I am currently preparing my study on physical activity promotion in older Malaysians. My sample is not that small (about 200 people) and I am thinking of how to recruit them, and also retain them (9 months, 4 times data collection). I have read a few papers and also consulted some of the people from the community. I have a budget, but I can't spend all that much (want to avoid confounding as well). Please share your experience, or any information that you have.