Interpreting Study Results

Question 1

How are results typically presented?

Answer 1

means
proportions
-simple percentages
-risk ratio
-odds ratio
time to an outcome
-survival curve
-hazard ratio

Question 2

What is the mean?

Answer 2

continuous outcomes
compare the average of the outcome between groups or change from baseline

Question 3

What are proportions?

Answer 3

the fraction of the total that possesses the outcome
compare the proportion that have the outcome between groups

Question 4

What is the absolute risk reduction (ARR) or absolute risk difference (ARD)?

Answer 4

the absolute difference between the probability of the event in the control group and probability of the event in the intervention group

Question 5

What is the relative risk (RR)?

Answer 5

dichotomous outcomes
shows what the “risk” of the outcome in the intervention group is compared to the risk in the control group
probability of event (intervention)/probability of event (control)

Question 6

What does the relative risk number tell us?

Answer 6

RR=1
-no difference in risk between groups
RR<1.0
-less risk out outcome in intervention group
RR>1.0
-higher risk of outcome in intervention group

Question 7

What is the relative risk reduction (RRR)?

Answer 7

the degree to which baseline risk is reduced (or increased) by the intervention
RRR=1-RR

Question 8

What is the odds ratio (OR)?

Answer 8

shows the odds of the outcome occurring in the intervention group compared to the control group
odds (intervention)/odds (control)

Question 9

What does the OR tell us?

Answer 9

OR=1.0
-no difference in odds between groups
OR<1.0
-less odds of outcome in intervention group
OR>1.0
-higher odds of outcome in intervention group

Question 10

What is the number needed to treat (NNT)?

Answer 10

number of subjects who would have to be treated (receive the intervention) in order for one additional subject to “benefit” in comparison to the control
NNT=100/ARD
must take into account the duration of the study

Question 11

What is the number needed to harm (NNH)?

Answer 11

number of subjects who would be treated before you see one additional subject with an adverse effect compared to control
NNH=100/ARD

Question 12

What are Kaplan-Meier survival curves?

Answer 12

compares how long it takes subjects in each group to reach the outcome
often reported as “median survival time”
-time for half the subjects to reach the outcome
-p value will tell you if theres a statistically significant difference between the groups

Question 13

What does the hazard ratio tell us?

Answer 13

HR=1.0
-no difference in hazard between groups
HR<1.0
-less hazard of outcome in intervention group
HR>1.0
-higher hazard of outcome in intervention group

Question 14

What are confidence intervals?

Answer 14

range where the true effect of the intervention (treatment) lies
the narrower the CI, the more precise the results
increase sample size=increase precision

Question 15

What can CI show us?

Answer 15

magnitude of the effect
-best case-worse-case scenario
if there is really is a difference
-if the CI crosses the threshold for “no difference”, then the results are not statistically significant
-for means/proportions: no difference=0
-for RR or OR: no difference=1

Question 16

Which is better, the 95% CI or p-value?

Answer 16

reporting CI is becoming more common/required
CI show us the range in the actual data measurements
CI shows us the direction of effect, p-value just indicates if a difference exists
CI can help distinguish between clinical and statistical significance

Question 17

Differentiate between superiority, non-inferiority and equivalence.

Answer 17

superiority:
-want to show an intervention is better than control (active/placebo)
-is there statically significant/clinically relevant difference between groups?
non-inferiority:
-is the new intervention not substantially worse than an established intervention?
equivalence:
-is the new intervention neither worse nor better than an established intervention?

Question 18

What are non-inferiority trials?

Answer 18

clinical trial to establish that an intervention is not clinically worse than a comparison by more than a pre-determined margin

Question 19

When should the non-inferiority margin be determined?

Answer 19

a priori
-prevents bias
-based on a combination of statistical reasoning and clinical judgement

Question 20

What kind of analyses should be done and reported for non-inferiority trials?

Answer 20

ITT
per protocol
confidence intervals are key

Question 21

What would happen if only ITT was reported for a non-inferiority trial?

Answer 21

it can bias towards non-inferiority if lots of participants are lost to follow-up or have protocol violations
-dont get to observe the maximal effect of the drug

Question 22

What would happen if only per protocol was reported for a non-inferiority trial?

Answer 22

problems with confounding, power, etc

Question 23

What can be done once non-inferiority is established?

Answer 23

an analysis for potential superiority can be conducted

Question 24

True or false: lack of superiority in an superiority trial design means non-inferiority

Answer 24

false
lack of superiority in a superiority trial design does not mean non-inferiority and cannot claim non-inferiority

Question 25

What is a propensity score?

Answer 25

the probability that a subject would be in a particular treatment group based on their observed baseline characteristics

Question 26

What is the goal of propensity scores?

Answer 26

mimic RCTs by balancing observed characteristics between study groups

Question 27

What do propensity scores help to reduce?

Answer 27

selection bias and confounding in observational studies

Question 28

True or false: propensity scores replace the value of randomization

Answer 28

false

Question 29

What is an adaptive clinical trial design?

Answer 29

clinical trial design that allows for prospectively planned modifications to one or more aspects of the design based on accumulating data from subjects in that trial

Question 30

What are examples of pre-planned changes for adaptive clinical trial designs? What are the benefits of these changes?

Answer 30

adjusting sample size
-prevent underpowered studies
-prevent unnecessary exposure to subjects
stopping treatments arms/groups
-prevent unnecessary exposure to useless/harmful treatment
-prevent wasting resources and time
changing allocation of subjects to study groups
-fewer subjects randomized to less beneficial/useless treatment
-more subjects receive beneficial treatment
identifying subjects who are likely to benefit and focus recruitment efforts on them
-identify subjects likely to benefit
stopping study early because of obvious benefit or harm
-prevent unnecessary exposure
-prevent wasting resources and time
-quicker dissemination of positive findings

Question 31

What do interim data analyses create the potential for?

Answer 31

operational bias