Experimental Studies Randomized Trials Clinical Trials
Experimental Studies Randomized Trials Clinical Trials.
Jan 03, 2016
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Experimental StudiesRandomized Trials
Clinical Trials
Research Design Epidemiology
Descriptive StudiesCase ReportsCase SeriesCross Sectional Survey
Analytic StudiesObservational Studies
Case-Control or Case-ComparisonCohort Studies
Intervention StudiesClinical Trials
History
The Islamic-Persian scholar Avicenna (980–1037) was an early proponent of the technique. James Lind (1716–1794) ran a clinical trial in 1747 to compare the effects of cider, oranges and lemons and four other treatments in 12 patients suffering from scurvy (two assigned to each treatment). The two given oranges and lemons recovered. The first modern randomized clinical trials were carried out by the Medical Research Council in the United Kingdom and their prime mover was the statistician Austin Bradford Hill (1897–1991).
From Canon of Medicine
"The drug must be tested with two contrary types of diseases, because sometimes a drug cures one disease by Its essential qualities and another by its accidental ones." "The time of action must be observed, so that essence and accident are not confused." "The effect of the drug must be seen to occur constantly or in many cases, for if this did not happen, it was an accidental effect." "The experimentation must be done with the human body, for testing a drug on a lion or a horse might not prove anything about its effect on man."
Randomized Clinical Trials
TherapeuticAZT treatment for AIDSMastectomy vs. lumpectomy
InterventionMammography for early detectionCholesterol lowering drugs
PreventionSmoking cessationClean needle program
Strength of Evidence
Weaker Stronger
Case reports RandomizedCase series Trials
Observational studiesCase/Control
Cohort
Experimental Studies
General features inherent to methodology
prospectiveconcurrent control group intervention with placebo or usual care
investigator controls/ manipulates conditions studied (hence an experiment)investigator assigns exposure
Schematic diagram of a clinical trial
SampleNonparticipants
Randomization
ControlIntervention
Lost to follow-up
Measure outcome Measure outcome
Randomization types
SimpleSystematicBalanced blockStratified
Simple randomization
B B A B A B A A B B
B A A A A A A A B A
B A B A B B B B A B
A B A B A B B B B B
B A A A B A B B A A
A A B A B B B A B B
A B B A A B B B A B
B A A A B B A B B B
B A A B A B B B A B
B B A B B B B A B A
Systematic randomization
A B A B A B A B A B
A B A B A B A B A B
A B A B A B A B A B
A B A B A B A B A B
A B A B A B A B A B
A B A B A B A B A B
A B A B A B A B A B
A B A B A B A B A B
A B A B A B A B A B
A B A B A B A B A B
Balanced block randomization
1. AABB2. ABAB3. ABBA4. BBAA5. BABA6. BAAB
1 3 2 9 1
6 4 3 8 7
3 1 2 5 8
2 4 1 7 3
4 5 3 9 6
Balanced block randomization
1. AABB2. ABAB3. ABBA4. BBAA5. BABA6. BAAB
1 3 2 9 1
6 4 3 8 7
3 1 2 5 8
2 4 1 7 3
4 5 3 9 6
Balanced block randomization
1. AABB2. ABAB3. ABBA4. BBAA5. BABA6. BAAB
1 3 2 9 1
6 4 3 8 7
3 1 2 5 8
2 4 1 7 3
4 5 3 9 6
A A B B
Balanced block randomization
1. AABB2. ABAB3. ABBA4. BBAA5. BABA6. BAAB
1 3 2 9 1
6 4 3 8 7
3 1 2 5 8
2 4 1 7 3
4 5 3 9 6
A A B B
Balanced block randomization
1. AABB2. ABAB3. ABBA4. BBAA5. BABA6. BAAB
1 3 2 9 1
6 4 3 8 7
3 1 2 5 8
2 4 1 7 3
4 5 3 9 6
A A B B A B B A
Balanced block randomization
1. AABB2. ABAB3. ABBA4. BBAA5. BABA6. BAAB
1 3 2 9 1
6 4 3 8 7
3 1 2 5 8
2 4 1 7 3
4 5 3 9 6
A A B B A B B A
Balanced block randomization
1. AABB2. ABAB3. ABBA4. BBAA5. BABA6. BAAB
1 3 2 9 1
6 4 3 8 7
3 1 2 5 8
2 4 1 7 3
4 5 3 9 6
A A B B A B B A
A B A B
Balanced block randomization
1. AABB2. ABAB3. ABBA4. BBAA5. BABA6. BAAB
1 3 2 9 1
6 4 3 8 7
3 1 2 5 8
2 4 1 7 3
4 5 3 9 6
A A B B A B B A
A B A B
Balanced block randomization
1. AABB2. ABAB3. ABBA4. BBAA5. BABA6. BAAB
1 3 2 9 1
6 4 3 8 7
3 1 2 5 8
2 4 1 7 3
4 5 3 9 6
A A B B A B B A
A B A B A A B B
Balanced block randomization
1. AABB2. ABAB3. ABBA4. BBAA5. BABA6. BAAB
1 3 2 9 1
6 4 3 8 7
3 1 2 5 8
2 4 1 7 3
4 5 3 9 6
A A B B A B B A
A B A B A A B B
B A A B B B A A
A B B A A B B A
A A B B A B A B
B A B A A B B A
B B A A A A B B
A B B A B B A A
B A B A A B B A
B A A B A A B B
Confounding and Bias
By randomly assigning the exposure - reduce the risk of confounding because:““confounders - known and unknown” are confounders - known and unknown” are randomly distributed among the treatment randomly distributed among the treatment groupsgroups
By blinding (masking) assessment of outcomereduce the risk of information bias
Masking (blinding)
To avoid systematic differences between the treated and control groups during the course of the study in factors other than the one under study
Double-blindPatient, care provider, and investigator (person collecting data) all unaware of treatment assignment
Single-blindPatient unaware of treatment assignment
Blindness
Open label (unblinding)Single blinding (patients only)Double blinding (patients and investigators)Triple blinding (patients and investigators and Monitoring investigators)
Concerns in RCT
Loss to follow upLow compliancePublication bias
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