Ratings are sensitive to mood. For example, a celebratory atmosphere in the room may improve ratings. In general, the more demographic items that are included, the more the fear of reprisal on the part of respondents. Trainees do not complete surveys. Participants don't want to complete long questionnaires from which they will not personally benefit.
Ratings are sensitive to wording nuances.
If you change a key word, the ratings change. Using loaded language or controversial terms can have serious and unknown effects on patterns of response. Free-form comments are almost always predominantly negative. They receive too much weight, though they often cannot be confirmed. It is better to ask for comments only in the pilot study that precedes a system-wide survey Here such remarks can be useful in making the final instrument more comprehensible and clear.