In a clinical study of treatments for heart failure, researchers typically power their design to compare which outcome?

In a clinical study, researchers primarily focus on primary endpoints when powering their design because these endpoints represent the main outcomes that the study is intended to assess. The primary endpoint is the key measure of the effectiveness of a treatment; it is the main outcome that reflects the treatment’s impact on the health of the study participants.

By determining and powering the study based on the primary endpoint, researchers can ensure that the sample size is adequate to detect a statistically significant difference between treatment groups if one exists. This approach helps in maintaining the overall integrity and validity of the study results.

In contrast, secondary endpoints and subgroup analyses are often evaluated as supportive information rather than as primary measures of the treatment's efficacy. While adverse event rates are important for assessing safety, they do not typically serve as the main powered comparison outcome in the context of treating conditions like heart failure. They are monitored but are not the focus for powering a study. Thus, the emphasis on primary endpoints is crucial for the study's design and objectives, ensuring robust and reliable conclusions can be drawn regarding the effectiveness of the treatment being investigated.