tl;dr know which participants you need to conduct research that generates value and design screeners to ensure that you get them.
We recently finished a round of interviews designed to put ourselves in a position to explain how experienced middle school teachers select literary texts to use in their ELA curricula.
We recruited people through social media, and screened those who responded to our call for participants. Our screeners were designed to produce a group of people with a certain level of domain expertise. We have a limited budget and we do everything we can to maximize the value we get out of each interview. If we only get one, then we need substantive answers to our important questions.
One interview with the right participant is far more valuable than five interviews with the wrong participants.
The wrong participants won’t have as much domain knowledge as they need to give good answers. They may not have enough experience to describe their processes let alone walk you through them. Worst case, they may not be engaged.
Engaged interviewees (and interviewers!) show it through their body language, tone of voice, and conversational responses. They may take an answer beyond where the interviewer imagined it could go due to their interest and excitement.
For the most part we had great participants because we had strong screeners. Participants sent us materials (unprompted) ahead of time, sent messages containing links to additional digital resources for us to review, screen-shared instructional materials to walk us through their selection processes, and more. They offered (and delivered) to answer follow up questions and schedule additional interviews to dive deeper into topics that came up during the first ones.
We achieved this outcome by design. We knew who we wanted to speak with; we wrote short character bios to capture the activities we wanted them to do, the domain knowledge we wanted them to have, the type of school where we wanted them to teach, and we wrote questions in order to identify them from among the pool of interested participants.
Know which participants you need to conduct research that generates value and design screeners to ensure that you get them.
Check out these useful resources for writing effective screeners:
Seven Steps to Writing a Screener Survey (on Medium so potentially behind a paywall)