Be sure that you haven t left anyone out ahead of time. Questions with an axe to grind not only affect the response, but may also repel some of the chosen sample from answering the survey. In a leading question, the phrasing used directs most people to a particular answer. A loaded question contains an implicit assumption or argument that influences choices. It is important to phrase all questions as neutrally as possible.
People are strange creatures.
We will unconsciously act to increase our status, bolster our self-image, make ourselves look good in the eyes of others, and say things that people like to hear. We are threatened by some subjects that we want to avoid and are ready to be contentious about others. Though most people would disagree with the generalizations, they are actually a source of considerable bias in survey results. There are steps you can take to limit this bias. Try abstracting issues, like talking about imaginary people instead of addressing the users themselves, as people might find their truthful answers embarrassing.