Which statement about Multiple Primary Variables is true?

• A. It is never appropriate to have more than one primary variable.
• B. A single primary variable must be strictly primary.
• C. Each primary variable must be the same type of measurement.
• D. It may be desirable to use more than one primary variable, each sufficient to cover the range of effects.

Answer: (D)

In clinical research, it is acceptable and often desirable to have more than one primary variable when several clinically important effects need to be demonstrated. Each primary variable serves as a primary endpoint, and choosing multiple endpoints allows the study to cover a broader range of meaningful outcomes. This approach acknowledges that a treatment may improve more than one aspect of health, and each endpoint can provide evidence of benefit independently. It’s not required that all primary variables be the same type of measurement; different outcomes can be measured in different ways, as long as they are clearly defined and clinically relevant. Of course, when using multiple primary endpoints, the statistical plan must address multiplicity to control the risk of false positives.