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1

epidemiology

the study of health in populations specific to diseases and conditions and how they're acquired

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goals of epidemiology:

1. describe distribution of a disease
2. identify risk factors for the disease
3. prevent the disease

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epidemic

larger than normal outbreak of a disease within a certain region

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pandemic

if a disease outbreak spreads to other parts of the world

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who is the father of epidemiology?

John Snow, english physician: the first to determine that cholera epidemic in London was a result of the lambeth company water supply contamination from the Thames river

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John Snow's legacy

paved the way for:
- cleaning the water supply in London
- Germ theory
- population and preventative medicine

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what is the leading cause of death in first world countries?

chronic disease where it used to be infection, acute disease, etc.

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behavioural epidemiology

the observation and study of behaviours that lead to health related states
- also the distribution of these behaviours

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comorbidity

having more than one disease at a time

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3 goals of physical activity epidemiology:

1. examine the relationship b/w morbidity and mortality
2. identify patterns and determinants of PA
3. use evidence to determine things for disease prevention

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morbidity

having a diseased state

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mortality

dying

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PA can be considered a burden in canada for a few reasons. what are some direct and indirect costs?

direct: drugs, hospitals, physician care
indirect: work loss due to disability, things don't get done when people are sick

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physical benefits of PA on morbidity

- decreased risk of CVD, colon cancer and type 2 diabetes
- protects against breast and prostate cancer, osteoporosis
- prevents and reduces obesity

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the most healthcare dollars are spent on these diseases

coronary artery disease
stroke
colon cancer
breast cancer
type 2 diabetes
hypertension

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psychological benefits of PA

relieved symptoms of depression, anxiety
improves mood, body image and quality of life

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history of PA and health

see slide pack for this one bc wow this is a lot

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what are the landmark studies in epi?

they provide evidence that PA and health outcomes are related
- London bus study
- Framingham heart study
- Longshoremen study
- Harvard alumni study

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London bus study

1950s UK by Jerry Morris
- a retrospective study
examined link b/w occupations PA and health by measuring heart disease in double decker bus drivers vs conductors

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what is myocardial infarction?

heart attack

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results of london bus study

found that conductors were at lower risk of heart disease than drivers regardless of their age

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what were some limitations of the london bus study?

we can't conclude anything based on this evidence.
- we don't know about their leisure activities, daily activities (eating, smoking)
- job stress?
- self selection for the job, could this be just coincidence that lazy people get CVD and choose to be bus drivers than conductors

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Framingham heart study

1949 to present in the US in small town Massachusetts
- a prospective study that followed people over time to see what happens
is there a link b/w lifestyle and health,
>5000 people : men and women, predominantly white, testing and surveyed every 2 years

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whats the difference between a retrospective study and a prospective study?

retrospective: take what you know now and look into history to find out more
prospective: follows people over time and see what happens

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results of framingham heart study

there were controllable and uncontrollable risk factors
- most things were controllable: smoking, diet, PA rates, alcohol and obesity levels
- uncontrollable: gender, genetics, ethnicity

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limitations of framingham heart study

only white people, not a very ethnically diverse pop
- this has changed now to incorporate a more diverse pop of people but initially not

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Longshoremen study

3500 longshoremen studied in 1951-1972
prospective cohort study
- dockworkers vs supervisors; looked at PA throughout the day

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results from the longshoremen study

8500kcal/week reduced risk of death due to CHD (coronary heart disease) by 50% WOW

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limitations of longshoremen study

all men
we don't know about leisure time activities
had some screenings tests but people weren't self selecting which jobs they had

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Harvard alumni study

1960s
retrospective but also kept track over time prospectively
- researchers sent questionnaires to alum. about PA habits

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results from harvard alumni study

3 hrs/week of PA could reduce overall death rates by 50%
- even walking helped decrease rate by 33%
- active men lived 2 years longer than inactive men

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limitations of harvard alumni study

white men all of high socioeconomic status (they were in uni)

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PA guidelines
** these are important **

WHO in 2011
" 150 min mod-intensity PA/week or 75 min vigorous PA/week " - in bouts of 10 mins or more
increase moderate PA to 300 min/week over time or 150 vigorous PA/week but w/e
-- resistance exercise 2 or more days/week

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risk factor

not necessarily cause of disease but increases the probability of getting that disease, compared to groups that don't have that characteristic

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incidence

new cases of a health related state that occurs in a population during a specific time period

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prevalence

number of existing cases (new and old) in a population at a specific point in time

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how to calculate prevalence rate:

# of cases in pop/
# of people in the pop

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why is it not particularly useful to know the number of incidence or prevalence rates

