Once you’ve established the population you care about and the interventions you want to compare, your next step is deciding how you’ll measure the differences between your interventions. Are you interested in which intervention yields longer survival? Which cause the fewest hospitalizations? Which one is the safest? Which one results in the best quality of life? In other words, what are your definitions of success?
You do this by defining your outcomes.
Outcomes are the metrics you use to evaluate the treatment approaches in your question. They’re your yardstick for objectively saying which intervention is better.
Here’s another look at the your question:
You want to compare these two approaches to treating stage 5 chronic kidney disease, but what results are you using for this comparison?
Before you answer that question, take a moment to consider some of the types of outcomes you might use.