In a group interview, multiple participants engage in a group discussion, and talk about a specific theme. A perk of holding a group discussion is being able to collect new ideas and opinions that are formed through the group dynamics, which are unobtainable during depth interviews. The 6-7 participants influence each other and create a bandwagon effect.
A depth interview is a face-to-face interview, where the moderator asks the participant questions to get his/her opinion. The participant will be able to answer the questions more honestly and comfortably. This type of interview enables asking the participant more in depth about the psychology behind a purchase and consumer behavior (the process of selecting a product or service, the reason for purchasing etc.).
Group interviews are best for discovering and exploring ideas for new products, packaging and advertisement, and understanding the reactions, and reasons of consumers towards those ideas and prototypes.
Depth interviews are suitable for understanding the actions, opinions, attitudes and motives of the targeted consumers. For example, depth interviews are suitable for the purpose of creating persona, laddering and journey maps