- it doesn't give any info about total pop or if this is a good or bad thing
THUS, it's more important to know the rates of incidence or prevalence

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how should we express prevalence rates?

as a percent or per 100, 1000, 10,000, etc

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what does it mean when prevalence rates are high?

bad: lots of people have the disease
good: people aren't dying from the disease

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how to calculate incidence rates:

# of new cases/
# of people in the pop

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categories of rates

crude, specific, and standardized (adjusted)

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crude rates

- based on total pop w/o considering pop characteristics

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specific rates

- computed separately for different sub-populations
ex. diseases that only affect women/men

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standardized rates

are adjusted so that they make sense by factoring in the effects of some known population characteristics
-- used for comparing 2 or more populations

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what is the scientific method?

a systematic way of collecting data so we can have fact based explanations about things
- results need to be reproducible

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what is research design?

an analytic approach used to evaluate a research question
- how you set up a study to examine the assoc b/w 2 or more variables

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what are the 4 steps in the scientific method?

1. developing and defining the problem
2. formulating the hypothesis
3. gathering data
4. analyzing and interpreting the results

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dependent vs independent variables

dependent: is observed and measured, does not receive manipulation
independent: is manipulated by the researcher and looked at change it causes to the DV

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hypothesis

a prediction that involves facts and guides observations
- the prediction must be testable

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how does the process of publishing scientific research work?

- submit research to a journal, the more reputable the better
- article is peer reviewed and avoids conflicts of interest
- study is accepted or rejected
-- once published, it can't be removed, it can only be retracted

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primary vs. secondary source articles

primary: actual research study that's been run
secondary: summarize a lot of research out there based on keyword searches and put it all together

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what is the goal of research design in PA epidemiology?

to answer the research question and:
- determine the effect PA has on a particular disease or condition
- determine the consequences PA has on env't, personality char, etc

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what are the 2 general types of study designs?

observational designs and experimental designs

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observational study designs

and ex.

examine the association b/w IV and DV as they occur naturally
ex. cross sectional study, prospective cohort study, case-control study

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experimental study designs

and ex.

the investigator manipulates the IV and looks at the effects on the DV
ex. randomized control trials

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cross-sectional studies

looks at one pop at a particular point in time
advantages: fast and easy to conduct

** disadvantages: can't determine direction of assoc (what caused what)
- also can't determine cause and effect

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case-control studies

pops of people w similar char. are compared to to people in a diseased pop and looks at events that may have put them at risk for the disease
adv: cheap and easy, good for studies of rare things

disadv: can't determine cause and effect
can't determine incidence rates bc not following over time
recall bias - sub can't remember correctly 10 ya

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prospective cohort studies

follows a group of people over time and sees what diseases they dev'p
adv: can study many outcomes simultaneously AND can measure incidence

disadv: can't determine cause and effect
v. resource intensive, also problem w loss of follow up

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randomized control trials

randomly assign people to experimental and control groups, change IV in exp group and don't in control
adv: GOLD STANDARD bc can determine cause and effect

disadv: v. expensive, ethical concerns (don't ask tough questions), loss of follow up, hard to examine rare outcomes

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relative risk (RR)

aka risk ratio
- risk of disease in people exposed to a risk factor relative to the people not exposed to the risk factor

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what are threats to determining cause and effect in epi studies?

confounding variables and effect modifiers

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how do we determine causes in epi studies?

5 criteria (Mills Cannons): determines if data has statistical significance
- temporal sequence
- strength of association
- consistency
- dose-response relationship
- biological/conceptual plausibility

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what is a confounding variable?

no relationship b/w A and B, it's actually a separate variable that has an effect

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effect modifiers

alters the relationship b/w A and B but a relationship still exists

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physical activity definition

any body movement produced by skeletal muscle that results in energy expenditure
ex. beings asleep then getting up

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exercise def

any form of PA w an objective such as improving health, fitness, etc

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what is physical fitness?

physical attributes relating to one's morphological, muscular, motor, cardioresp and metabolic capabilities
ex. fit but fat

it is the number one predictor of risk!

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sedentary behaviour

any waking activity (not asleep) char by energy expenditure of or less than 1.5 METS (metabolic equivalents)

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risk difference

aka attributable risk
- what's actually attributed to the risk itself
== risk of diseased among exposed - risk of disease among non exposed
- shows how much of the risk is attributable to the disease

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how many METs of energy are we using at rest?

about 1 MET

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what are some challenges of measuring PA?

