Epi Mid Term 1

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Epidemiology:

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Human health in populations, what determines health of those individuals or diseases states that might come up. We uses this info to prevent the diseases

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What Are the 3 goals of epi

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1. describe distribution of the disease

2. identify the risk factor

3. Prevent the disease

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John Snow

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Father or modren epi

-Lodon cholera in 1854

Legacy

1. clean water supply

2. recognize germ theory

3. population and preventive medicine

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Broad Street Pump Outbreak

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1854

largest outbreak of chlorea in UK

127 people died in 3 days

All got water from the water pump on broad street

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epidemic and pandemic

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epi: rapid spread of infectious disease to a large # of people

pan: same but more global

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behavioural epi

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

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Three Goals of PA Epidemiology

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1. Examine relationship between PA and morbidity and mortality
2. Identify patterns and determinants of PA: who is active/inactive, are activity levels changing, what factors (personal, environmental) are related to physical activity
3. Use evidence to determine: how PA can be changed, extent which PA is a risk factor and impact of changes in PA

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The Burden of PA in Canada

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* direct costs: drugs, hospital and physician care etc
* indirect costs: work loss due to disability
* costs ~ 6.7 billion dollars in Canada

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Exercise and Morbidity

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* **Physical consequences

* decreases risk of CVD, colon cancer, Type 2 diabetes
* can protect against breast ad prostate cancer, osteoporosis
* prevents and reduces obesity
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* ** Psychological consequences
* relieves symptoms of depression, anxiety
* improves mood, body image, quality of life

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ORGINS OF LINK BETWEEN HEALTH AND PA

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* Exercise as Medicine
* Ancient Indian: 9th Century B.C : Exercise and massage to help rheumatism
* Greek Physician Herodicus: 480 B.C: Therapeutic gymnastics, influenced Hippocrates (father of Medicine), Aristotle (wrote a book)
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* Exercise and Health Education
* Italy: 4th Century: scholars recommend that exercise is a fundamental part of education, physician wrote a book
* North America: 1700’s on: few physicians supported PA for good health until after US civil war; links between PA and chronic diseases found in the 1800’s ; by late 1800’s PA promoted as preventative medicine ; 1954 ACSM founded

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Landmark Studies

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1. London Bus Study
2. Framingham Heart Study
3. Longshoremen Study
4. College Health Study

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London Bus Study

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(1950’s)

Purpose: Examine link between occupational PA and health

Method: Measure heart disease in double-decker bus drivers vs. conductors

* occupation PA: physical activity completed at your job
* Retrospective study: collecting data that exists already and comparing the info

Results: Conductors at lower risk than drivers

Limitations:

- one gender - could have been other risk factors

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Framingham Heart Study

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(1949-)

Purpose: Examine link between lifestyle & health prospectively

Methods: Over 5,000 people enrolled (in 1971),with tests & surveys every 2 years

* Uncontrollable risk factors (family history, age, gender)
* Controllable risk factors (smoking, inactivity etc)

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Longshoremen Study

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3500 Longshoremen studied, 1951-1972

• Cargo handlers & dockworkers vs supervisors

* look for risks of CHD
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* Limitations
* many people changed job titles

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Harvard Alumni Health Studies

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* active men vs. inactive: lived 2 years longer
* college graduates from 1919-1950
* most high status and most men because of time period
* sent them a survey ~ 21000 people returned them

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• World Health Organization (2011)

PA requirements

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* “Adults aged 18–64 should do at least 150 minutes of moderate-intensity aerobic physical activity throughout the week or do at least 75 minutes of vigorous-intensity aerobic physical activity throughout the week”
* Minimum bouts of 10 min
* moderate-intensity aerobic PA to 300 minutes per week, or 150 minutes of vigorous-intensity per week over time
* Resistance exercise 2 or more days/wk

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American College of Sports Medicine (2011)

PA requirements

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* moderate-intensity cardiorespiratory exercise training for ≥30 min/d on ≥5 d/wk for a total of ≥150 min/wk, vigorous-intensity cardiorespiratory exercise training for ≥20 min/d on ≥3 d/wk (≥75 min/wk), or a combination of moderate- and vigorous-intensity exercise to achieve a total energy expenditure of ≥500-1000 MET·min/wk
* Resistance exercise 2-3 days/wk
* Flexibility exercises 2 days/wk
* certain diseases respond to to certain exercises

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Risk factor:

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characteristic that increases the probability of disease

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Incidence:

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New cases of health-related states that occur in a population during a specific time period

- Calculation: # of new cases occurring in a population in a specified time period/ # of people in the population… expressed as a percentage or rate

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Prevalence:

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

- Calculation for Prevalence Rates: # of cases present in population / # of people in population … expressed as a percentage per 100, 1000 etc

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* Crude Rates

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* Rates are based on total population without considering population characteristics

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Specific rates

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Rates are computed separately for different sub- populations

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Standardized (adjusted)

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Rates are adjusted by factoring in the effects of some known population characteristics ; Used for comparing two or more populations E.g., over time, between regions

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The Scientific Model

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is our way of ensuring that predictions and interpretations are based on facts and the results are reproducible

1. Developing and Defining the Problem:

2. Formulating the Hypothesis

3. Gathering the data

4. Analyzing and Interpreting the results

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Research Writing Steps

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I. ABSTRACT

II. INTRODUCTION

III. THE METHODS SECTION

IV. THE RESULTS SECTION

V. THE DISCUSSION SECTION

VI. THE REFERENCE SECTION

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ABSTRACT

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Written last (it is essentially a summary)

• Re-establishes the topic of the research.

