Module 6

Question 1

Confounding

Answer 1

the mixing of the effect of the exposure with the effect of another factor (the confounder) which distorts the estimated measure of association
a confounder is a factor that can be
a risk factor for the disease of interest independent of the exposure
associated with the exposure of interest
not a consequence of the exposure

Question 2

Failure to account for a confounder

Answer 2

wipe-out an association
create an invalid association
reverse the direction of association
change the degree of association

Question 3

Causal pathway

Answer 3

X leads to Y which leads to Z
X = exposure variable
Y = variable in causal pathway
Z = disease variable

Question 4

Strategies for handling confounding

Answer 4

randomization
restriction = limit entrance to subjects who fall in one category of the confounder
matching = only include controls with comparable characteristics to cases
multivariable regression analysis = add confounding variables into regression models
stratification = separate ORs or RRs by different levels of a confounder

Question 5

Identifying confounders

Answer 5

literature search = suggests potential confounders for which data should be collected
biologic plausibility
this changes
not all confounders known
results unknowingly biased

Question 6

Effect modification

Answer 6

when the magnitude of the effect of the primary exposure of an outcome differs depending on the level of a third variable
effect modification vs confounding
effect modification is a biological phenomenon in which the exposure has a different impact in different circumstances
confounding is a form of bias

Question 7

Confounding graphs

Answer 7

parallel lines indicate confounding
effect of exposure on disease is the same at different levels of the confounder
stratum-specific ORs or RRs are equal
assuming the association is linear
ORs/RRs = 1 = lines are horizontal
ORs/RRs > 1 = lines have an upward slope
ORs/RRs < 1 = lines have downward slope

Question 8

Effect modification graphs

Answer 8

non-parallel lines indicate effect modification
exposure-disease association differs at different levels of the effect modifier
negative association = downward sloping
positive association = upward sloping

Question 9

Mantel-haenszel estimator

Answer 9

crude OR/RR falls outside range of stratum-specific ORs/RRs
Mantel-Haenszel estimator measures the average effect of exposure across all strata
advantage = easy to compute with a calculator
disadvantage = computation difficulty increases as tables get bigger

Question 10

Confounder and effect modifier possibilities

Answer 10

a confounder = compare crude and Mantel-Haenszel
if the values are different, then it is a confounder
an effect modifier = compare stratum 1 and stratum 2
if the values are different, then it is an effect modifier
a confounder and an effect modifier
neither a confounder nor an effect modifier