Evidence Based Medicine

Question 1

What is a controlled trial?

Answer 1

The intervention is being compared to something else: a placebo, a gold-standard, best practice

Question 2

What is a randomised trial?

Answer 2

The population receiving the intervention and the population being compared are only different because of random variation

Question 3

2 reasons to randomise?

Answer 3

To prevent differences between groups at the outset affecting the outcome

To reduce bias

Question 4

Examples of inclusion criteria?

Answer 4

Likely to benefit from treatment
     Definitely has the disease
     Patient is likely to respond
Unlikely to be harmed
     No known adverse reactions/ contraindications

Question 5

Examples of exclusion criteria?

Answer 5

Patient unlikely to adhere to treatment or complete the follow-up

Question 6

Name some ‘controls’ that could be used?

Answer 6

Placebo
Nothing
Current best practice
etc.

Question 7

Name some ‘outcome measures’ that could be used?

Answer 7

Death
Clinical measurement
Symptoms
QoL

Question 8

Some criteria for outcome measures’?

Answer 8

Relevant
Easily measured
Accurate

Question 9

Rank these levels of evidence, low to high?
Systematic reviews
Case-control studies
Randomised controlled trials
Cohort studies

Answer 9

Systematic reviews
Randomised controlled trials
Cohort studies
Case-control studies

Question 10

What is the p value?

Answer 10

A numerical value indicating the probability that this observation has occurred due to chance
Between 0 and 1

Question 11

What is a confidence interval?

Answer 11

A way of indicating a range of values which probably contain the “true” value

Question 12

What is a Type 1 error?

Answer 12

when results are due to chance, not due to actual difference in e.g. treatments tested

Question 13

What is the null hypothesis?

Answer 13

States there is no difference between 2 groups

(study starts by predicting that results will be the same in both groups (control and other)– used as a marker to see how significant the findings are)

Question 14

In a critical appraisal, we assess internal and external validity- what do they mean?

Answer 14

Internal validity- does the study measure what it sets out to measure? good methods?

External validity- can the results from the study be generalised to a wider population/in real life?

Question 15

What is a case-control study?

Answer 15

Starts with selecting subjects based on disease- retrospective

Question 16

Pros of case-control study?

Answer 16

Rapid and cheap

Good for rare diseases/outcomes

Question 17

When interpreting results, what is important to bear in mind?

Answer 17

Statistical significance vs clinical significance

how does the result translate into clinical practise/no. of patients affected
e.g. risk before and after intervention

Question 18

Absolute risk reduction=

Answer 18

risk before-risk after

Question 19

Relative risk reduction=

Answer 19

absolute risk after / absolute risk before

Question 20

Number needed to treat=

Answer 20

1/ absolute risk reduction

Question 21

What does qualitative research use?

Answer 21

meanings, experiences and views

Question 22

What is inductive logic?

Answer 22

Building knowledge from the bottom up through observations of the world- develop new laws/theories

Question 23

What is deductive logic?

Answer 23

Starts with a theory from which a hypothesis is derived and applied to observations about the world. Theory is confirmed (strengthened) or rejected (weakened)

Question 24

When analysis qualitative data, what should be done?

Answer 24

Identify major recurrent themes then chart

Question 25

6) 360 pts participated in RCT designed to compare effectiveness of drug x in reducing deaths vs placebo – out of 120 pts in treatment group 12 died in 3 yrs; out of 240 pts in control 48 pts died within 3 years
Which of the following measures for risk of death within 3 yrs is true?

Event rate in control is 0.3
Event rate in treatment is 0.2
relative risk of treatment compared with control is 0.25
Relative risk reduction is 67%
NNT to prevent 1 death is 10

Answer 25

Answer: Nnt to prevent 1 death is 10

Event rate in control= 48/240= 0.2
Event rate in treatment= 12/120= 0.1

RR= 0.1/0.2= 0.5
RR reduction= (0.2- 0.1)/0.2 = 50%

NNT= 1/ absolute risk reduction= 1/(0.2-0.1)= 10

(0.2-0.1) = absolute risk reduction

Question 26

Features of cohort study?

Answer 26

Recruitment + followed up over time

Compare exposed vs non-exposed