Following the previous post, it just occurred to me, by using some online techniques, could we also retain participants.

Not at all.

Thanks a lot.

That is a good idea! It has been found that using telephone interviews and sending (by mail, by e-mail, through intermediaries) the documents necessary to complete the interview in advance greatly facilitated participant retention. For example, it is difficult for many participants to get around (no transportation, insecure jobs with varied schedules, etc.) and also difficult to find places for in-person interviews that both are safe and guarantee confidentiality.