iPerceptions uses a pre-post methodology where visitors are invited to participate in a survey as early as possible during their site visit. Visitors are then only asked to start the questionnaire after they have completed their visit.
This methodology provides a more balanced view of your website visitors, which may not occur if you invite only on exit. A negative bias may be seen in your feedback if this approach is taken because people who have had a negative experience may be more inclined to take a survey, as opposed to those whose experience went well.
Remember, invitations for iPerceptions Certified Surveys and Custom Surveys are shown when visitors enter a page that includes the iPerceptions script. This is why iPerceptions recommends placing the iPerceptions script on a global footer.