• Gives the research problem and/or main objective of the research (this usually comes first).

• Indicates the methodology used. • Presents the main findings.

* Presents the primary conclusions

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II. INTRODUCTION

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* explains why the research is being done

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III. METHODS SECTION

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Answers these two main questions:

1. How was the data collected or generated?
2. How was it analyzed?

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IV. THE RESULTS SECTION

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There are two basic ways of organizing the results:

1. Presenting all the results, then giving a discussion (perhaps in a different section)

2. Presenting part of the results then giving a discussion, presenting another part then giving a discussion, etc.\

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V. THE DISCUSSION SECTION

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1. Explanation of results

- whether or not the results were expected,

- explanations for the results, particularly for those that are unexpected or unsatisfactory.

2. References to previous research

- comparison of the results with those

reported in the literature

- use of the literature to support a claim, hypothesis or deduction.

3. Deduction

* a claim for how the results can be applied more generally (a conclusion based on reasoning from the results)

4. Hypothesis

- A more general claim or possible conclusion arising from the results (which will be supported or disproved in later research).

**CONCLUSIONS (Very important):

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VI. THE REFERENCE SECTION

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1) An in-text reference to show that a piece of information, idea, quotation, etc. you have included belongs to another writer. Always designed to be short because it is interrupting the text, and is usually in parentheses

2) Final reference provides full bibliographic information (about when and where the source was published, and by which publisher) Usually at the end of the paper.WHAT

* YOU MUST REFERENCE: All work done by other researchers that you want to refer to in your own writing.

* WHAT YOU DO NOT NEED TO REFERENCE: General knowledge

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The goal of research design in PA epidemiology

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• To clearly answer the research question and establish PA as:

* A determinant of a particular disease, health status, injury, health state, etc.
* A consequence of the environment, genetics, personality characteristics, etc. etc.

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Observational Designs:

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Examines the association between the independent and dependent variables as they naturally occur

cross sectional

prospective cohort

case control

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* Cross-Sectional Study:

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* when you take your variables at one point in time and compare them. Don’t know which is dependent or independent, look for links
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* typically starting point because your looking for possible associations
* Don’t know how the variables effect each other ( can’t see what caused what)

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* Prospective Cohort Study:

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* take healthy populations, take measures and follow them over time

AdvantagesCan study multiple outcomes simultaneously Can measure incidence

DisadvantagesCannot determine cause & effect Resource intensive“Loss to follow-up” is a problem

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* Case-Control Study:

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* take people that have the disease and compare them to people that don’t. Have to ask them questions about their history

• Advantages Inexpensive and easy to conduct Good for studies of “rare events” Hint at possible associations for further inquiry

• Disadvantages Cannot determine cause and effect Cannot determine incidence rates Recall bias: problem with people asking people to recall things from their past. Underestimation and overestimation

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Experimental Designs:

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The investigator manipulates the independent variable and looks at the effects on the dependent variable

* Randomized controlled trials:

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* Randomized controlled trials

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* placebo vs actual experiment

• Advantages The “gold standard” of research designs Can establish cause and effect

• Disadvantages Very expensive Ethical concerns Loss to follow-up Hard to examine rare outcomes

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Relative Risk (RR):

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Also known as the “risk ratio”; Risk of disease in people exposed to the risk factor relative to the risk of disease in people not exposed to the risk factor

* Steps for Calculating RR

1. Calculate the incidence of disease in people with and without the risk factor

2. Calculate the relative risk (or “risk ratio”)

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Determining Cause in Epi Studies

• Five Criteria : (Mills Cannons): need to pass all these.

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1. Temporal sequence: Come in the right order time wise

2. Strength of association: how closely linked are the factors use correlation relationship

3.Consistency: does it show a similar trend in every population youre studying

4. Dose – response relationship: if you have more risk factor the more of the diease you’ll get

5. Biological (or conceptual) plausibility: need to explain relationship using physiologyly or biologically

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Threats to determining “cause and effect”

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Confounding

* A “third” variable that could account for the relationship between “A” and “B”
* The magnitude of the relationship between “A” and “B” depends on a “third” variable
* E.g., life stress >> illness

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Physical Activity

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Any body movement produced by skeletal muscle that results in energy expenditure

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• Exercise:

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Any form of physical activity undertaken with a specific objective such as the improvement of fitness, health, or physical performance

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Physical Fitness

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Physical attributes relating to one’s morphological, muscular, motor, cardiorespiratory, and metabolic capabilities

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Considerations when Choosing a PA Measure for a Study a PA Measure for a Study

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* Is the measure valid?
* s the measure reliable?
* s the measure feasible?

