The in-person survey method usually requires hiring a large field staff to conduct the survey; this may include hiring multilingual interviewers. In addition to their salaries, firms must cover their traveling costs. Also, making sure that all the data is compiled correctly generally leads to hiring additional staff just to manage that responsibility. All of this adds up, making in-person surveys cost substantially more than other types of surveys.
When you take into account the travel time, as well as the unavoidable chitchat that occurs during in-person surveys, you realize that it will take weeks or even months to gather all the desired data. In-person surveys tend to take longer than any other survey mode. This can be problematic, especially when a long completion time contributes to expense.
Compared with other survey methods, in-person surveys offer respondents the least amount of anonymity. This may lead respondents to change their answers in order to avoid feeling uncomfortable in front of interviewers. For example, if interviewers ask a question about mental illness, then respondents may feel uneasy telling them that they take an antidepressant. This could lead respondents to deny that they have ever had any experience with mental illness.
With a written survey, every respondent sees the exact same wording for each question, and they receive no outside influence when choosing their answers. Things are a bit different with in-person surveys. For example, if in-person survey interviewers are very friendly, then they may receive answers that are skewed in a more-positive direction. However, if in-person survey interviewers are having a bad day and behave rudely, then they may get more-negative responses.