Lecture 3, part 2

Question 1

For what measures can odds ratios be calculated?

Answer 1

Either incidence or prevalence

Question 2

In what type of studies can ORs and RRs be calculated?

Answer 2

ORs can be calculated in cohort studies and case-control studies
Risk ratios can only be calculated in a cohort or experimental study

Question 3

When is odds ratio a good estimate of risk ratio?

Answer 3

The “cases” studied are representative of all ppl with the dz in the pop from which the cases were drawn, with regard to hx of the exposure
The “controls” are representative of all ppl without the dz in the pop from which the cases are drawn, with regard to hx of exposure
When the dz under study is infrequent (rare)

Question 4

Definition of absolute effects/difference measures

Answer 4

Measures the excess dz risk attributable to the exposure (excess risk in the exposed group compared to the unexposed group)

Question 5

How to calculate absolute effects/difference measures

Answer 5

Compare dz occurrence among the exposed with the dz occurrence among the unexposed comparison group by subtracting one from the other

Question 6

When is risk difference = 0?

Answer 6

When there is no association

Question 7

Purpose of absolute effects/difference measures

Answer 7

Gives info on PH impact of an exposure
-How much dz would be prevented if exposure were removed?

Question 8

Risk difference formula

Answer 8

RD = incidence in exposed - incidence in unexposed

Question 9

Definition of population risk difference

Answer 9

Measures excess dz occurrence among the total pop that is associated with the exp

Question 10

What impact is measured in population risk difference?

Answer 10

Impact of the exposure not only on the exposed but also on the total pop

Question 11

Purpose of population risk difference

Answer 11

Helps to evaluate which exposures are most relevant to the health of a target population

Question 12

Population risk difference formula

Answer 12

PRD = RD(Pexp)
where Pexp is the proportion of the pop that is exposed
or
PRD = Rtotal - Runexposed
where Rtotal is the risk/rate in the total pop and Runexp is the risk among the unexposed

Question 13

On what is population risk difference dependent?

Answer 13

The prevalence of the exposure or risk factor
A weak RF that is prevalent could account for more dz in a pop than a strong RF that is rare

Question 14

Definition of attributable proportion among the exposed

Answer 14

The proportion of dz among the exposed that would be eliminated if the exp were eliminated

Question 15

What is assumed in attributable proportion among the exposed?

Answer 15

Causal relationship btwn exp and dz

Question 16

Formula of attributable proportion among the exposed

Answer 16

APexp = (Rexp - Runexposed)/Rexp

Question 17

Definition of attributable proportion among the total pop

Answer 17

The proportion of dz in the total pop that would be eliminated if the exp were eliminated

Question 18

Formula for attributable proportion among the total pop

Answer 18

APtot = (Rtot - Runexp)/Rtot

Question 19

On what does choice of measure depend?

Answer 19

Purpose of analysis
Sometimes no choice…ratio must be used if absolute rates are not directly estimable

Question 20

When are risk difference measures useful?

Answer 20

Estimation of the magnitude of a PH problem attributable to an exp

Question 21

When are risk ratio measures more informative?

Answer 21

About the strength of an association which is the usual measure for etiologic research

Question 22

What should be used when you can’t calculate incidence directly?

Answer 22

Odds ratio

Question 23

On what are crude rates based upon?

Answer 23

Raw data

Question 24

When are crude rates difficult to interpret?

Answer 24

When the compared groups differ based on some characteristic (factor) that affect the rate of dz

Question 25

What are common factors that distort results based on crude data?

Answer 25

Age
Sex
Race/ethnicity

Question 26

What will yield a more accurate representation of actual rate differences?

Answer 26

Side-by-side comparisons stratified by levels of the characteristic

Question 27

What is an alternate method to crude rates?

Answer 27

Calculate adjusted or standardized rates