Surveys need good planning and design in order to get a useful insight. For example, a
poorly designed survey (i.e. vague questions) can provide results with a high degree of
noise (i.e. inconsistent results). Nevertheless, other factors that are harder to control can
influence the results. For example, the subjects can be influenced by external aspects
(e.g. honesty and memory of the subjects) with respect to the questionnaire that can bias
the results (Passmore et al., 2002). Therefore, the planner of a survey needs to be aware
of issues that can influence on the results of the survey.