POPH192 - Lecture 18

Question 1

what does a measure of association do?

Answer 1

it quantifies the relationship between exposre/outcome among the two groups

Question 2

what are the 3 measures of association?

Answer 2

• relative risk
• risk difference
• odds ratio

Question 3

what is the equation for relative risk?

Answer 3

RR= incidence in exposed / incidence in unexposed

Question 4

what are the rules for incidence when doing the calculations?

Answer 4

you can use either IR or IP, but you have to use the same type in the numerator and denomenator

Question 5

what does relative risk tell us?

Answer 5

tells us the strength of association
- how closely linked the exposure is to the outcome

Question 6

when RR>1?

Answer 6

there is a greater likelihood of the outcome in the exposed group
- risk factor if outcome is bad (e.g. disease or mortality)

Question 7

when RR=1

Answer 7

• the null value
• no association between exposure and outcome
• incidence in exposed group and unexposed group is the same

Question 8

when RR<1?

Answer 8

• there is a greater likelihood of the outcome in the unexposed group
• exposure is protective factor if outcome is bad
• e.g. doing exercise to prevent heart attack (decreases likelihood of outcome)

Question 9

what is the equation for relative difference?

Answer 9

RD = incidence in exposed - incidence in unexposed

Question 10

what does the risk difference tell us?

Answer 10

tells us how much of the outcome is due to the exposure
and how much disease we would prevent by removing the exposure

Question 11

when RD > 0?

Answer 11

greater likelihood of outcome in the exposed group
- risk factor if outcome is bad

Question 12

when RD = 0?

Answer 12

• Null value
• no association between exposure and outcome

Question 13

when RD < 0?

Answer 13

• greater likelihood of the outcome in the unexposed group
• protective factor if outcome is bad

Question 14

what is the generic interpretation for relative risk?

Answer 14

the exposed group were XX.X times as likely to develop the outcome compared to comparison group

Question 15

what is the generic interpretation for relative difference?

Answer 15

there was an extra X cases per 100 people/per 100 person years in exposed group compared to unexposed group

Question 16

what is the odds ratio?

Answer 16

measure of association for case control studies only

Question 17

what does odds ratio tell us?

Answer 17

an approximation for relative risk

Question 18

what is the easy equation for odds ratio?

Answer 18

OR = (exposed cases/unexposed cases) / (exposed controls/unexposed controls)

Question 19

when OR>1?

Answer 19

exposure may be a risk factor for the disease

Question 20

when OR=1?

Answer 20

• null value
• no association between exposure or outcome

Question 21

when OR<1?

Answer 21

• exposure may be a protective factor for disease
• decreased chance if getting outcome if you have the exposure

Question 22

what is the interpretation of odds ratio?

Answer 22

the exposed group were XX.X time as likely to develop the outcome compared to the comparison group