Even if a study reports all of its outcomes and provides all of the data for those outcomes, you might encounter other challenges:
1. None of the studies address an important outcome
2. Studies measure those outcomes using different scales or definitions
“Challenges with outcomes” isn’t a formal type of bias, but this category covers both of those instances and any other cases where your systematic review can’t compare important data across studies.
Either way, when this happens, your systematic review can’t capture the full picture of what happens when participants experience a particular treatment.
What should you do about these other challenges with outcomes?
There’s not much you as a researcher can do to counteract this problem, other than noting it as an issue in your report, but there is a growing movement to try to standardize outcomes across studies.
Here are some resources that you might want to check out:
Here’s a brief video about Core Outcome Sets.