Why EBM

1. Large trials provide evidence that drug/procedure/test works
2. Thalidomide withdrawn due to actions of Francis Kelly we discovered that improper informed consent practices were occurring with the use of thalidomide -> caused birth defects
3. Pharmaceu

Types of Study Designs

Hierarchy of Clinical Evidence

Some Researchers Could Copy Countless Cases In Alaska

RCT Procedure

1. Studies an appropriate sample of a patient spectrum from the patient population
2. Randomized to experimental exposure or no/control exposure
3. Evaluated to outcome, can be measured multiple times

RCT Advantages

1. Unbiased distribution of confounding factors
2. Blinded
3. Randomization facilitates fair statistical analysis

RCT Disadvantages

1. Expensive
2. Time consuming
3. Volunteers needed, creating bias
4. Ethically problematic at times

Cohort Study Procedure

1. Studies an appropriate sample of patient spectrum from the patient population
2. Exposure has already occurred, patient assigned to group dependent upon their exposure
3. Evaluated for outcome, can be measured multiple times

Cohort Study Advantages

1. Ethical
2. Subjects can be matched
3. Can establish timing and directionality

Cohort Study Disadvantages

1. Controls may be difficult to identify
2. Exposure can be linked to a hidden confounded
3. Blinding is difficult
4. Randomization is not present
5. For rare diseases, need large sample size or long follow-ups