’s also a high death rate --> so you have population pyramid upside down cone structure  Stage 1 where demographic transition didn’t occur yet; this has high birth and death rates o Stage 2: Birth rates tend to remain high but the death rates tend to go down (people being born and people are living longer, aging and moving up) o Stage 3: Death rates continue to go down (people living longer) but you also see that the birth rates are going down; birth rate going down tremendously  A lot of us are living longer and having less kids  People are being born but not as fast and they’re living longer  Parabolic o Stage 4: Countries like Canada have achieved this where the death rates and birth rates tend to be low (no birth, no death; levelling of demographic transition; not many people having children)  Bulging in the middle  If birth rates continue to fal
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