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Why do we randomize?

Balances known and unknown pronostic (confounding) factors
Eliminate bias


5 sources of bias in RCTs

Inadequate random sequence generation
Inadequate concealment of random allocation
Inadequate blinding
Incomplete data for participants' outcomes
Violation of the intention-to-treat principle


What is adequate random sequence generation?

Can be a table of random numbers, a computer generated list of random numbers, a roll of a dice or flip of coin


What is adequate concealment of random allocation?

Can use a central randomization office, pre numbered or coded containers, or sequentially numbered, sealed, opaque envelopes


Crossover design
1. Assumptions
2. Advantages
3. Disadvantages

1. Chronic or recurrent condition, no carry over effect
2. Patients act as own control (less inter patient variation), can have a lower sample size
3. Cannot have carry over effect, need chronic disease state, cannot assess death and other major event outcomes


Factorial desgin

Evaluate 2 or more interventions compared with control in a single experiment
2 or more research questions/hypotheses


Randomized cluster/community design

Unit of randomization is a cluster
To avoid contamination
No need for consent in many areas


Issues with cluster design

Intra-class correlation coefficient p
Need larger sample size


Intention to treat analysis

Analyze patients in the group to which they were randomized (irrespective of adherence)


Per protocol analysis

Analyze only those who were adherent


As treated analysis

Analyze all those randomized according to what they actually received


Type 1 error

When you conclude something works when it does not


Type 2 error

When you conclude there is no difference between two treatments when there actually is