- its a complex construct with many varying aspects
ie. FITT - Frequency, Intensity, Type, Time can all change
- there are diff ways people do PA (occupational, leisure, activities of daily living)

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3 things a study must be:

valid
reliable
feasible

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reliability

a study is reliable if it produces the same results over and over again

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validity

a study is valid if it actually measures what you think you're measuring
- the most valid measures are often v. expensive, making them less feasible

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feasibility

is the measurement tool you've chosen realistic to use with the resources you've got available

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3 types of measures

subjective/self report
objective
criterion
- validity increases as you go down the list
- feasibility decreases as you go down the list

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subjective measures of PA

get info through interview questionnaires or activity diaries

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advantages and disadvantages of subjective measures of PA

adv: can be done on large scale, recording a variety of measures, cheap, easy to administer and add up data

disadv: social desirability, recency effects have an influence on whether person is honest
- sometimes confusion w questionnaires

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objective measures of PA

you measures someone's PA w some type of tool collecting data
includes heart rate monitors, pedometers, accelerometers

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advantages and disadvantages of heart monitors

is an objective measure of PA, as you increase your HR you typically use more energy

adv: valid, easy to collect data and see change over time, small, noninvasive and fairly cheap

disadv: can't use on large scale studies, only measures HR, not intensity of PA

82

criterion measures of PA

reference methods/gold standards
- measure things like kcals used and energy expenditure throughout the day
include: direct observation, doubly labeled water, indirect calorimetry

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advantages and disadvantages of pedometers

an objective measure of PA, where # of steps = distance travelled = general amount of energy used

adv: get immediate feedback, CHEAP

disadv: can't tell the difference b/w types, intensity, duration of PA, if worn on hip it only monitors activities when moving up and down

84

advantages and disadvantages of accelerometers

an objective measure of PA, that measures acceleration in different planes

adv: small, moderate price range, not intrusive, memory GPS avail

disadv: error is wearing on your wrist bc not accurate for activities when you move your arms a lot
- not as good if not research grade

85

advantages and disadvantages of behavioural observation

criterion measure of PA, where 2 trained observers watch and record daily activities

adv: non-invasive, valid, accurate

disadv: expensive to pay people to observe, people may be more motivated to do more activity, not an option for large pop. studies and better for short durations

86

advantages and disadvantages of double labeled water

criterion measure of PA, considered to be the gold standard for measuring energy expenditure (4-7% error)
- ingesting H and O isotope drink and measure CO2 production from urine output

adv: stays accurate for 3 weeks
disadv: VERY expensive (drink, urinalysis) all you know is total energy expenditure for the day

ideal for small experimental studies and establishing validity of other measures such as part of a pop survey

87

advantages and disadvantages of indirect calorimetry

adv: very accurate, gives info re: intensity and duration of PA in a lab setting

disadv: costly and invasive where you have to wear a mask

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direct vs indirect calorimetry

both criterion measures of PA
direct: uses bomb calorimeter where energy expenditure=heat production from a sealed chamber
- very expensive

indirect: analysis of O2 consumption and CO2 production in expired air
- like a VO2max test

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factors affecting physical fitness

genetics: some people have to do v little PA to improve their PF, some people who do PA get worse PF

type and amount of PA- those more active generally have better physical fitness, certain types of PA are good for different aspects of physical fitness

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reasons epidemiologist measure physical fitness:

to determine if PF is:
1. an outcome of PA
2. a mediator of PA
3. a moderator of PA

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explain fitness as an outcome of physical activity

questions how PA has an impact on fitness variables directly

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explain fitness as a mediator of PA

as a middle step, PA changes the fitness variable and the fitness variable the determinant of risk
ex. PA -> PF factors -> risks of certain disease

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explain fitness as a modifier of PA

aka as an effect modifier

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how is PA prevalence studied in the world?

most developed nations use surveillance but its hard to compare a lot of the data
- so the WHO has created a standardized survey used in 40 countries

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how is PA prevalence studied in the US?

BRFSS - behavioural risk factor surveillance system
a randomized telephone survey about inactivity levels, diet, smoking, alcohol, etc

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how is Canadian PA data collected?

the canadian physical activity monitor takes national telephone surveys
respondents are 51% and most are females w a uni degree

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canada health measures survey

an accelerometer study found that surveys weren't actually true about 50% of canadians being accurate, it was more like 15%

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Factors related to PA levels

1. age: older get less exercise
2. gender: men exercise more
3. ethnicity
4. income
5. education level

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what does ethnicity have to do w PA levels?

- lowest PA rates in Asian Canadians
- highest PA rates in Aboriginal Canadians

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what does income have to do w PA levels?

it affects your ability to participate in organized PA
use sports as socialization