Measures of Effect

Question 1

Which ratios are relative measures of effect?

Answer 1

Risk Ratio & Odds Ratio

Question 2

What is the definition of relative measures of effect?

Answer 2

They describe how an exposure changes the risks or odds of an outcome compared to the risks and the odds of an unexposed group

Question 3

Which are the examples of absolute measures of effect?

Answer 3

Absolute risk
Number needed to treat

Question 4

What is the calculation of risk ratio/relative risk?

Answer 4

Risk of exposed/Risk of unexposed

Question 5

What is the interpretation of a RR < 1?

Answer 5

The risk of a certain outcome is lower in the exposed group than it is in the unexposed

Question 6

What is the interpretation of RR > 1?

Answer 6

The risk of a certain outcome is higher in the exposed group compared to the unexposed group; exposure is a risk factor for the outcome

Question 7

What is the interpretation of a risk ratio = 1?

Answer 7

This means there is no difference at all between the risk of the exposed vs. the unexposed groups

Question 8

What is a confidence interval?

Answer 8

It is the range with whichin the actually risk ratio lies in with a probability of 95%

Question 9

When is the difference between two groups statistically significant?

Answer 9

If the confidence interval does not include 1

Question 10

What is the definition of risk?

Answer 10

The probability of an outcome which can be both positive or negative

Question 11

How would you interpret an RR of 1.5?

Answer 11

The risk of the exposed group getting affected is 1.5 times greater than the risk of unexposed people getting affected, or 50% higher

Question 12

What is the calculation for relative risk difference?

Answer 12

Risk Ratio - 1

Question 13

What is absolute risk difference?

Answer 13

Risk of exposed group - Risk of unexposed group

Question 15

What is the calculation for Odds Ratio?

Answer 15

Odds of exposed group/ Odds of unexposed group

Question 16

What is the Odds Ratio?

Answer 16

Relative measure of effect

Question 17

What is the definition of “Odds”?

Answer 17

The chance of having a certain outcome

Question 18

What is the interpretation of OR < 1?

Answer 18

The chance of a certain outcome is lower in exposed group

Question 19

What is the interpretation of OR > 1?

Answer 19

The chance of a certain outcome is greater in the exposed group

Question 20

What is the interpretation of OR = 1?

Answer 20

There is no difference for the chance of a certain between an exposed group vs an unexposed one

Question 21

When does the CI of Odds Ratio show statistical significance?

Answer 21

When the Odds Ratio does not contain 1

Question 22

What is the difference between risks and odds calculations?

Answer 22

To find the risk of an outcome –> people with an outcome/all people

To find the odds of an outcome –>
people with an outcome/people WITHOUT an outcome

Question 23

What are the differences between RR and OR?

Answer 23

OR –> all study types, more often used for case-control
RR –> cannot be used for case-control studies

Interpretation of RR is easier than OR, so RR is preferred

Question 24

In which cases are RR and OR very similar?

Answer 24

When the outcome is really rare

Question 25

What is the number needed to treat calculation?

Answer 25

1/absolute risk difference

Question 26

What is the definition of number needed to treat?

Answer 26

Number of people you need to treat in order to help one person

OR

Number of people that need to be exposed to a treatment or risk factor for one single outcome to occur that would not be otherwise occurring

Question 27

What is the purpose of the number needed to treat?

Answer 27

To measure the benefit of a treatment

Question 28

In terms of a treatment (medication) what does a low NNT indicate?

Answer 28

Treatment is very effective –> very few people need to take the medicine in order to see an improvement

Question 29

What is the difference between the number needed to treat vs the number needed to harm?

Answer 29

The number needed to harm indicates that the exposure has a negative effect on the group

Question 30

What is the survival function?

Answer 30

The probability of exposed or unexposed group surviving past a specific time period (for instance; number of years)

Question 31

What is the calculation of the survival function?

Answer 31

Number of patients surviving longer than t/ total number of patients

where t = a specific time period

Question 32

What is the hazard function?

Answer 32

The probability of dying in the next few seconds, given that they are alive now, past the survival function

Question 33

What is the purpose of the Kaplan Meier Plot?

Answer 33

It allows us to make statements on the survival rate based on time

Question 34

Is Kaplan Meier Plot parametric or non-parametric?

Answer 34

Non-parametric model

Question 35

What is the difference between a parametric and a non-parametric model?

Answer 35

Non-parametric tests are not seriously affected by outliers