To question the sample respondents over time, marketers use a panel , a group of people who participate in a series of surveys. This also allows marketers to establish a dialogue with respondents. Limited contact reduces the possibility of bias. Bias may result when a researcher reveals emotional reactions, leading some respondents to modify their answers. Lengthy questionnaires are not appropriate.
Personal surveys provide in-depth answers, meeting respondents face to face.
In a focus group interview , a researcher meets with a group so 8 to 12 people to discuss a particular product or topic. Interviews may be videotaped or audiotaped. Focus groups are best used as exploratory research. Researchers can talk with respondents individually at their home or office or at a mall. Individual interviews conducted in shopping centers are known as mall intercepts.