No, but you need to account for it when considering efficacy, because people who choose to follow through on treatments may also be taking other steps that may also improve their outcomes, and it can be hard to tease out because the mere act of telling them they should have a screening might change other behaviours even without being prompted by doctors in a way that's recorded.
E.g. it's a reasonable hypothesis that patients who are more motivated to show up might also be more motivated to look up possible causes and what other steps they can take to improve their chances.
In other words, it's reasonable to expect people who comply to potentially get better at a higher rate than the efficacy of a single treatment, and teasing out how much of this effect is due to the intervention itself and how much is due to changed behaviour due to the referral is hard.
E.g. it's a reasonable hypothesis that patients who are more motivated to show up might also be more motivated to look up possible causes and what other steps they can take to improve their chances.
In other words, it's reasonable to expect people who comply to potentially get better at a higher rate than the efficacy of a single treatment, and teasing out how much of this effect is due to the intervention itself and how much is due to changed behaviour due to the referral is hard.