1.1. should be the one the investigators are most interested in answering
1.2. One that is capable of adequately answered
1.3. Reflects the primary objectives
1.4. Against which sample size is estimated
2. Secondary question
2.1. A variety of subsidiary or secondary questions related to the primary question
2.2. They could be of two types: - The response variable is different from that in the primary question - The response variable related to subgroup hypothesis
2.3. Must be: - Specified before data collection begins - Based on reasonable expectations - Limited in number
3. Ancillary Questions; sub-studies
3.1. Often clinical trials might be used to answer questions that do not bear directly on intervention being tested, but are nevertheless of interest
3.2. The structure of the trial and the ready access of participants may make it the ideal vehicle for such investigations
