Study designs and levels of evidence
Reading a study: randomised trials, cohorts, case-control and cross-sectional studies and meta-analyses, relative risk, odds ratio and number needed to treat, biases and confounders, and the grading of HAS recommendations.
- 34 cards
- 3 topics
- Free
The outline, topic by topic
Each topic is weighted the way the exam weighs it.
- Concepts
- Scenarios
- Understand
A few cards from the deck
Randomised controlled trial: what is it?
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A study in which participants are allocated at random to the treatment studied or a control group.
It is the best way to prove a treatment works.
You want to look for the causes of a very rare disease. Which study design?
- A case-control study
- A general population cohort
- A cross-sectional study
- A randomised trial
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A case-control study
Starting from the few patients avoids following thousands of people to see one appear.
Double blind: what is it?
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Neither the patient nor the investigator knows who gets the treatment or the placebo.
It stops expectations from skewing the results.
Why is randomisation so powerful?
- It increases the number of patients
- It removes the placebo
- It blinds the patients
- It spreads every factor, known or unknown, evenly between the groups
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It spreads every factor, known or unknown, evenly between the groups
The groups then differ only by the treatment.
Cohort study: what is it?
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A study that follows exposed and unexposed people over time and compares how often the disease appears.
It measures a relative risk.
A new drug must prove it works. Which study design?
- A case-control study
- A double-blind randomised controlled trial
- A collection of testimonials
- A cross-sectional study
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A double-blind randomised controlled trial
Only random allocation allows the difference to be credited to the drug.