Lectures 8-10

Question 1

Relative differences

Answer 1

Dividing frequencies, proportions, or counts

Question 2

Which will ALWAYS be larger? Absolute or relative differences?

Answer 2

Relative

Question 3

Why do studies often use relative differences instead of absolute differences?

Answer 3

Relative differences are always larger. Saying something has a 50% relative difference compared to something is more eye catching than saying it has a 10% absolute difference.

Question 4

(T/F) Relative differences are the more representative statistic when compared to absolute differences.

Answer 4

False. Absolute differences are more representative.

Question 5

Risk, Incidence Risk (IR), Attack Rate

Answer 5

Probability of outcome in exposed and non exposed.

A)/(A+B
(C)/(C+D)

Question 6

Risk Ratio (RR), Relative Risk

Answer 6

Risk in Exposed/Risk in Unexposed

[(A)/(A+B)] / [(C)/(C+D)]

Question 7

Interpret: RR=1.0 (Group A/Group B)

Answer 7

No difference in risk between two groups

Question 8

Interpret: RR=1.53 (Group A/Group B)

Answer 8

Group A has 53% greater risk than Group B.

Question 9

Interpret: RR=6.18 (Group A/Group B)

Answer 9

Group A has 6x greater risk than Group B

Question 10

Intepret: RR = 0.73 (Group A/Group B)

Answer 10

Group A has 27% lower risk than Group B.

Question 11

If risk in Forest Plot is:

1. Left of RR=1
2. Right of RR=1

Answer 11

1. Left is decrease from control

2. Right is increase from control

Question 12

Absolute Risk Reduction (ARR) a.k.a. Attributable Risk (AR)

Answer 12

The difference in risk (subtraction) between the exposed and unexposed that can be attributed to to the actual exposure.

Question 13

Exposed Risk = 14%
Unexposed Risk = 17.8%
What is ARR?

Answer 13

ARR = 3.8%

Question 14

Relative Risk Reduction (RRR)

Answer 14

(ARR)/(R in unexposed)

Question 15

Exposed Risk = 14%
Unexposed Risk = 17.8%
ARR = 3.8%
RRR = ?

Answer 15

RRR = (ARR)/Risk in unexposed
RRR = 3.8/17.8
RRR = 21.3%

Question 16

Which is always higher? ARR or RRR?

Answer 16

RRR

Question 17

Number Needed to Treat (NNT)

Answer 17

1/ARR

Question 18

ARR=3.8% or 0.038

NNT = ?

Answer 18

NNT = 1/0.038 = 26.32

Needed to treat 27 patients to experience the study outcome.
For every 27 patients, one will have outcome.

Question 19

If good outcome do you want small or large NNT?

Answer 19

Small NNT; Treat less people to get good results; Higher ratio of good results

Question 20

If bad outcome do you want small or large NNT?

Answer 20

Large NNT; Want to treat many people to get one bad outcome; Small ratio of bad outcomes

Question 21

Odds:

                        Outcome                            Exposure     Cases      Controls     Total Yes                   A                B           A+B No                   C                 D          C+D Total               A+C           B+D      A+B+C+D

Answer 21

Odds of exposure in cases and controls

A/C
B/D

Question 22

Odds Ratio (OR)

Answer 22

Odds of exposure in cases vs. odds of exposure in controls

A/C)/(B/D) or (A x D)/(B x C

Question 23

What 3 things could be incorrect in the wrong answer choices for RR/OR/HR?

Answer 23

1. Direction of words (increase or decrease)
2. Magnitude (correct numbers)
3. Group Comparison

Question 24

Absolute Differences

Answer 24

Subtracting frequencies or counts