Research advice?

Hello parents of teens with diabetes,

I am the person doing research in psychology about self-esteem and chronic illness and have posted my study here and in several other places. Although the survey has been active since February, I have very few responses. I am writing again to seek your expert opinions on why you think teens do not seem to be participating. Reading through some of the other discussions, do you think it's the case that many are in denial and do not consider themselves a teen with diabetes? Is the survey (20-40 mins) too long? Do they not consider the incentive (1 of 10 $20 VISA gift cards and a grade prize of an ipod touch) worth it for them? Unfortunately the youths I spoke to did do the survey, so they didn't provide me with much insight. 

Basically - what would your kids say if you suggested this survey to them? Any advice would be great, thanks!