erin (L1)

Question 1

Definition of epidemiology

Answer 1

Epidemiology is the study of diseases in populations

Compares level of infection between diff groups

Question 2

steps of epidemiology

Answer 2

Diagnosis & prognosis
Identify the likely ETIOLOGY or cause of disease.
Identify the RISK FACTORS – those that increase a persons risk for a disease.
Determine the extent - quantify the incidence or prevalence of disease

Question 3

questions asked in the epidemiological approach

Answer 3

Is there an association between exposure to a variable (e.g. exposure to environmental agent or characteristic of a person such as high cholesterol levels) and development of disease in question?
Is this difference real?
Why have they occurred?
From observations to prevention/control

Question 4

what is the target population

Answer 4

target population = population at risk

• The population that have the potential to get the disease of interest - e.g. UK women are the population at risk of breast cancer in women in the UK
• If we were interested in all breast cancer in the UK we would need to include all men in the UK as well (about 300 men get breast cancer each year)
• We might limit the population to an age group at greatest risk, e.g. women over 18, or women over 50

Question 5

can you study an entire popualtion?

Answer 5

you cannot study whole populations

Can access a subset of the target population, the STUDY POPULATION ((e.g. women who have presented to their doctor in 2009))

Study population is sampled to give the STUDY SAMPLE

• Typically defined by age, sex, race, geographical location
• Should be REPRESENTATIVE of target population

Question 6

how do you measure disease?

Answer 6

AS A PROPORTION
a / (a+b)

AS A RATIO
a / b

Question 7

rate vs snapshot

Answer 7

RATE = How fast the disease is occurring
Rate = Expresses the relationship between an event and a defined population evaluated over a specified time period

SNAPSHOT - measure of the disease at a specific point in time

Question 8

define incidence and give its equation

Answer 8

The number of NEW cases of a disease in a TIME period - it is a rate

INCIDENCE = Number of new cases of a disease occurring in the population during a specified time period / Number of people who are at risk of developing disease during that period of time.

denominator is the people at risk

Question 9

define prevalence and give its equation

Answer 9

How much of a disease there is in a population at any one time - it is a snapshot

PREVALENCE = Number of cases of disease in the population at a specified time / Number of people in the population at that time.

Question 10

Types of prevalence estimate

Answer 10

Prevalence or POINT PREVALENCE: the amount of a variable at one point in time

• typical (previous slide)
• “Do you currently have asthma?”

PERIOD PREVALENCE: the amount of a variable over a defined time period

• eg. number of women with breast cancer in 2014
• eg. “Have you ever had asthma during the last 5 years?”

Question 11

Incidence vs. Prevalence

Answer 11

The prevalence of a disease is dependent on

• The incidence, i.e. how quickly new cases develop
• How long the disease lasts due to deaths or recovery
• prevalence = incidence x duration of infection (time)

Incidence is a measure of risk, prevalence is not
- incidence = prevalence / duration of infection (time)

Question 12

How do we measure what is causing disease?

Answer 12

A variable is something that we are interested in that varies!

(( Examples include: age, race, diseases, and exposure ))

Question 13

2 types of variables

Answer 13

A response or dependent variable
–> The variable that we expect to be influenced by other variables

A predictor or independent variable
–> The variables that change our response variable

[[ examples - Disease occurrence (dependent) influenced by age (independent)
Cervical cancer (dependent) affected by papilloma virus exposure (independent) ]]

Question 14

define a risk factor

Answer 14

A RISK FACTOR is a variable which is associated with an increase or decrease in a disease.

Measuring associations between risk factors and disease incidence

• Risk ratio (RR) = relative risk
• Odds ratio (OR)
• Attributable risk (AR)
• Population Attributable risk (PAR)
• Attributable Proportion

Question 15

statistical association (2x2 table)

Answer 15

Risk factor is on the y axis - anything that could drive the disease
Disease is on x axis - individuals in a band are exposed and have the disease / b band are exposed and do not have the disease

a+c = number of individuals in population with the disease
a+c/n = prevalence of disease in population
a+b = total number of people exposed to that risk factor
a+b/n = proportion of population that smokes

Question 16

risk ratio RR equation

Answer 16

Risk Ratio = risk of disease in exposed / risk of disease in unexposed
= (a/a+b) / (c/c+d)
= (a/a+b) x (c+d/c)

calculated as a ratio of proportions

Question 17

risk ratio possible outcomes

Answer 17

If RR = 1 Risk in exposed is equal to risk in non-exposed (no association)
If RR > 1 Risk in exposed is greater than risk in non-exposed (positive)
If RR < 1 Risk in exposed is less than risk in non-exposed (negative)

Question 18

odds ratio equation

Answer 18

Odds Ratio = odds of disease in exposed / odds of disease in unexposed
= (a/b) / (c/d)
= ad / bc

Question 19

odds ratio possible outcomes

Answer 19

If OR = 1 Odds in exposed is equal to odds in non-exposed (no association)
If OR > 1 Odds in exposed is greater than odds in non-exposed (positive)
If OR < 1 Odds in exposed is less than odds in non-exposed (negative)

Question 20

what do these ratios tell us? (RR and OR)

Answer 20

How strong the association between disease and exposure

• e.g. (relative risk) smokers are 1.5 times more likely to die from heart disease than non-smokers
• e.g. (Odds ratio) OR for 1 year or more of oral contraceptive use, relative to less than 1 year of use, was 1.5 (95% confidence interval: 1.2 to 1.8)

A measure of effect is useful to evaluate aetiology (causality)

Question 21

define attributable risk and its equation

Answer 21

the amount of disease attributable to an exposure in those exposed

attributable risk = risk in exposed - risk in unexposed
= (a/a+b) - (c/c+d)

Useful because allows assess important causes of death/disease in the population?

Question 22

define the Population attributable risk (PAR) and its equation

Answer 22

The amount of disease attributable to an exposure in the population

Population attributable risk = attributable risk x prevalence of exposure in population

Population attributable risk measures potential impact of control measures in a population, and is relevant to decisions in public health

Question 23

define the attributable proportion

Answer 23

Proportion of disease that would be eliminated in a population if its disease risks were reduced to that of unexposed persons

Used to compare the potential impact of different public health strategies

Gives numbers of lives saved