Option D; QUALITATIVE METHODS
Explanation:
Qualitative market research is an open ended questions(conversational) based research methods that heavily depends on market research methods like; focus groups, in-depth interviews and other renovative research methods.
It is based on a small but highly validated sample size, the small size enables "cost saving" while the importance of the samples and the lack of a defined questionnaire allows free and in-depth discussion and analysis of topics.
Qualitative marketing researchers collect data ranging from focus group, case study, participation observation, innovation game and individual depth interview.
Therefore, the research methods Golf Digest Companies marketing research department used to help their client Callaway Golf Company are called QUALITATIVE METHODS.