To deepen the understanding of a market, custom research employs extensive or targeted primary research to go beyond what can be uncovered through secondary research only. In-depth interviews are the most versatile form of primary research, and are appropriate when targeting detailed perceptions, opinions, and attitudes. In-depth interviews are particularly effective when the goal is to capture feedback that is sensitive. These interviews can be conducted in-person or over the telephone to gain deeper insight to specific objectives by probing for quality responses. This offers an advantage over self-completion methods, such as surveys, because the respondent is more likely to give their full attention and the interviewer can deduce the quality of each response.