Evidence Based Medicine Flashcards
What is a controlled trial?
The intervention is being compared to something else: a placebo, a gold-standard, best practice
What is a randomised trial?
The population receiving the intervention and the population being compared are only different because of random variation
2 reasons to randomise?
To prevent differences between groups at the outset affecting the outcome
To reduce bias
Examples of inclusion criteria?
Likely to benefit from treatment
Definitely has the disease
Patient is likely to respond
Unlikely to be harmed
No known adverse reactions/ contraindicationsExamples of exclusion criteria?
Patient unlikely to adhere to treatment or complete the follow-up
Name some ‘controls’ that could be used?
Placebo
Nothing
Current best practice
etc.
Name some ‘outcome measures’ that could be used?
Death
Clinical measurement
Symptoms
QoL
Some criteria for outcome measures’?
Relevant
Easily measured
Accurate
Rank these levels of evidence, low to high? Systematic reviews Case-control studies Randomised controlled trials Cohort studies
Systematic reviews
Randomised controlled trials
Cohort studies
Case-control studies
What is the p value?
A numerical value indicating the probability that this observation has occurred due to chance
Between 0 and 1
What is a confidence interval?
A way of indicating a range of values which probably contain the “true” value
What is a Type 1 error?
when results are due to chance, not due to actual difference in e.g. treatments tested
What is the null hypothesis?
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)
In a critical appraisal, we assess internal and external validity- what do they mean?
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?
What is a case-control study?
Starts with selecting subjects based on disease- retrospective
Pros of case-control study?
Rapid and cheap
Good for rare diseases/outcomes
When interpreting results, what is important to bear in mind?
Statistical significance vs clinical significance
how does the result translate into clinical practise/no. of patients affected
e.g. risk before and after intervention
Absolute risk reduction=
risk before-risk after
Relative risk reduction=
absolute risk after / absolute risk before
Number needed to treat=
1/ absolute risk reduction
What does qualitative research use?
meanings, experiences and views
What is inductive logic?
Building knowledge from the bottom up through observations of the world- develop new laws/theories
What is deductive logic?
Starts with a theory from which a hypothesis is derived and applied to observations about the world. Theory is confirmed (strengthened) or rejected (weakened)
When analysis qualitative data, what should be done?
Identify major recurrent themes then chart
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: 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
Features of cohort study?
Recruitment + followed up over time
Compare exposed vs non-exposed