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Three Types of Measures

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1. Subjective(self-report)
2. Objective
3. Criterion

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Subjective Measures of PA

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Questionnaires and Activity Diaries Logs

Advantages:

* measure in large populations because you don’t do the work
* doesn’t cost a lot of money
* measure details (what type or activity etc)
* bias not accurate

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Objective Measures of PA

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1. Heart Rate Monitors

2. Pedometers

3. Motion Sensors

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1. Heart rate monitors

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* Basis: there is a relationship between your heart rate and the amount of oxygen your body uses, therefore in turn how much energy you expend … the higher the heart rate the more activity the person is doing
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* Advantages
* Disadvantages

- cant do it on large population groups

- heart rate can be affected by other things which can be misinterpreted for pa

- missing the type of exercise they’re doing

- heart rate stays high after physical activity

- everyones heart rate is different

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2. Pedometers

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* Basis: measuring number steps you take to show how far a person’s travelled
* Advantages
* Disadvantages

- only measure up and down movements (so if you’re riding a bike it will detect it)

- super sensitive, not accurate

- cheating

- only measuring number steps not measuring stride length

- can’t measure intensity

- doesn’t know the type of activity

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Motion Sensors or Accelerometers

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Basis: measures changes in movement (accelerations and deceleration) in different directions

Advantages

- pick up different type of movement

- determine intensity better

- good at determining duration

- can include heart monitors

Disadvantages

- don’t measure things like biking

- measuring accelerations.. don’t know the difference between being a car or walking

- doesn’t measure unless arm is moving

- can be expensive

* results not always reproducible or valid

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Criterion Measures of PA

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1. Behavioural Observations

2. Doubly Labeled Water

3. Calorimetry

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. Behavioural Observation

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* Trained observers watch and record activities
* Advantages
* Disadvantages

- time consuming

- can’t do it on a large population

- need 2 people for accuracy

- placebo (try to please)

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2. Doubly labeled water

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* ‘gold standard’ for measuring energy expenditure (4-7% error)
* Ingest hydrogen and oxygen isotopes
* Measure CO2 production from urine output
* Advantages
* Disadvantages

- only measures energy expenditure of only one day

- no info about the type of activity etc

- expensive

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Calorimetry

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* Direct Calorimetry
* Energy expenditure = heat production
* Measure of heat production in sealed chamber
* Indirect Calorimetry
* Analysis of oxygen consumption/CO2 production in expired air
* indicate if you’re using carbs or not for energy
* every oxygen your use = 5kcal lost
* Advantages
* not as expensive
* Disadvantages

- can be invasive

- can’t use on large populations

- you’re not collecting long periods of activity

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1. Outcome of physical activity

2. Mediator of physical activity

3. Moderator of physic

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Epidemiologists Measure Physical Fitness to Determine if it is a...

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* Morphological

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* Body mass for height
* Body composition
* Subcutaneous fat distribution Abdominal visceral fat
* Bone density
* Flexibility

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• Muscular

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* power
* endurance

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* Motor

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* Agility
* Balance
* Coordination
* Speed of movement

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* Cardiorespiratory

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* Submaximal exercise capacity
* Maximal aerobic power Heart functions
* Lung functions
* Blood pressure

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* Metabolic

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* Glucose tolerance
* Insulin sensitivity
* Lipid and lipoprotein metabolism
* Substrate oxidation characteristics

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PA prevalence

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* Need to establish activity levels and activity patterns in the population (prevalence)
* Self-report
* Representative random sample
* Data collected at regular intervals
* Track changes in prevalence over time
* “Secular trends” – natural variation
* Effects of PA-promoting interventions
* Most developed nations use surveillance
* Efforts to standardize measures

USA: BRFSS – behavioral risk factor surveillance system

• Inactivity, diet, smoking, alcohol, etc.

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Collection of Canadian Data

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• Canadian Physical Activity Monitor: 11 national surveys from 1981-2004

• Measures physical activity and correlates: Leisure time activity, physical activity, sport

* Data collection
* Random-digit dialing
* N = 6033, proportional to provincial populations
* Response rate was 51%
* Respondents more likely to be female with uni. degree

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Factors Related to Physical Activity Levels

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1. Age: PA decreases as we get older
2. Gender: men are more active than women
3. Ethnicity: (lower rates in Asian Canadians and Highest in Aboriginal)
4. Income: The more you make the more active you are
5. Educated (the more educated you are the more PA you do)