When undertaking any research, it is essential that you obtain data from people who are as representative as possible of the group you are studying. Even with the perfect questionnaire or interview guide (if such a thing exists), your data will only be regarded useful when your respondents are representative of the population as a whole. For this reason, a clear understanding of the principles of sampling is essential in order to conduct any type of research, whether quantitative or qualitative. Imagine a researcher investigating how tourism policies are developed for a destination or a country. This researcher obviously needs expert opinion, and most probably the views of those who develop policies. Even if the researcher develops an excellent question - naire or interview guide, appropriate responses will not be acquired if the people interviewed are local people and/or visiting tourists. These respondents will probably not have any idea about how policies are developed.