Number of Participants “At Risk” versus “Affected” in the Adverse Events Module
Results Reporting Modules
May 12, 2022- The number of participants affected is fairly self-explanatory: it is the number of participants in that arm or group who actually experienced that category or type of adverse event.
- The number of participants at risk is the total number of participants who were monitored for those adverse events in that arm or group. Usually this is the total number of participants in that arm or group. If the number differs from the group total, you should provide an explanation as to why in the Adverse Event Reporting Description field.
Like outcome measures, adverse events should be reported “per intervention”, so that anyone reading the data can tell which intervention participants were receiving at the time of the event.
For parallel design studies, this means that the total “at risk” will usually be the total number of participants in that arm.
Example: Parallel design study with 50 participants in “Drug A” arm and 50 participants in “Placebo” arm:
Serious Adverse Events
|
|
Drug A Affected/At Risk |
Placebo Affected/At Risk |
|
Total |
1/50 |
0/50 |
For crossover study designs however, this means that you will need to count some or all participants as “at risk” in both groups in order to report the total number of participants who were monitored for adverse events while they received each intervention:
Example: Crossover design study with 50 participants in “Drug A for 2 Weeks, then Drug B for 2 weeks” arm and 50 participants in “Drug B for 2 weeks, then Drug A for 2 weeks” arm:
Serious Adverse Events
|
|
Drug A Affected/At Risk |
Drug B Affected/At Risk |
|
Total |
1/100 |
0/100 |
The total number of participants in each group is 100 rather than 50 because all 100 received both Drug A and Drug B, even though they received the drugs in a different order depending on their study arm
For help entering your Adverse Events into ClinicalTrials.gov, visit the Adverse Events section of the PRS Guided Tutorials for Entering Results, or contact [email protected].