Within your survey design, you should use the option of including a survey comment box. Some people would only add one at the end of the survey, but you can include them after each section, or even after each question. Do, however, make it clear that your respondents are under no obligation to enter anything in the survey comment box.
The benefits are huge. Very often, people feel somewhat restricted by ranking and rating scales or multiple choice options. Sometimes they give an answer to a specific situation, when the question is actually more general.
They want to tell you about the motivation for their decisions, which is what they can do on the survey comment box. Allowing them to do so fills them with the confidence that your survey design is genuine and that you are interested in their replies.
But there are benefits for you as well. By including a survey comment box in your survey design you can decide whether or not there are certain answers that are invalid in terms of the data you collect. Besides this, it will teach you and show you how to improve any future surveys, should you wish to send them out again. Best of all, if you add a survey comment box asking people for their overall opinion or a service, product or experience, you will have gained some positive reinforcement. You can use this across your organisation to fill your staff with a sense of achievement.
It is very easy to include a comment box in your survey design and choosing not to have them is a real waste of great potential. The benefits, as you have seen, are felt not just by your respondents but also by you. Since those answering your online survey can simply click “next” if they don’t want to make any further comments, they also don’t get in anybody’s way, nor will they make people more reluctant to answer your questions.