Applied statistics and interpreting results

Question 1

Types of data used/found in clinical trials

Answer 1

Binary- two types of responses (yes/no)

Continuous- blood pressure, cholesterol

Time-to-event- death, pregnancy

Question 2

What is categorical data

Answer 2

Nominal (categories unordered)
Ordinal (categories ordered)

Question 3

Describe nominal data

Answer 3

Gives averages and means
Discrete- finite values possible
Continuous- all values are possible (decimals)

Question 4

Parametric vs non-parametric testing

Answer 4

Parametric= assume normal distribution, give significant result more often

Non-parametric= compare rank order, not influenced by outliers

Question 5

What is a null hypothesis

Answer 5

No difference exists in treatment A and B
Nothing happens

Question 6

What is the alternate hypothesis

Answer 6

Difference exists between treatment A and B

Question 7

Describe type 1 error alpha

Answer 7

False positive
Falsely rejecting Ho and detecting a significant difference when there is no difference

Question 8

Describe type 2 error beta

Answer 8

False negative
Falsely accept Ho and not notice a difference when there is a difference

Question 9

What is power (1-beta)

Answer 9

Probability of correctly rejecting Ho and detecting difference when difference exists.
Higher the power, the better.

Question 10

How to measure the effect of binary date

Answer 10

Risk difference (absolute risk difference)
Relative risk
Odds ratio
Number needed to treat
Number needed to harm

Question 11

What is absolute risk

Answer 11

Absolute risk difference - difference between risk of event in intervention and control group

Absolute risk reduction- treatment is effective and reduces unwanted event

Absolute risk increase- treatment does not work, increased risk of event

Question 12

What is NNT

Answer 12

Number needed to treat

Number of patients needed to be treated to produce one additional successful outcome

Compare efficacy of treatments

NNT= 1/ARR

Best for comparing treatment with placebo

Question 13

What is NNH

Answer 13

Number needed to harm

Number of patients needed to be treated to produce one ADR

Question 14

What is relative risk

Answer 14

AKA risk ration, risk of event occuring
1.0 is middle number
Lower= death
Higher= cure

Question 15

What is odds ratio

Answer 15

Probability of event occuring over risk of event not occuring

Question 16

What is selection bias

Answer 16

Choosing people to under/overrepresent a study
Not true representation of population

Question 17

What is attrition bias

Answer 17

Selective dropout of participants who differ from others.
E.g. those experiencing ADR

Question 18

What is P value

Answer 18

Probability by chance

Stat sig= P<0.05
How often chance gives favourable results

Question 19

What is the confidence interval

Answer 19

Estimate of the precision of results
95% CI = range of values within which we are 95% confident the true population estimate lies

Narrower CI indicates precise and reliable results

Question 20

What is a significant result in relation to CI

Answer 20

Sig if CI does not cross null value

> 1 for RR
0 for ARR

Question 21

Statistical significance vs clinical significance

Answer 21

Stat= size of effect and 95% CI in relation to Ho (no diff between treatment and control)

Clin= size of effect and 95% CI in relation to a minimum effect considered to be important

Question 22

What is intention to treat in RCT

Answer 22

Final analysis is more robust if all patients are included (even those who didn’t complete)