From our study, we have come to the conclusion that questionnaires have advantages over many types of surveys because they are cheap and can easily target groups of interest in many ways and they can be used to target a large audience in a wide geographical area. No matter which approach is chosen to collect data, it is impossible to get hundred percent response rates. All types of surveys have advantages and disadvantages; in some of them, the researchers have more control over the situation; for example the respondents can be influenced or get clues from interviewers to respond in certain ways.
Finally, we can conclude that questionnaires are the most commonly used in research because they can be applied in many different areas; for example, education, science, health care surveys and so on; whereas interviews can be too expensive, difficult to arrange and time consuming to be applied in a large geographical area.