How might data be collected for this target response?Conduct one-on-one or group interviews to obtain detailed information and insights.
Identify several interventions that might help improve response rates. Place them in order with the least-restrictive at the top so that the interventions may be introduced systematically, adding more restrictive / less favorable interventions after the outcomes of less restrictive options have been measured.

Use multiple communication channels (email, social media, phone) to reach out to participants.