Sept 25

Question 1

What is attributable risk?

Answer 1

-how much of a disease can be attributed to exposure in an exposure group -how much of the risk (incidence) can we hope to prevent if we are able to eliminate exposure to the risk factor

Question 2

What formula would you use to answer: What proportion of the risk in exposed persons is due to exposure?

Answer 2

-AR= (incidence in exposed- incidence in unexposed)/incidence in exposed

Question 3

Explain the yellow versus blue area

Answer 3

• blue area is baseline risk shared by both exposed and unexposed groups (could be due to genetics, environment, etc.)
• “excess incidence”; yellow area is the additional risk that is conferred by the exposure (additional risk that you have from doing what you do)

Question 4

What is population attributable risk?

Answer 4

• eg: what can we hope to accomplish in the population if we got smokers to quit smoking
• PAR= (incidence in total population- incidence in unexposed group)

Need to know: incidence in exposed (smokers) and unexposed groups (non smokers), proportion of total population who does exposure (smokers in Canada)

Question 5

How to calculate incidence in total population

Answer 5

Incidence in total pop= (incidence in exposed)(%exposed in that population) + (incidence in unexposed)(%unexposed in that population)

-picture shows how to calculate percent population attributable risk

Question 6

What are differences between RR and AR/PAR?

Answer 6

• RR is used to measure the strength of an association and help assess causation (but does not say exposure x causes disease y)
• AR/PAR used to assess the potential effects of prevention programs in public health

Question 7

What is incidence density?

Answer 7

-number of cases/person time of follow up

Interpret by saying: Incidence is ___ cases of disease per ___ person-years of follow-up

-slightly more accurate when we don’t have complete follow up

Question 8

What are cross sectional studies?

Answer 8

• assess exposures and outcomes
• identifying exposure status and outcome status at the same point in time
• can’t determine temporality (no cause and effect)
• can’t calculate relative risk (some subjects will already have the disease so they don’t have risk to develop it and some subjects we aren’t following up in time to see who gets the disease)
• useful as a first look to generate hypotheses

Question 9

What can you calculate from cross sectional study?

Answer 9

-prevalence of disease in exposed/prevalence of disease in unexposed

Question 10

Strengths of cross sectional studies

Answer 10

• quick, cheap
• useful if we have hypotheses in the beginning stages, hypothesis generation, exploratory analyses

Question 11

Weaknesses of cross sectional studies

Answer 11

• reverse causality bias: E and D assessed at the same time so can’t be sure which one preceded the other
• prevalent cases may not be representative of all cases (more likely to be cases of long duration, survivorship bias: people who have lived with disease tend to be alive longer)
• don’t capture cases of disease where they die quickly

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