Trial size and study population

A clinical trial must obviously have a control group against which the test (intervention) group can be compared. The control group may receive (a) no intervention at all (b) a placebo (i.e. a substance such as saline, which will have no pharmacological or other effect) (c) the therapy most commonly used at that time to combat the target disease/condition. 

The size of the trial will be limited by a number of factors, including  

While a comprehensive phase III trial would require at least several hundred patients, smaller trials would suffice if, for example  

Choosing the study population is obviously critical to adequate trial design. The specific criteria of patient eligibility should be clearly pre-defined as part of the primary question the trial strives 

Some clinical trial design types. Refer to text for 

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