Interaction and Mediation

Question 1

Define synergism

Answer 1

The action of separate
substances that in combination produce an
effect greater than that of any component
taken alone, describes biological mechanisms
of action i.e. smoking and asbestos

Question 2

The relative risk of ischemic stroke for non-whites
compared with whites is about 2 (95%CI:1.02-2.06) for
those aged 35 to 64 years and about 1 (95%CI: 0.93-
1.02) for those 65 years of age and above. This is best
described as:
a. confounding of the effect of race by age
b. modification of the effect of race by age
c. elimination of the effect of race by age-adjustment
d. elimination of the effect of age by race-adjustment
e. all of the above

Answer 2

b. modification of the effect of race by age. Not elimination of effect because it is a regular comparison, not a stratification

Question 3

Additive interaction formula

Answer 3

(RR11 – 1) = (RR10 – 1) + (RR01 – 1)
or
R11-R00 = (R10-R00) + (R01 – R00)

Question 4

Additive interaction definition

Answer 4

Overall risk when both factors are present
= sum of the individual risks or additivity
of the individual risks

Question 5

Cole’s T index for additive interaction

Answer 5

T = R11 – R10 – R01 + R00 = 0

Question 6

Multiplicative interaction definition

Answer 6

NO interaction on multiplicative scale or
RR11 = RR10 X RR01 or
LnRR11 = LnRR10 + LnRR01
Which represents additivity of the natural logs of the risk ratios