I am not sure if the title describes my question here, but I am not sure whether I need to use the definite article in this context:
Qualitative research instruments include interviews, focus groups, reviews, and observation. [The] Interviews include either a series of structured questions, or allowing subjects to speak out their experience. [The] Focus groups allow gathering observations from a group of people who have similar properties. For instance, a group of men over 40. They give their opinions of the given topic. [The] review is done to collect scholarly written literature or other published materials to find attitudes towards a subject.
Do I need to use "the" in the bold sections in the paragraph above? If so, can you please explain the reason?