Lecture 1. Measuring Disease

Question 1

What is the definition of epidemiology?

Answer 1

Epidemiology is the study of diseases in populations (emphasis on populations)

Question 2

What does prognosis mean?

Answer 2

Outcome

Question 3

What is a key indicator to see if someone is HIV positive or negative?

Answer 3

The CD4 lymphocyte count

Question 4

What can we ask from an epidemiological study?

Answer 4

Diagnosis, prognosis
Determine the extent – quantify the incidence or prevalence of disease
The why behind the disease - identify the likely etiology and risk factors

Question 5

What does etiology mean?

Answer 5

The cause of disease

Question 6

What are risk factors?

Answer 6

Those that increase a persons risk to a disease

Question 7

What questions are asked by taking an epidemiological approach?

Answer 7

Is there an association between exposure to a variable and development of disease in question?
Is this difference real? Why have they occurred?

Question 8

What two ways can a disease be measured?

Answer 8

Ratio and Proportion

Question 9

What is a ratio?

Answer 9

a/b
Relationship between two quantities, e.g. dilute this reagent 1:4 means for every 1 part reagent add 4 parts buffer

Question 10

What is a proportion?

Answer 10

a/(a+b)
Specific type of ratio comparing to a whole

Question 11

What is rate?

Answer 11

How fast the disease is occurring

Question 12

What is a snapshot?

Answer 12

Expresses the relationship between an event and a defined population evaluated over a specified time period

Question 13

What is incidence?

Answer 13

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

Question 14

What two factors make up an incidence recording?

Answer 14

A rate and a proportion (e.g the proportion of women diagnosed with breast cancer this year)

Question 15

What does the denominator of incidence represent?

Answer 15

The people at risk

Question 16

What is prevalence?

Answer 16

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

Question 17

What two factors make up a prevalence recording?

Answer 17

A snapshot and a proportion (e.g the proportion of women with breast cancer today)

Question 18

Does incidence have units?

Answer 18

Yes, e.g people per year

Question 19

Does prevalence have units?

Answer 19

No

Question 20

What is point prevalence?

Answer 20

The amount of a variable at one point in time
Typical (e.g do you current have asthma?)

Question 21

What is period prevalence?

Answer 21

The amount of a variable over a defined time period
e.g the number of women with breast cancer in 2014

Question 22

What is the prevalence of a disease dependent on?

Answer 22

The incidence, i.e. how quickly new cases develop
How long the disease lasts due to deaths or recovery

Question 23

What is incidence a measure of that prevalence is not?

Answer 23

Risk (gold standard when comparing diseases)

Question 24

What is way of estimating incidence? (there is a relationship but the equation is not true)

Answer 24

Prevalence/Duration of infection (time)

Question 25

What is a variable?

Answer 25

Something that we are interested in that varies

Question 26

What is a response/dependent variable?

Answer 26

The variable that we expect to be influenced by other variables

Question 27

What is a predictor/independent variable?

Answer 27

The variables that change our response variable

Question 28

What is a risk factor?

Answer 28

A variable which is associated with an increase in a disease

Question 29

What ways can associations between risk factors and disease incidence be measured?

Answer 29

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

Question 30

How can statistical association be measured?

Answer 30

Chi-square test (χ²)

Question 31

How is the risk ratio (RR) calculated?

Answer 31

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

Question 32

What does it mean when RR = 1?

Answer 32

Risk in exposed is equal to risk in non-exposed (no association)

Question 33

What does it mean when RR > 1?

Answer 33

Risk in exposed is greater than risk in non-exposed (positive)

Question 34

What does it mean when RR < 1?

Answer 34

Risk in exposed is less than risk in non-exposed (negative)

Question 35

How is the odds ratio (OR) calculated?

Answer 35

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

Question 36

What does it mean when OR = 1?

Answer 36

Odds in exposed is equal to odds in non-exposed (no association)

Question 37

What does it mean when OR > 1?

Answer 37

Odds in exposed is greater than odds in non-exposed (positive)

Question 38

What does it mean when OR < 1?

Answer 38

Odds in exposed is less than odds in non-exposed (negative)

Question 39

What do RR and OR tell us?

Answer 39

How strong the association between disease and exposure
A measure of effect is useful to evaluate causality

Question 40

What is attributable risk?

Answer 40

The amount of disease attributable to an exposure in those exposed
Sometimes reported as a proportion (e.g 200 of the 230/1000 cases of lung cancer are due to cigarette smoking)

Question 41

How is attributable risk calculated?

Answer 41

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

Question 42

Why is attributable risk useful?

Answer 42

Allows us to evaluate potential for prevention

Question 43

What is population attributable risk (PAR)?

Answer 43

The amount of disease attributable to an exposure in the population

Question 44

How is population attributable risk calculated?

Answer 44

Attributable risk x prevalence of exposure in population

Question 45

What does PAR measure?

Answer 45

Potential impact of control measures in a population, and is relevant to decisions in public health

Question 46

What is PAR useful for?

Answer 46

Determining allocation of resources