Lecture 18 Measures of association

Question 1

How do we know something is a determinant of an outcome
Associated with an outcome
How we know those (4x 5x something)

Answer 1

Measures of association

Question 2

Analytic epidemiology (how we get to those)

Answer 2

Importance of comparison groups In Particular what they represent
PECOT & GATE (use to calculate measures of association)

Question 3

Measures of association

Answer 3

Relative risk (4 or 5x greater risk of astronauts dying from heart attacks)

Question 4

Association between exposure and outcome
Astronaut
CVD
43%

Answer 4

Exposure
- Whether Astronaut is related to cardiovascular disease

Outcome
- Cardiovascular disease

43%
- Lunar astronauts died from CVD

comparison group

Question 5

Best way to determine whether or not the exposure is likely to be a determinant of outcome

Answer 5

• Compare people with exposure with a comparison group

- Whether incidence is greater or lower in the exposed group

Question 6

How do we find associations?

Answer 6

Through analytic study designs

using PECOT and GATE

Question 7

what does PECOT stand for?

Answer 7

Population - group of people in study

Exposure - what the potential determinant is

Comparison - what the potential determinant being compared to

Outcome - health outcome being assessed

Time - how long people are being followed up

Question 8

GATE frame

Answer 8

Population
Exposure / Comparison
Outcome

Question 9

Source vs sample population

Answer 9

Source - Population the sample is recruited from

Sample - Population included in your study

Question 10

Exposure / comparison circle

Answer 10

Exposed group (top)
Comparison group (bottom)

Question 11

Outcome square

Answer 11

People who get

People who dont

Question 12

Measures of association

Answer 12

Relative measure

Whether the group is higher in the exposed than not

Question 13

Relative risk

Answer 13

Incidence exposed / Incidence comparison

Question 14

Null value RR

Answer 14

• 1
• Same incidence of outcome
• no association between exposure and outcome
• Equal likelihood of outcome in both group
• Exposure doesn’t change likelihood of outcome,

Question 15

Risk factor RR

Answer 15

• Greater incidence of outcome in exposed group
• Greater likelihood of outcome in exposed group
• If outcome bad, exposure is a risk factor for the outcome

Question 16

if relative risk above 1

would exposure be a risk factor or a protective factor for the outcome?

Answer 16

risk factor

Question 17

Protective factor RR

Answer 17

• Greater incidence of outcome in comparison group
• Greater likelihood of outcome in comparison group
• If outcome bad, exposure is
  a protective factor for the outcome
• Decrease risk of having bad outcome

Question 18

if relative risk below 1

would exposure be a risk factor or a protective factor for the outcome?

Answer 18

protective factor

Question 19

Interpret relative risk

Answer 19

Exposed group
Value (as likely)
Outcome
comparison

• X times as likely

Question 20

Using gate to calculate relative risk

Answer 20

Ie / Ic

no units

need to use same incidence (rate or proportion)

Question 21

Incidence rate calculation conclusion

Answer 21

Epidemiologists in NZ 2.5 times as likely to receive abusive mail than non epidemiologists

Question 22

RR

Answer 22

How many times as likely more or less times likely the outcome is in exposed vs the comparison group

Question 23

risk difference / attributable risk

Answer 23

Differences in the incidences:

Ie - Ic

How many extra/fewer cases of the outcome in the exposed group are attributable to the exposure?

Question 24

Null Value RD

Answer 24

Ie = Ic
RD = 0
No association

Question 25

Incidence in exposed and comparison group the same

Answer 25

Null value

Question 26

Risk factor

Answer 26

Ie > Ic

RD > 0

Question 27

Protective factor

Answer 27

Ie < Ic

RD < 0

Question 28

Incidence in exposed greater than the comparison group

Answer 28

Risk factor

Question 29

Incidence in exposed less than the comparison group

Answer 29

Protective factor

Question 30

Risk difference units

Answer 30

Same as incidence rate

Eg 15 cases per 100 over 10 years

Question 31

RR vs RD

Answer 31

RR

• Clues to aetiology (causes)
• Strength of association

RD

• Impact of exposure
• Impact of removing exposure

Question 32

How far away the number is from the null value

Further from null

Answer 32

stronger the association

Question 33

How do we know if an exposure is associated with an outcome?

Answer 33

Compare development of outcome in people with the exposure with development of outcome in people without the exposure

Question 34

How do we know if an exposure is associated with an outcome? quantify with

Answer 34

measure of association

Question 35

what does PECOT/GATE help us understand?

Answer 35

this logic by highlighting the fundamental characteristics of analytic epidemiological studies

Question 36

PECOT/GATE

Answer 36

Makes explicit the logic of comparing

Describes key components of a study

Can use GATE to calculate measures of occurrence and association

Question 37

Compares quantify association using

Answer 37

measures of association

Question 38

what are some measures of association

Answer 38

RR

RD

Question 39

How do you calculate RR?

Answer 39

I exposed / I comparison

Question 40

measures of association

RR

Answer 40

times as likely
exposed group to develop outcome than the comparison group

null value = 1

Question 41

how do you calculate RD?

Answer 41

I exposed - I comparison

Question 42

measures of association

RD

Answer 42

extra / fewer cases of outcome in exposed group are attributable to exposure

null value = 0