Classes #8-#10: Measures of Association

Question 1

In what kind of study is risk ratio/ relative risk (RR) used?

Answer 1

Customarily used in studies where subjects are allocated based on exposure (y/n) and evaluated for disease (outcome).

**Example: cohort studies

Question 2

How do you calculate risk (incidence risk (IR)) for both the exposed and non-exposed?

Answer 2

Risk of OUTCOME in “exposed” = A / (A+B)

Risk of OUTCOME in “non-exposed” = C / (C+D)

Question 3

What is the risk ratio (RR) and how do you calculate it?

Answer 3

The RR is the ratio of the risk from 2 different groups.

RR = risk in exposed / risk in non-exposed

Question 4

What are the 3 major ratios in research?

Answer 4

Risk Ratio (RR) 
Odds Ratio (OR)
Hazard Ratio (HR)

Question 5

What are the 3 things that you should look for when interpreting ratio’s (RR/OR/HR)?

Answer 5

1) direction of words (increased or decreased)
2) Magnitude
3) group comparison

Question 6

What does the absolute risk reduction (ARR) tell you and how is it calculated?

Answer 6

ARR defines the risk difference in the outcome among “exposed” that can be “attributed” to the actual exposure.

RRR = Risk in “non-exposed” - risk in “exposed”

Question 7

How do you calculate the relative risk reduction (RRR)?

Answer 7

RRR = ARR / R-unexposed

Question 8

How do you interpret number needed to treat and how is it calculated?

Answer 8

Interpretation: number of (whole) patients needed to be treated to experience the studied event outcome.
– outcome event can be a BENEFICIAL or HARMFUL event

NNT or NNH = 1 / ARR

Question 9

What kind of study is the odds ratio (OR) typically used for?

Answer 9

OR is customarily used in studies where subjects are allocated based on disease presence (y/n) and evaluated for exposure.
–example: case-control studies

Question 10

What does the calculation: A/C give?

What does the calculation: B / D give?

Answer 10

The odds of exposure vs. odds of NOT being exposed (in cases)

The odds of exposures vs. odds of NOT being exposed (in controls)

Question 11

How do you calculate the Odds Ratio (OR)?

Answer 11

OR = [(A/C) / (B/D)]

Question 12

What is the property in the ratio’s RR, OR, and HR is the ratio is 1.0?

Answer 12

Then the event (or outcome) is equally likely for both groups.
- if “ratio” is >1.0 then the event (outcome) is more likely to occur in the main study (comparison) group

 - if "ratio" is

Question 13

True or False:

Absolute differences will always be smaller than relative differences.

Answer 13

True