Levels of Evidence

Question 1

Meta-Analysis

Answer 1

Data combined from multiple studies with statistical analysis

Question 2

Systematic Review

Answer 2

Comprehensive review, but no stats

Question 3

Randomized Controlled Trial

Answer 3

(Level 1)
Groups randomly assigned to either a treatment or control group. Ideally, groups should be similar at the start of the experiment.
ex) Future surgical patients of yours who are willing to take aspirin or a sugar pill

Question 4

Prospective Cohort Study

Answer 4

(Level 2)
Two groups, followed over some future time. Group assignment is not random.
ex) Measuring cholesterol levels every week in students ho drink coffee vs students who do not

Question 5

Retrospective Cohort Study

Answer 5

(Level 3)
Two groups, looking back in time
Ex) Reviewing hphy 212 data for the past 3 years and comparing grades for males and females

Question 6

Case-Control Study

Answer 6

(Level 3)
Two similar groups with different outcomes are compared
Ex) A study comparing people with diabetes compared to people without diabetes to examine genetic risk factors

Question 7

Case Series

Answer 7

(Level 4)
Similar to a case report, but with multiple patients (or observations)
Ex) your next week’s surgical patients all taking aspirin

Question 8

Expert Opinion

Answer 8

(Level 5)

Asking experts what they think