Over-invite in anticipation of a no-show rate of 10 to 20 percent.
But you will never want a group of more than 10 participants.
Offer an incentive. In 2006 dollars, a monetary incentive of $50 per
participant is probably the minimum you should consider. Other
incentive ideas include coupons, gift certificates, paid time off to
attend the group, or an opportunity to win a big-ticket item at a
drawing conducted at the focus group.